TOMOYO Linux Cross Reference
Linux/mm/filemap.c

   // SPDX-License-Identifier: GPL-2.0-only
   /*
    *      linux/mm/filemap.c
    *
    * Copyright (C) 1994-1999  Linus Torvalds
    */
   
   /*
    * This file handles the generic file mmap semantics used by
   * most "normal" filesystems (but you don't /have/ to use this:
   * the NFS filesystem used to do this differently, for example)
   */
  #include <linux/export.h>
  #include <linux/compiler.h>
  #include <linux/dax.h>
  #include <linux/fs.h>
  #include <linux/sched/signal.h>
  #include <linux/uaccess.h>
  #include <linux/capability.h>
  #include <linux/kernel_stat.h>
  #include <linux/gfp.h>
  #include <linux/mm.h>
  #include <linux/swap.h>
  #include <linux/swapops.h>
  #include <linux/syscalls.h>
  #include <linux/mman.h>
  #include <linux/pagemap.h>
  #include <linux/file.h>
  #include <linux/uio.h>
  #include <linux/error-injection.h>
  #include <linux/hash.h>
  #include <linux/writeback.h>
  #include <linux/backing-dev.h>
  #include <linux/pagevec.h>
  #include <linux/security.h>
  #include <linux/cpuset.h>
  #include <linux/hugetlb.h>
  #include <linux/memcontrol.h>
  #include <linux/shmem_fs.h>
  #include <linux/rmap.h>
  #include <linux/delayacct.h>
  #include <linux/psi.h>
  #include <linux/ramfs.h>
  #include <linux/page_idle.h>
  #include <linux/migrate.h>
  #include <linux/pipe_fs_i.h>
  #include <linux/splice.h>
  #include <linux/rcupdate_wait.h>
  #include <asm/pgalloc.h>
  #include <asm/tlbflush.h>
  #include "internal.h"
  
  #define CREATE_TRACE_POINTS
  #include <trace/events/filemap.h>
  
  /*
   * FIXME: remove all knowledge of the buffer layer from the core VM
   */
  #include <linux/buffer_head.h> /* for try_to_free_buffers */
  
  #include <asm/mman.h>
  
  #include "swap.h"
  
  /*
   * Shared mappings implemented 30.11.1994. It's not fully working yet,
   * though.
   *
   * Shared mappings now work. 15.8.1995  Bruno.
   *
   * finished 'unifying' the page and buffer cache and SMP-threaded the
   * page-cache, 21.05.1999, Ingo Molnar <mingo@redhat.com>
   *
   * SMP-threaded pagemap-LRU 1999, Andrea Arcangeli <andrea@suse.de>
   */
  
  /*
   * Lock ordering:
   *
   *  ->i_mmap_rwsem              (truncate_pagecache)
   *    ->private_lock            (__free_pte->block_dirty_folio)
   *      ->swap_lock             (exclusive_swap_page, others)
   *        ->i_pages lock
   *
   *  ->i_rwsem
   *    ->invalidate_lock         (acquired by fs in truncate path)
   *      ->i_mmap_rwsem          (truncate->unmap_mapping_range)
   *
   *  ->mmap_lock
   *    ->i_mmap_rwsem
   *      ->page_table_lock or pte_lock   (various, mainly in memory.c)
   *        ->i_pages lock        (arch-dependent flush_dcache_mmap_lock)
   *
   *  ->mmap_lock
   *    ->invalidate_lock         (filemap_fault)
   *      ->lock_page             (filemap_fault, access_process_vm)
   *
   *  ->i_rwsem                   (generic_perform_write)
   *    ->mmap_lock               (fault_in_readable->do_page_fault)
  *
  *  bdi->wb.list_lock
  *    sb_lock                   (fs/fs-writeback.c)
  *    ->i_pages lock            (__sync_single_inode)
  *
  *  ->i_mmap_rwsem
  *    ->anon_vma.lock           (vma_merge)
  *
  *  ->anon_vma.lock
  *    ->page_table_lock or pte_lock     (anon_vma_prepare and various)
  *
  *  ->page_table_lock or pte_lock
  *    ->swap_lock               (try_to_unmap_one)
  *    ->private_lock            (try_to_unmap_one)
  *    ->i_pages lock            (try_to_unmap_one)
  *    ->lruvec->lru_lock        (follow_page->mark_page_accessed)
  *    ->lruvec->lru_lock        (check_pte_range->isolate_lru_page)
  *    ->private_lock            (folio_remove_rmap_pte->set_page_dirty)
  *    ->i_pages lock            (folio_remove_rmap_pte->set_page_dirty)
  *    bdi.wb->list_lock         (folio_remove_rmap_pte->set_page_dirty)
  *    ->inode->i_lock           (folio_remove_rmap_pte->set_page_dirty)
  *    ->memcg->move_lock        (folio_remove_rmap_pte->folio_memcg_lock)
  *    bdi.wb->list_lock         (zap_pte_range->set_page_dirty)
  *    ->inode->i_lock           (zap_pte_range->set_page_dirty)
  *    ->private_lock            (zap_pte_range->block_dirty_folio)
  */
 
 static void mapping_set_update(struct xa_state *xas,
                 struct address_space *mapping)
 {
         if (dax_mapping(mapping) || shmem_mapping(mapping))
                 return;
         xas_set_update(xas, workingset_update_node);
         xas_set_lru(xas, &shadow_nodes);
 }
 
 static void page_cache_delete(struct address_space *mapping,
                                    struct folio *folio, void *shadow)
 {
         XA_STATE(xas, &mapping->i_pages, folio->index);
         long nr = 1;
 
         mapping_set_update(&xas, mapping);
 
         xas_set_order(&xas, folio->index, folio_order(folio));
         nr = folio_nr_pages(folio);
 
         VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
 
         xas_store(&xas, shadow);
         xas_init_marks(&xas);
 
         folio->mapping = NULL;
         /* Leave page->index set: truncation lookup relies upon it */
         mapping->nrpages -= nr;
 }
 
 static void filemap_unaccount_folio(struct address_space *mapping,
                 struct folio *folio)
 {
         long nr;
 
         VM_BUG_ON_FOLIO(folio_mapped(folio), folio);
         if (!IS_ENABLED(CONFIG_DEBUG_VM) && unlikely(folio_mapped(folio))) {
                 pr_alert("BUG: Bad page cache in process %s  pfn:%05lx\n",
                          current->comm, folio_pfn(folio));
                 dump_page(&folio->page, "still mapped when deleted");
                 dump_stack();
                 add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
 
                 if (mapping_exiting(mapping) && !folio_test_large(folio)) {
                         int mapcount = folio_mapcount(folio);
 
                         if (folio_ref_count(folio) >= mapcount + 2) {
                                 /*
                                  * All vmas have already been torn down, so it's
                                  * a good bet that actually the page is unmapped
                                  * and we'd rather not leak it: if we're wrong,
                                  * another bad page check should catch it later.
                                  */
                                 atomic_set(&folio->_mapcount, -1);
                                 folio_ref_sub(folio, mapcount);
                         }
                 }
         }
 
         /* hugetlb folios do not participate in page cache accounting. */
         if (folio_test_hugetlb(folio))
                 return;
 
         nr = folio_nr_pages(folio);
 
         __lruvec_stat_mod_folio(folio, NR_FILE_PAGES, -nr);
         if (folio_test_swapbacked(folio)) {
                 __lruvec_stat_mod_folio(folio, NR_SHMEM, -nr);
                 if (folio_test_pmd_mappable(folio))
                         __lruvec_stat_mod_folio(folio, NR_SHMEM_THPS, -nr);
         } else if (folio_test_pmd_mappable(folio)) {
                 __lruvec_stat_mod_folio(folio, NR_FILE_THPS, -nr);
                 filemap_nr_thps_dec(mapping);
         }
 
         /*
          * At this point folio must be either written or cleaned by
          * truncate.  Dirty folio here signals a bug and loss of
          * unwritten data - on ordinary filesystems.
          *
          * But it's harmless on in-memory filesystems like tmpfs; and can
          * occur when a driver which did get_user_pages() sets page dirty
          * before putting it, while the inode is being finally evicted.
          *
          * Below fixes dirty accounting after removing the folio entirely
          * but leaves the dirty flag set: it has no effect for truncated
          * folio and anyway will be cleared before returning folio to
          * buddy allocator.
          */
         if (WARN_ON_ONCE(folio_test_dirty(folio) &&
                          mapping_can_writeback(mapping)))
                 folio_account_cleaned(folio, inode_to_wb(mapping->host));
 }
 
 /*
  * Delete a page from the page cache and free it. Caller has to make
  * sure the page is locked and that nobody else uses it - or that usage
  * is safe.  The caller must hold the i_pages lock.
  */
 void __filemap_remove_folio(struct folio *folio, void *shadow)
 {
         struct address_space *mapping = folio->mapping;
 
         trace_mm_filemap_delete_from_page_cache(folio);
         filemap_unaccount_folio(mapping, folio);
         page_cache_delete(mapping, folio, shadow);
 }
 
 void filemap_free_folio(struct address_space *mapping, struct folio *folio)
 {
         void (*free_folio)(struct folio *);
         int refs = 1;
 
         free_folio = mapping->a_ops->free_folio;
         if (free_folio)
                 free_folio(folio);
 
         if (folio_test_large(folio))
                 refs = folio_nr_pages(folio);
         folio_put_refs(folio, refs);
 }
 
 /**
  * filemap_remove_folio - Remove folio from page cache.
  * @folio: The folio.
  *
  * This must be called only on folios that are locked and have been
  * verified to be in the page cache.  It will never put the folio into
  * the free list because the caller has a reference on the page.
  */
 void filemap_remove_folio(struct folio *folio)
 {
         struct address_space *mapping = folio->mapping;
 
         BUG_ON(!folio_test_locked(folio));
         spin_lock(&mapping->host->i_lock);
         xa_lock_irq(&mapping->i_pages);
         __filemap_remove_folio(folio, NULL);
         xa_unlock_irq(&mapping->i_pages);
         if (mapping_shrinkable(mapping))
                 inode_add_lru(mapping->host);
         spin_unlock(&mapping->host->i_lock);
 
         filemap_free_folio(mapping, folio);
 }
 
 /*
  * page_cache_delete_batch - delete several folios from page cache
  * @mapping: the mapping to which folios belong
  * @fbatch: batch of folios to delete
  *
  * The function walks over mapping->i_pages and removes folios passed in
  * @fbatch from the mapping. The function expects @fbatch to be sorted
  * by page index and is optimised for it to be dense.
  * It tolerates holes in @fbatch (mapping entries at those indices are not
  * modified).
  *
  * The function expects the i_pages lock to be held.
  */
 static void page_cache_delete_batch(struct address_space *mapping,
                              struct folio_batch *fbatch)
 {
         XA_STATE(xas, &mapping->i_pages, fbatch->folios[0]->index);
         long total_pages = 0;
         int i = 0;
         struct folio *folio;
 
         mapping_set_update(&xas, mapping);
         xas_for_each(&xas, folio, ULONG_MAX) {
                 if (i >= folio_batch_count(fbatch))
                         break;
 
                 /* A swap/dax/shadow entry got inserted? Skip it. */
                 if (xa_is_value(folio))
                         continue;
                 /*
                  * A page got inserted in our range? Skip it. We have our
                  * pages locked so they are protected from being removed.
                  * If we see a page whose index is higher than ours, it
                  * means our page has been removed, which shouldn't be
                  * possible because we're holding the PageLock.
                  */
                 if (folio != fbatch->folios[i]) {
                         VM_BUG_ON_FOLIO(folio->index >
                                         fbatch->folios[i]->index, folio);
                         continue;
                 }
 
                 WARN_ON_ONCE(!folio_test_locked(folio));
 
                 folio->mapping = NULL;
                 /* Leave folio->index set: truncation lookup relies on it */
 
                 i++;
                 xas_store(&xas, NULL);
                 total_pages += folio_nr_pages(folio);
         }
         mapping->nrpages -= total_pages;
 }
 
 void delete_from_page_cache_batch(struct address_space *mapping,
                                   struct folio_batch *fbatch)
 {
         int i;
 
         if (!folio_batch_count(fbatch))
                 return;
 
         spin_lock(&mapping->host->i_lock);
         xa_lock_irq(&mapping->i_pages);
         for (i = 0; i < folio_batch_count(fbatch); i++) {
                 struct folio *folio = fbatch->folios[i];
 
                 trace_mm_filemap_delete_from_page_cache(folio);
                 filemap_unaccount_folio(mapping, folio);
         }
         page_cache_delete_batch(mapping, fbatch);
         xa_unlock_irq(&mapping->i_pages);
         if (mapping_shrinkable(mapping))
                 inode_add_lru(mapping->host);
         spin_unlock(&mapping->host->i_lock);
 
         for (i = 0; i < folio_batch_count(fbatch); i++)
                 filemap_free_folio(mapping, fbatch->folios[i]);
 }
 
 int filemap_check_errors(struct address_space *mapping)
 {
         int ret = 0;
         /* Check for outstanding write errors */
         if (test_bit(AS_ENOSPC, &mapping->flags) &&
             test_and_clear_bit(AS_ENOSPC, &mapping->flags))
                 ret = -ENOSPC;
         if (test_bit(AS_EIO, &mapping->flags) &&
             test_and_clear_bit(AS_EIO, &mapping->flags))
                 ret = -EIO;
         return ret;
 }
 EXPORT_SYMBOL(filemap_check_errors);
 
 static int filemap_check_and_keep_errors(struct address_space *mapping)
 {
         /* Check for outstanding write errors */
         if (test_bit(AS_EIO, &mapping->flags))
                 return -EIO;
         if (test_bit(AS_ENOSPC, &mapping->flags))
                 return -ENOSPC;
         return 0;
 }
 
 /**
  * filemap_fdatawrite_wbc - start writeback on mapping dirty pages in range
  * @mapping:    address space structure to write
  * @wbc:        the writeback_control controlling the writeout
  *
  * Call writepages on the mapping using the provided wbc to control the
  * writeout.
  *
  * Return: %0 on success, negative error code otherwise.
  */
 int filemap_fdatawrite_wbc(struct address_space *mapping,
                            struct writeback_control *wbc)
 {
         int ret;
 
         if (!mapping_can_writeback(mapping) ||
             !mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
                 return 0;
 
         wbc_attach_fdatawrite_inode(wbc, mapping->host);
         ret = do_writepages(mapping, wbc);
         wbc_detach_inode(wbc);
         return ret;
 }
 EXPORT_SYMBOL(filemap_fdatawrite_wbc);
 
 /**
  * __filemap_fdatawrite_range - start writeback on mapping dirty pages in range
  * @mapping:    address space structure to write
  * @start:      offset in bytes where the range starts
  * @end:        offset in bytes where the range ends (inclusive)
  * @sync_mode:  enable synchronous operation
  *
  * Start writeback against all of a mapping's dirty pages that lie
  * within the byte offsets <start, end> inclusive.
  *
  * If sync_mode is WB_SYNC_ALL then this is a "data integrity" operation, as
  * opposed to a regular memory cleansing writeback.  The difference between
  * these two operations is that if a dirty page/buffer is encountered, it must
  * be waited upon, and not just skipped over.
  *
  * Return: %0 on success, negative error code otherwise.
  */
 int __filemap_fdatawrite_range(struct address_space *mapping, loff_t start,
                                 loff_t end, int sync_mode)
 {
         struct writeback_control wbc = {
                 .sync_mode = sync_mode,
                 .nr_to_write = LONG_MAX,
                 .range_start = start,
                 .range_end = end,
         };
 
         return filemap_fdatawrite_wbc(mapping, &wbc);
 }
 
 static inline int __filemap_fdatawrite(struct address_space *mapping,
         int sync_mode)
 {
         return __filemap_fdatawrite_range(mapping, 0, LLONG_MAX, sync_mode);
 }
 
 int filemap_fdatawrite(struct address_space *mapping)
 {
         return __filemap_fdatawrite(mapping, WB_SYNC_ALL);
 }
 EXPORT_SYMBOL(filemap_fdatawrite);
 
 int filemap_fdatawrite_range(struct address_space *mapping, loff_t start,
                                 loff_t end)
 {
         return __filemap_fdatawrite_range(mapping, start, end, WB_SYNC_ALL);
 }
 EXPORT_SYMBOL(filemap_fdatawrite_range);
 
 /**
  * filemap_flush - mostly a non-blocking flush
  * @mapping:    target address_space
  *
  * This is a mostly non-blocking flush.  Not suitable for data-integrity
  * purposes - I/O may not be started against all dirty pages.
  *
  * Return: %0 on success, negative error code otherwise.
  */
 int filemap_flush(struct address_space *mapping)
 {
         return __filemap_fdatawrite(mapping, WB_SYNC_NONE);
 }
 EXPORT_SYMBOL(filemap_flush);
 
 /**
  * filemap_range_has_page - check if a page exists in range.
  * @mapping:           address space within which to check
  * @start_byte:        offset in bytes where the range starts
  * @end_byte:          offset in bytes where the range ends (inclusive)
  *
  * Find at least one page in the range supplied, usually used to check if
  * direct writing in this range will trigger a writeback.
  *
  * Return: %true if at least one page exists in the specified range,
  * %false otherwise.
  */
 bool filemap_range_has_page(struct address_space *mapping,
                            loff_t start_byte, loff_t end_byte)
 {
         struct folio *folio;
         XA_STATE(xas, &mapping->i_pages, start_byte >> PAGE_SHIFT);
         pgoff_t max = end_byte >> PAGE_SHIFT;
 
         if (end_byte < start_byte)
                 return false;
 
         rcu_read_lock();
         for (;;) {
                 folio = xas_find(&xas, max);
                 if (xas_retry(&xas, folio))
                         continue;
                 /* Shadow entries don't count */
                 if (xa_is_value(folio))
                         continue;
                 /*
                  * We don't need to try to pin this page; we're about to
                  * release the RCU lock anyway.  It is enough to know that
                  * there was a page here recently.
                  */
                 break;
         }
         rcu_read_unlock();
 
         return folio != NULL;
 }
 EXPORT_SYMBOL(filemap_range_has_page);
 
 static void __filemap_fdatawait_range(struct address_space *mapping,
                                      loff_t start_byte, loff_t end_byte)
 {
         pgoff_t index = start_byte >> PAGE_SHIFT;
         pgoff_t end = end_byte >> PAGE_SHIFT;
         struct folio_batch fbatch;
         unsigned nr_folios;
 
         folio_batch_init(&fbatch);
 
         while (index <= end) {
                 unsigned i;
 
                 nr_folios = filemap_get_folios_tag(mapping, &index, end,
                                 PAGECACHE_TAG_WRITEBACK, &fbatch);
 
                 if (!nr_folios)
                         break;
 
                 for (i = 0; i < nr_folios; i++) {
                         struct folio *folio = fbatch.folios[i];
 
                         folio_wait_writeback(folio);
                         folio_clear_error(folio);
                 }
                 folio_batch_release(&fbatch);
                 cond_resched();
         }
 }
 
 /**
  * filemap_fdatawait_range - wait for writeback to complete
  * @mapping:            address space structure to wait for
  * @start_byte:         offset in bytes where the range starts
  * @end_byte:           offset in bytes where the range ends (inclusive)
  *
  * Walk the list of under-writeback pages of the given address space
  * in the given range and wait for all of them.  Check error status of
  * the address space and return it.
  *
  * Since the error status of the address space is cleared by this function,
  * callers are responsible for checking the return value and handling and/or
  * reporting the error.
  *
  * Return: error status of the address space.
  */
 int filemap_fdatawait_range(struct address_space *mapping, loff_t start_byte,
                             loff_t end_byte)
 {
         __filemap_fdatawait_range(mapping, start_byte, end_byte);
         return filemap_check_errors(mapping);
 }
 EXPORT_SYMBOL(filemap_fdatawait_range);
 
 /**
  * filemap_fdatawait_range_keep_errors - wait for writeback to complete
  * @mapping:            address space structure to wait for
  * @start_byte:         offset in bytes where the range starts
  * @end_byte:           offset in bytes where the range ends (inclusive)
  *
  * Walk the list of under-writeback pages of the given address space in the
  * given range and wait for all of them.  Unlike filemap_fdatawait_range(),
  * this function does not clear error status of the address space.
  *
  * Use this function if callers don't handle errors themselves.  Expected
  * call sites are system-wide / filesystem-wide data flushers: e.g. sync(2),
  * fsfreeze(8)
  */
 int filemap_fdatawait_range_keep_errors(struct address_space *mapping,
                 loff_t start_byte, loff_t end_byte)
 {
         __filemap_fdatawait_range(mapping, start_byte, end_byte);
         return filemap_check_and_keep_errors(mapping);
 }
 EXPORT_SYMBOL(filemap_fdatawait_range_keep_errors);
 
 /**
  * file_fdatawait_range - wait for writeback to complete
  * @file:               file pointing to address space structure to wait for
  * @start_byte:         offset in bytes where the range starts
  * @end_byte:           offset in bytes where the range ends (inclusive)
  *
  * Walk the list of under-writeback pages of the address space that file
  * refers to, in the given range and wait for all of them.  Check error
  * status of the address space vs. the file->f_wb_err cursor and return it.
  *
  * Since the error status of the file is advanced by this function,
  * callers are responsible for checking the return value and handling and/or
  * reporting the error.
  *
  * Return: error status of the address space vs. the file->f_wb_err cursor.
  */
 int file_fdatawait_range(struct file *file, loff_t start_byte, loff_t end_byte)
 {
         struct address_space *mapping = file->f_mapping;
 
         __filemap_fdatawait_range(mapping, start_byte, end_byte);
         return file_check_and_advance_wb_err(file);
 }
 EXPORT_SYMBOL(file_fdatawait_range);
 
 /**
  * filemap_fdatawait_keep_errors - wait for writeback without clearing errors
  * @mapping: address space structure to wait for
  *
  * Walk the list of under-writeback pages of the given address space
  * and wait for all of them.  Unlike filemap_fdatawait(), this function
  * does not clear error status of the address space.
  *
  * Use this function if callers don't handle errors themselves.  Expected
  * call sites are system-wide / filesystem-wide data flushers: e.g. sync(2),
  * fsfreeze(8)
  *
  * Return: error status of the address space.
  */
 int filemap_fdatawait_keep_errors(struct address_space *mapping)
 {
         __filemap_fdatawait_range(mapping, 0, LLONG_MAX);
         return filemap_check_and_keep_errors(mapping);
 }
 EXPORT_SYMBOL(filemap_fdatawait_keep_errors);
 
 /* Returns true if writeback might be needed or already in progress. */
 static bool mapping_needs_writeback(struct address_space *mapping)
 {
         return mapping->nrpages;
 }
 
 bool filemap_range_has_writeback(struct address_space *mapping,
                                  loff_t start_byte, loff_t end_byte)
 {
         XA_STATE(xas, &mapping->i_pages, start_byte >> PAGE_SHIFT);
         pgoff_t max = end_byte >> PAGE_SHIFT;
         struct folio *folio;
 
         if (end_byte < start_byte)
                 return false;
 
         rcu_read_lock();
         xas_for_each(&xas, folio, max) {
                 if (xas_retry(&xas, folio))
                         continue;
                 if (xa_is_value(folio))
                         continue;
                 if (folio_test_dirty(folio) || folio_test_locked(folio) ||
                                 folio_test_writeback(folio))
                         break;
         }
         rcu_read_unlock();
         return folio != NULL;
 }
 EXPORT_SYMBOL_GPL(filemap_range_has_writeback);
 
 /**
  * filemap_write_and_wait_range - write out & wait on a file range
  * @mapping:    the address_space for the pages
  * @lstart:     offset in bytes where the range starts
  * @lend:       offset in bytes where the range ends (inclusive)
  *
  * Write out and wait upon file offsets lstart->lend, inclusive.
  *
  * Note that @lend is inclusive (describes the last byte to be written) so
  * that this function can be used to write to the very end-of-file (end = -1).
  *
  * Return: error status of the address space.
  */
 int filemap_write_and_wait_range(struct address_space *mapping,
                                  loff_t lstart, loff_t lend)
 {
         int err = 0, err2;
 
         if (lend < lstart)
                 return 0;
 
         if (mapping_needs_writeback(mapping)) {
                 err = __filemap_fdatawrite_range(mapping, lstart, lend,
                                                  WB_SYNC_ALL);
                 /*
                  * Even if the above returned error, the pages may be
                  * written partially (e.g. -ENOSPC), so we wait for it.
                  * But the -EIO is special case, it may indicate the worst
                  * thing (e.g. bug) happened, so we avoid waiting for it.
                  */
                 if (err != -EIO)
                         __filemap_fdatawait_range(mapping, lstart, lend);
         }
         err2 = filemap_check_errors(mapping);
         if (!err)
                 err = err2;
         return err;
 }
 EXPORT_SYMBOL(filemap_write_and_wait_range);
 
 void __filemap_set_wb_err(struct address_space *mapping, int err)
 {
         errseq_t eseq = errseq_set(&mapping->wb_err, err);
 
         trace_filemap_set_wb_err(mapping, eseq);
 }
 EXPORT_SYMBOL(__filemap_set_wb_err);
 
 /**
  * file_check_and_advance_wb_err - report wb error (if any) that was previously
  *                                 and advance wb_err to current one
  * @file: struct file on which the error is being reported
  *
  * When userland calls fsync (or something like nfsd does the equivalent), we
  * want to report any writeback errors that occurred since the last fsync (or
  * since the file was opened if there haven't been any).
  *
  * Grab the wb_err from the mapping. If it matches what we have in the file,
  * then just quickly return 0. The file is all caught up.
  *
  * If it doesn't match, then take the mapping value, set the "seen" flag in
  * it and try to swap it into place. If it works, or another task beat us
  * to it with the new value, then update the f_wb_err and return the error
  * portion. The error at this point must be reported via proper channels
  * (a'la fsync, or NFS COMMIT operation, etc.).
  *
  * While we handle mapping->wb_err with atomic operations, the f_wb_err
  * value is protected by the f_lock since we must ensure that it reflects
  * the latest value swapped in for this file descriptor.
  *
  * Return: %0 on success, negative error code otherwise.
  */
 int file_check_and_advance_wb_err(struct file *file)
 {
         int err = 0;
         errseq_t old = READ_ONCE(file->f_wb_err);
         struct address_space *mapping = file->f_mapping;
 
         /* Locklessly handle the common case where nothing has changed */
         if (errseq_check(&mapping->wb_err, old)) {
                 /* Something changed, must use slow path */
                 spin_lock(&file->f_lock);
                 old = file->f_wb_err;
                 err = errseq_check_and_advance(&mapping->wb_err,
                                                 &file->f_wb_err);
                 trace_file_check_and_advance_wb_err(file, old);
                 spin_unlock(&file->f_lock);
         }
 
         /*
          * We're mostly using this function as a drop in replacement for
          * filemap_check_errors. Clear AS_EIO/AS_ENOSPC to emulate the effect
          * that the legacy code would have had on these flags.
          */
         clear_bit(AS_EIO, &mapping->flags);
         clear_bit(AS_ENOSPC, &mapping->flags);
         return err;
 }
 EXPORT_SYMBOL(file_check_and_advance_wb_err);
 
 /**
  * file_write_and_wait_range - write out & wait on a file range
  * @file:       file pointing to address_space with pages
  * @lstart:     offset in bytes where the range starts
  * @lend:       offset in bytes where the range ends (inclusive)
  *
  * Write out and wait upon file offsets lstart->lend, inclusive.
  *
  * Note that @lend is inclusive (describes the last byte to be written) so
  * that this function can be used to write to the very end-of-file (end = -1).
  *
  * After writing out and waiting on the data, we check and advance the
  * f_wb_err cursor to the latest value, and return any errors detected there.
  *
  * Return: %0 on success, negative error code otherwise.
  */
 int file_write_and_wait_range(struct file *file, loff_t lstart, loff_t lend)
 {
         int err = 0, err2;
         struct address_space *mapping = file->f_mapping;
 
         if (lend < lstart)
                 return 0;
 
         if (mapping_needs_writeback(mapping)) {
                 err = __filemap_fdatawrite_range(mapping, lstart, lend,
                                                  WB_SYNC_ALL);
                 /* See comment of filemap_write_and_wait() */
                 if (err != -EIO)
                         __filemap_fdatawait_range(mapping, lstart, lend);
         }
         err2 = file_check_and_advance_wb_err(file);
         if (!err)
                 err = err2;
         return err;
 }
 EXPORT_SYMBOL(file_write_and_wait_range);
 
 /**
  * replace_page_cache_folio - replace a pagecache folio with a new one
  * @old:        folio to be replaced
  * @new:        folio to replace with
  *
  * This function replaces a folio in the pagecache with a new one.  On
  * success it acquires the pagecache reference for the new folio and
  * drops it for the old folio.  Both the old and new folios must be
  * locked.  This function does not add the new folio to the LRU, the
  * caller must do that.
  *
  * The remove + add is atomic.  This function cannot fail.
  */
 void replace_page_cache_folio(struct folio *old, struct folio *new)
 {
         struct address_space *mapping = old->mapping;
         void (*free_folio)(struct folio *) = mapping->a_ops->free_folio;
         pgoff_t offset = old->index;
         XA_STATE(xas, &mapping->i_pages, offset);
 
         VM_BUG_ON_FOLIO(!folio_test_locked(old), old);
         VM_BUG_ON_FOLIO(!folio_test_locked(new), new);
         VM_BUG_ON_FOLIO(new->mapping, new);
 
         folio_get(new);
         new->mapping = mapping;
         new->index = offset;
 
         mem_cgroup_replace_folio(old, new);
 
         xas_lock_irq(&xas);
         xas_store(&xas, new);
 
         old->mapping = NULL;
         /* hugetlb pages do not participate in page cache accounting. */
         if (!folio_test_hugetlb(old))
                 __lruvec_stat_sub_folio(old, NR_FILE_PAGES);
         if (!folio_test_hugetlb(new))
                 __lruvec_stat_add_folio(new, NR_FILE_PAGES);
         if (folio_test_swapbacked(old))
                 __lruvec_stat_sub_folio(old, NR_SHMEM);
         if (folio_test_swapbacked(new))
                 __lruvec_stat_add_folio(new, NR_SHMEM);
         xas_unlock_irq(&xas);
         if (free_folio)
                 free_folio(old);
         folio_put(old);
 }
 EXPORT_SYMBOL_GPL(replace_page_cache_folio);
 
 noinline int __filemap_add_folio(struct address_space *mapping,
                 struct folio *folio, pgoff_t index, gfp_t gfp, void **shadowp)
 {
         XA_STATE(xas, &mapping->i_pages, index);
         void *alloced_shadow = NULL;
         int alloced_order = 0;
         bool huge;
         long nr;
 
         VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
         VM_BUG_ON_FOLIO(folio_test_swapbacked(folio), folio);
         mapping_set_update(&xas, mapping);
 
         VM_BUG_ON_FOLIO(index & (folio_nr_pages(folio) - 1), folio);
         xas_set_order(&xas, index, folio_order(folio));
         huge = folio_test_hugetlb(folio);
         nr = folio_nr_pages(folio);
 
         gfp &= GFP_RECLAIM_MASK;
         folio_ref_add(folio, nr);
         folio->mapping = mapping;
         folio->index = xas.xa_index;
 
         for (;;) {
                 int order = -1, split_order = 0;
                 void *entry, *old = NULL;
 
                 xas_lock_irq(&xas);
                 xas_for_each_conflict(&xas, entry) {
                         old = entry;
                         if (!xa_is_value(entry)) {
                                 xas_set_err(&xas, -EEXIST);
                                 goto unlock;
                         }
                         /*
                          * If a larger entry exists,
                          * it will be the first and only entry iterated.
                          */
                         if (order == -1)
                                 order = xas_get_order(&xas);
                 }
 
                 /* entry may have changed before we re-acquire the lock */
                 if (alloced_order && (old != alloced_shadow || order != alloced_order)) {
                         xas_destroy(&xas);
                         alloced_order = 0;
                 }
 
                 if (old) {
                         if (order > 0 && order > folio_order(folio)) {
                                 /* How to handle large swap entries? */
                                 BUG_ON(shmem_mapping(mapping));
                                 if (!alloced_order) {
                                         split_order = order;
                                         goto unlock;
                                 }
                                 xas_split(&xas, old, order);
                                 xas_reset(&xas);
                         }
                         if (shadowp)
                                 *shadowp = old;
                 }
 
                 xas_store(&xas, folio);
                 if (xas_error(&xas))
                         goto unlock;
 
                 mapping->nrpages += nr;
 
                 /* hugetlb pages do not participate in page cache accounting */
                 if (!huge) {
                         __lruvec_stat_mod_folio(folio, NR_FILE_PAGES, nr);
                         if (folio_test_pmd_mappable(folio))
                                 __lruvec_stat_mod_folio(folio,
                                                 NR_FILE_THPS, nr);
                 }
 
 unlock:
                 xas_unlock_irq(&xas);
 
                 /* split needed, alloc here and retry. */
                 if (split_order) {
                         xas_split_alloc(&xas, old, split_order, gfp);
                         if (xas_error(&xas))
                                 goto error;
                         alloced_shadow = old;
                         alloced_order = split_order;
                         xas_reset(&xas);
                         continue;
                 }
 
                 if (!xas_nomem(&xas, gfp))
                         break;
         }
 
         if (xas_error(&xas))
                 goto error;
 
         trace_mm_filemap_add_to_page_cache(folio);
         return 0;
 error:
         folio->mapping = NULL;
         /* Leave page->index set: truncation relies upon it */
         folio_put_refs(folio, nr);
         return xas_error(&xas);
 }
 ALLOW_ERROR_INJECTION(__filemap_add_folio, ERRNO);
 
 int filemap_add_folio(struct address_space *mapping, struct folio *folio,
                                 pgoff_t index, gfp_t gfp)
 {
         void *shadow = NULL;
         int ret;
 
         ret = mem_cgroup_charge(folio, NULL, gfp);
         if (ret)
                 return ret;
 
         __folio_set_locked(folio);
         ret = __filemap_add_folio(mapping, folio, index, gfp, &shadow);
         if (unlikely(ret)) {
                 mem_cgroup_uncharge(folio);
                 __folio_clear_locked(folio);
         } else {
                 /*
                  * The folio might have been evicted from cache only
                  * recently, in which case it should be activated like
                  * any other repeatedly accessed folio.
                  * The exception is folios getting rewritten; evicting other
                  * data from the working set, only to cache data that will
                  * get overwritten with something else, is a waste of memory.
                  */
                 WARN_ON_ONCE(folio_test_active(folio));
                 if (!(gfp & __GFP_WRITE) && shadow)
                         workingset_refault(folio, shadow);
                 folio_add_lru(folio);
         }
         return ret;
 }
 EXPORT_SYMBOL_GPL(filemap_add_folio);
 
 #ifdef CONFIG_NUMA
 struct folio *filemap_alloc_folio_noprof(gfp_t gfp, unsigned int order)
 {
         int n;
         struct folio *folio;
 
         if (cpuset_do_page_mem_spread()) {
                 unsigned int cpuset_mems_cookie;
                 do {
                         cpuset_mems_cookie = read_mems_allowed_begin();
                         n = cpuset_mem_spread_node();
                         folio = __folio_alloc_node_noprof(gfp, order, n);
                 } while (!folio && read_mems_allowed_retry(cpuset_mems_cookie));
 
                 return folio;
         }
         return folio_alloc_noprof(gfp, order);
 }
 EXPORT_SYMBOL(filemap_alloc_folio_noprof);
 #endif
 
 /*
  * filemap_invalidate_lock_two - lock invalidate_lock for two mappings
  *
  * Lock exclusively invalidate_lock of any passed mapping that is not NULL.
  *
  * @mapping1: the first mapping to lock
  * @mapping2: the second mapping to lock
  */
 void filemap_invalidate_lock_two(struct address_space *mapping1,
                                  struct address_space *mapping2)
 {
         if (mapping1 > mapping2)
                 swap(mapping1, mapping2);
         if (mapping1)
                 down_write(&mapping1->invalidate_lock);
         if (mapping2 && mapping1 != mapping2)
                 down_write_nested(&mapping2->invalidate_lock, 1);
 }
 EXPORT_SYMBOL(filemap_invalidate_lock_two);
 
 /*
  * filemap_invalidate_unlock_two - unlock invalidate_lock for two mappings
  *
  * Unlock exclusive invalidate_lock of any passed mapping that is not NULL.
  *
  * @mapping1: the first mapping to unlock
  * @mapping2: the second mapping to unlock
  */
 void filemap_invalidate_unlock_two(struct address_space *mapping1,
                                    struct address_space *mapping2)
 {
         if (mapping1)
                 up_write(&mapping1->invalidate_lock);
         if (mapping2 && mapping1 != mapping2)
                 up_write(&mapping2->invalidate_lock);
 }
 EXPORT_SYMBOL(filemap_invalidate_unlock_two);
 
 /*
  * In order to wait for pages to become available there must be
  * waitqueues associated with pages. By using a hash table of
  * waitqueues where the bucket discipline is to maintain all
  * waiters on the same queue and wake all when any of the pages
  * become available, and for the woken contexts to check to be
  * sure the appropriate page became available, this saves space
  * at a cost of "thundering herd" phenomena during rare hash
  * collisions.
  */
 #define PAGE_WAIT_TABLE_BITS 8
 #define PAGE_WAIT_TABLE_SIZE (1 << PAGE_WAIT_TABLE_BITS)
 static wait_queue_head_t folio_wait_table[PAGE_WAIT_TABLE_SIZE] __cacheline_aligned;
 
 static wait_queue_head_t *folio_waitqueue(struct folio *folio)
 {
         return &folio_wait_table[hash_ptr(folio, PAGE_WAIT_TABLE_BITS)];
 }
 
 void __init pagecache_init(void)
 {
         int i;
 
         for (i = 0; i < PAGE_WAIT_TABLE_SIZE; i++)
                 init_waitqueue_head(&folio_wait_table[i]);
 
         page_writeback_init();
 }
 
 /*
  * The page wait code treats the "wait->flags" somewhat unusually, because
  * we have multiple different kinds of waits, not just the usual "exclusive"
  * one.
  *
  * We have:
  *
  *  (a) no special bits set:
  *
  *      We're just waiting for the bit to be released, and when a waker
  *      calls the wakeup function, we set WQ_FLAG_WOKEN and wake it up,
  *      and remove it from the wait queue.
  *
  *      Simple and straightforward.
  *
  *  (b) WQ_FLAG_EXCLUSIVE:
  *
  *      The waiter is waiting to get the lock, and only one waiter should
  *      be woken up to avoid any thundering herd behavior. We'll set the
  *      WQ_FLAG_WOKEN bit, wake it up, and remove it from the wait queue.
  *
  *      This is the traditional exclusive wait.
  *
  *  (c) WQ_FLAG_EXCLUSIVE | WQ_FLAG_CUSTOM:
  *
  *      The waiter is waiting to get the bit, and additionally wants the
  *      lock to be transferred to it for fair lock behavior. If the lock
  *      cannot be taken, we stop walking the wait queue without waking
  *      the waiter.
  *
  *      This is the "fair lock handoff" case, and in addition to setting
  *      WQ_FLAG_WOKEN, we set WQ_FLAG_DONE to let the waiter easily see
  *      that it now has the lock.
  */
 static int wake_page_function(wait_queue_entry_t *wait, unsigned mode, int sync, void *arg)
 {
         unsigned int flags;
         struct wait_page_key *key = arg;
         struct wait_page_queue *wait_page
                 = container_of(wait, struct wait_page_queue, wait);
 
         if (!wake_page_match(wait_page, key))
                 return 0;
 
         /*
          * If it's a lock handoff wait, we get the bit for it, and
          * stop walking (and do not wake it up) if we can't.
          */
         flags = wait->flags;
         if (flags & WQ_FLAG_EXCLUSIVE) {
                 if (test_bit(key->bit_nr, &key->folio->flags))
                         return -1;
                 if (flags & WQ_FLAG_CUSTOM) {
                         if (test_and_set_bit(key->bit_nr, &key->folio->flags))
                                 return -1;
                         flags |= WQ_FLAG_DONE;
                 }
         }
 
         /*
          * We are holding the wait-queue lock, but the waiter that
          * is waiting for this will be checking the flags without
          * any locking.
          *
          * So update the flags atomically, and wake up the waiter
          * afterwards to avoid any races. This store-release pairs
          * with the load-acquire in folio_wait_bit_common().
          */
         smp_store_release(&wait->flags, flags | WQ_FLAG_WOKEN);
         wake_up_state(wait->private, mode);
 
         /*
          * Ok, we have successfully done what we're waiting for,
          * and we can unconditionally remove the wait entry.
          *
          * Note that this pairs with the "finish_wait()" in the
          * waiter, and has to be the absolute last thing we do.
          * After this list_del_init(&wait->entry) the wait entry
          * might be de-allocated and the process might even have
          * exited.
          */
         list_del_init_careful(&wait->entry);
         return (flags & WQ_FLAG_EXCLUSIVE) != 0;
 }
 
 static void folio_wake_bit(struct folio *folio, int bit_nr)
 {
         wait_queue_head_t *q = folio_waitqueue(folio);
         struct wait_page_key key;
         unsigned long flags;
 
         key.folio = folio;
         key.bit_nr = bit_nr;
         key.page_match = 0;
 
         spin_lock_irqsave(&q->lock, flags);
         __wake_up_locked_key(q, TASK_NORMAL, &key);
 
         /*
          * It's possible to miss clearing waiters here, when we woke our page
          * waiters, but the hashed waitqueue has waiters for other pages on it.
          * That's okay, it's a rare case. The next waker will clear it.
          *
          * Note that, depending on the page pool (buddy, hugetlb, ZONE_DEVICE,
          * other), the flag may be cleared in the course of freeing the page;
          * but that is not required for correctness.
          */
         if (!waitqueue_active(q) || !key.page_match)
                 folio_clear_waiters(folio);
 
         spin_unlock_irqrestore(&q->lock, flags);
 }
 
 /*
  * A choice of three behaviors for folio_wait_bit_common():
  */
 enum behavior {
         EXCLUSIVE,      /* Hold ref to page and take the bit when woken, like
                          * __folio_lock() waiting on then setting PG_locked.
                          */
         SHARED,         /* Hold ref to page and check the bit when woken, like
                          * folio_wait_writeback() waiting on PG_writeback.
                          */
         DROP,           /* Drop ref to page before wait, no check when woken,
                          * like folio_put_wait_locked() on PG_locked.
                          */
 };
 
 /*
  * Attempt to check (or get) the folio flag, and mark us done
  * if successful.
  */
 static inline bool folio_trylock_flag(struct folio *folio, int bit_nr,
                                         struct wait_queue_entry *wait)
 {
         if (wait->flags & WQ_FLAG_EXCLUSIVE) {
                 if (test_and_set_bit(bit_nr, &folio->flags))
                         return false;
         } else if (test_bit(bit_nr, &folio->flags))
                 return false;
 
         wait->flags |= WQ_FLAG_WOKEN | WQ_FLAG_DONE;
         return true;
 }
 
 /* How many times do we accept lock stealing from under a waiter? */
 int sysctl_page_lock_unfairness = 5;
 
 static inline int folio_wait_bit_common(struct folio *folio, int bit_nr,
                 int state, enum behavior behavior)
 {
         wait_queue_head_t *q = folio_waitqueue(folio);
         int unfairness = sysctl_page_lock_unfairness;
         struct wait_page_queue wait_page;
         wait_queue_entry_t *wait = &wait_page.wait;
         bool thrashing = false;
         unsigned long pflags;
         bool in_thrashing;
 
         if (bit_nr == PG_locked &&
             !folio_test_uptodate(folio) && folio_test_workingset(folio)) {
                 delayacct_thrashing_start(&in_thrashing);
                 psi_memstall_enter(&pflags);
                 thrashing = true;
         }
 
         init_wait(wait);
         wait->func = wake_page_function;
         wait_page.folio = folio;
         wait_page.bit_nr = bit_nr;
 
 repeat:
         wait->flags = 0;
         if (behavior == EXCLUSIVE) {
                 wait->flags = WQ_FLAG_EXCLUSIVE;
                 if (--unfairness < 0)
                         wait->flags |= WQ_FLAG_CUSTOM;
         }
 
         /*
          * Do one last check whether we can get the
          * page bit synchronously.
          *
          * Do the folio_set_waiters() marking before that
          * to let any waker we _just_ missed know they
          * need to wake us up (otherwise they'll never
          * even go to the slow case that looks at the
          * page queue), and add ourselves to the wait
          * queue if we need to sleep.
          *
          * This part needs to be done under the queue
          * lock to avoid races.
          */
         spin_lock_irq(&q->lock);
         folio_set_waiters(folio);
         if (!folio_trylock_flag(folio, bit_nr, wait))
                 __add_wait_queue_entry_tail(q, wait);
         spin_unlock_irq(&q->lock);
 
         /*
          * From now on, all the logic will be based on
          * the WQ_FLAG_WOKEN and WQ_FLAG_DONE flag, to
          * see whether the page bit testing has already
          * been done by the wake function.
          *
          * We can drop our reference to the folio.
          */
         if (behavior == DROP)
                 folio_put(folio);
 
         /*
          * Note that until the "finish_wait()", or until
          * we see the WQ_FLAG_WOKEN flag, we need to
          * be very careful with the 'wait->flags', because
          * we may race with a waker that sets them.
          */
         for (;;) {
                 unsigned int flags;
 
                 set_current_state(state);
 
                 /* Loop until we've been woken or interrupted */
                 flags = smp_load_acquire(&wait->flags);
                 if (!(flags & WQ_FLAG_WOKEN)) {
                         if (signal_pending_state(state, current))
                                 break;
 
                         io_schedule();
                         continue;
                 }
 
                 /* If we were non-exclusive, we're done */
                 if (behavior != EXCLUSIVE)
                         break;
 
                 /* If the waker got the lock for us, we're done */
                 if (flags & WQ_FLAG_DONE)
                         break;
 
                 /*
                  * Otherwise, if we're getting the lock, we need to
                  * try to get it ourselves.
                  *
                  * And if that fails, we'll have to retry this all.
                  */
                 if (unlikely(test_and_set_bit(bit_nr, folio_flags(folio, 0))))
                         goto repeat;
 
                 wait->flags |= WQ_FLAG_DONE;
                 break;
         }
 
         /*
          * If a signal happened, this 'finish_wait()' may remove the last
          * waiter from the wait-queues, but the folio waiters bit will remain
          * set. That's ok. The next wakeup will take care of it, and trying
          * to do it here would be difficult and prone to races.
          */
         finish_wait(q, wait);
 
         if (thrashing) {
                 delayacct_thrashing_end(&in_thrashing);
                 psi_memstall_leave(&pflags);
         }
 
         /*
          * NOTE! The wait->flags weren't stable until we've done the
          * 'finish_wait()', and we could have exited the loop above due
          * to a signal, and had a wakeup event happen after the signal
          * test but before the 'finish_wait()'.
          *
          * So only after the finish_wait() can we reliably determine
          * if we got woken up or not, so we can now figure out the final
          * return value based on that state without races.
          *
          * Also note that WQ_FLAG_WOKEN is sufficient for a non-exclusive
          * waiter, but an exclusive one requires WQ_FLAG_DONE.
          */
         if (behavior == EXCLUSIVE)
                 return wait->flags & WQ_FLAG_DONE ? 0 : -EINTR;
 
         return wait->flags & WQ_FLAG_WOKEN ? 0 : -EINTR;
 }
 
 #ifdef CONFIG_MIGRATION
 /**
  * migration_entry_wait_on_locked - Wait for a migration entry to be removed
  * @entry: migration swap entry.
  * @ptl: already locked ptl. This function will drop the lock.
  *
  * Wait for a migration entry referencing the given page to be removed. This is
  * equivalent to put_and_wait_on_page_locked(page, TASK_UNINTERRUPTIBLE) except
  * this can be called without taking a reference on the page. Instead this
  * should be called while holding the ptl for the migration entry referencing
  * the page.
  *
  * Returns after unlocking the ptl.
  *
  * This follows the same logic as folio_wait_bit_common() so see the comments
  * there.
  */
 void migration_entry_wait_on_locked(swp_entry_t entry, spinlock_t *ptl)
         __releases(ptl)
 {
         struct wait_page_queue wait_page;
         wait_queue_entry_t *wait = &wait_page.wait;
         bool thrashing = false;
         unsigned long pflags;
         bool in_thrashing;
         wait_queue_head_t *q;
         struct folio *folio = pfn_swap_entry_folio(entry);
 
         q = folio_waitqueue(folio);
         if (!folio_test_uptodate(folio) && folio_test_workingset(folio)) {
                 delayacct_thrashing_start(&in_thrashing);
                 psi_memstall_enter(&pflags);
                 thrashing = true;
         }
 
         init_wait(wait);
         wait->func = wake_page_function;
         wait_page.folio = folio;
         wait_page.bit_nr = PG_locked;
         wait->flags = 0;
 
         spin_lock_irq(&q->lock);
         folio_set_waiters(folio);
         if (!folio_trylock_flag(folio, PG_locked, wait))
                 __add_wait_queue_entry_tail(q, wait);
         spin_unlock_irq(&q->lock);
 
         /*
          * If a migration entry exists for the page the migration path must hold
          * a valid reference to the page, and it must take the ptl to remove the
          * migration entry. So the page is valid until the ptl is dropped.
          */
         spin_unlock(ptl);
 
         for (;;) {
                 unsigned int flags;
 
                 set_current_state(TASK_UNINTERRUPTIBLE);
 
                 /* Loop until we've been woken or interrupted */
                 flags = smp_load_acquire(&wait->flags);
                 if (!(flags & WQ_FLAG_WOKEN)) {
                         if (signal_pending_state(TASK_UNINTERRUPTIBLE, current))
                                 break;
 
                         io_schedule();
                         continue;
                 }
                 break;
         }
 
         finish_wait(q, wait);
 
         if (thrashing) {
                 delayacct_thrashing_end(&in_thrashing);
                 psi_memstall_leave(&pflags);
         }
 }
 #endif
 
 void folio_wait_bit(struct folio *folio, int bit_nr)
 {
         folio_wait_bit_common(folio, bit_nr, TASK_UNINTERRUPTIBLE, SHARED);
 }
 EXPORT_SYMBOL(folio_wait_bit);
 
 int folio_wait_bit_killable(struct folio *folio, int bit_nr)
 {
         return folio_wait_bit_common(folio, bit_nr, TASK_KILLABLE, SHARED);
 }
 EXPORT_SYMBOL(folio_wait_bit_killable);
 
 /**
  * folio_put_wait_locked - Drop a reference and wait for it to be unlocked
  * @folio: The folio to wait for.
  * @state: The sleep state (TASK_KILLABLE, TASK_UNINTERRUPTIBLE, etc).
  *
  * The caller should hold a reference on @folio.  They expect the page to
  * become unlocked relatively soon, but do not wish to hold up migration
  * (for example) by holding the reference while waiting for the folio to
  * come unlocked.  After this function returns, the caller should not
  * dereference @folio.
  *
  * Return: 0 if the folio was unlocked or -EINTR if interrupted by a signal.
  */
 static int folio_put_wait_locked(struct folio *folio, int state)
 {
         return folio_wait_bit_common(folio, PG_locked, state, DROP);
 }
 
 /**
  * folio_add_wait_queue - Add an arbitrary waiter to a folio's wait queue
  * @folio: Folio defining the wait queue of interest
  * @waiter: Waiter to add to the queue
  *
  * Add an arbitrary @waiter to the wait queue for the nominated @folio.
  */
 void folio_add_wait_queue(struct folio *folio, wait_queue_entry_t *waiter)
 {
         wait_queue_head_t *q = folio_waitqueue(folio);
         unsigned long flags;
 
         spin_lock_irqsave(&q->lock, flags);
         __add_wait_queue_entry_tail(q, waiter);
         folio_set_waiters(folio);
         spin_unlock_irqrestore(&q->lock, flags);
 }
 EXPORT_SYMBOL_GPL(folio_add_wait_queue);
 
 /**
  * folio_unlock - Unlock a locked folio.
  * @folio: The folio.
  *
  * Unlocks the folio and wakes up any thread sleeping on the page lock.
  *
  * Context: May be called from interrupt or process context.  May not be
  * called from NMI context.
  */
 void folio_unlock(struct folio *folio)
 {
         /* Bit 7 allows x86 to check the byte's sign bit */
         BUILD_BUG_ON(PG_waiters != 7);
         BUILD_BUG_ON(PG_locked > 7);
         VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
         if (folio_xor_flags_has_waiters(folio, 1 << PG_locked))
                 folio_wake_bit(folio, PG_locked);
 }
 EXPORT_SYMBOL(folio_unlock);
 
 /**
  * folio_end_read - End read on a folio.
  * @folio: The folio.
  * @success: True if all reads completed successfully.
  *
  * When all reads against a folio have completed, filesystems should
  * call this function to let the pagecache know that no more reads
  * are outstanding.  This will unlock the folio and wake up any thread
  * sleeping on the lock.  The folio will also be marked uptodate if all
  * reads succeeded.
  *
  * Context: May be called from interrupt or process context.  May not be
  * called from NMI context.
  */
 void folio_end_read(struct folio *folio, bool success)
 {
         unsigned long mask = 1 << PG_locked;
 
         /* Must be in bottom byte for x86 to work */
         BUILD_BUG_ON(PG_uptodate > 7);
         VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
         VM_BUG_ON_FOLIO(folio_test_uptodate(folio), folio);
 
         if (likely(success))
                 mask |= 1 << PG_uptodate;
         if (folio_xor_flags_has_waiters(folio, mask))
                 folio_wake_bit(folio, PG_locked);
 }
 EXPORT_SYMBOL(folio_end_read);
 
 /**
  * folio_end_private_2 - Clear PG_private_2 and wake any waiters.
  * @folio: The folio.
  *
  * Clear the PG_private_2 bit on a folio and wake up any sleepers waiting for
  * it.  The folio reference held for PG_private_2 being set is released.
  *
  * This is, for example, used when a netfs folio is being written to a local
  * disk cache, thereby allowing writes to the cache for the same folio to be
  * serialised.
  */
 void folio_end_private_2(struct folio *folio)
 {
         VM_BUG_ON_FOLIO(!folio_test_private_2(folio), folio);
         clear_bit_unlock(PG_private_2, folio_flags(folio, 0));
         folio_wake_bit(folio, PG_private_2);
         folio_put(folio);
 }
 EXPORT_SYMBOL(folio_end_private_2);
 
 /**
  * folio_wait_private_2 - Wait for PG_private_2 to be cleared on a folio.
  * @folio: The folio to wait on.
  *
  * Wait for PG_private_2 to be cleared on a folio.
  */
 void folio_wait_private_2(struct folio *folio)
 {
         while (folio_test_private_2(folio))
                 folio_wait_bit(folio, PG_private_2);
 }
 EXPORT_SYMBOL(folio_wait_private_2);
 
 /**
  * folio_wait_private_2_killable - Wait for PG_private_2 to be cleared on a folio.
  * @folio: The folio to wait on.
  *
  * Wait for PG_private_2 to be cleared on a folio or until a fatal signal is
  * received by the calling task.
  *
  * Return:
  * - 0 if successful.
  * - -EINTR if a fatal signal was encountered.
  */
 int folio_wait_private_2_killable(struct folio *folio)
 {
         int ret = 0;
 
         while (folio_test_private_2(folio)) {
                 ret = folio_wait_bit_killable(folio, PG_private_2);
                 if (ret < 0)
                         break;
         }
 
         return ret;
 }
 EXPORT_SYMBOL(folio_wait_private_2_killable);
 
 /**
  * folio_end_writeback - End writeback against a folio.
  * @folio: The folio.
  *
  * The folio must actually be under writeback.
  *
  * Context: May be called from process or interrupt context.
  */
 void folio_end_writeback(struct folio *folio)
 {
         VM_BUG_ON_FOLIO(!folio_test_writeback(folio), folio);
 
         /*
          * folio_test_clear_reclaim() could be used here but it is an
          * atomic operation and overkill in this particular case. Failing
          * to shuffle a folio marked for immediate reclaim is too mild
          * a gain to justify taking an atomic operation penalty at the
          * end of every folio writeback.
          */
         if (folio_test_reclaim(folio)) {
                 folio_clear_reclaim(folio);
                 folio_rotate_reclaimable(folio);
         }
 
         /*
          * Writeback does not hold a folio reference of its own, relying
          * on truncation to wait for the clearing of PG_writeback.
          * But here we must make sure that the folio is not freed and
          * reused before the folio_wake_bit().
          */
         folio_get(folio);
         if (__folio_end_writeback(folio))
                 folio_wake_bit(folio, PG_writeback);
         acct_reclaim_writeback(folio);
         folio_put(folio);
 }
 EXPORT_SYMBOL(folio_end_writeback);
 
 /**
  * __folio_lock - Get a lock on the folio, assuming we need to sleep to get it.
  * @folio: The folio to lock
  */
 void __folio_lock(struct folio *folio)
 {
         folio_wait_bit_common(folio, PG_locked, TASK_UNINTERRUPTIBLE,
                                 EXCLUSIVE);
 }
 EXPORT_SYMBOL(__folio_lock);
 
 int __folio_lock_killable(struct folio *folio)
 {
         return folio_wait_bit_common(folio, PG_locked, TASK_KILLABLE,
                                         EXCLUSIVE);
 }
 EXPORT_SYMBOL_GPL(__folio_lock_killable);
 
 static int __folio_lock_async(struct folio *folio, struct wait_page_queue *wait)
 {
         struct wait_queue_head *q = folio_waitqueue(folio);
         int ret;
 
         wait->folio = folio;
         wait->bit_nr = PG_locked;
 
         spin_lock_irq(&q->lock);
         __add_wait_queue_entry_tail(q, &wait->wait);
         folio_set_waiters(folio);
         ret = !folio_trylock(folio);
         /*
          * If we were successful now, we know we're still on the
          * waitqueue as we're still under the lock. This means it's
          * safe to remove and return success, we know the callback
          * isn't going to trigger.
          */
         if (!ret)
                 __remove_wait_queue(q, &wait->wait);
         else
                 ret = -EIOCBQUEUED;
         spin_unlock_irq(&q->lock);
         return ret;
 }
 
 /*
  * Return values:
  * 0 - folio is locked.
  * non-zero - folio is not locked.
  *     mmap_lock or per-VMA lock has been released (mmap_read_unlock() or
  *     vma_end_read()), unless flags had both FAULT_FLAG_ALLOW_RETRY and
  *     FAULT_FLAG_RETRY_NOWAIT set, in which case the lock is still held.
  *
  * If neither ALLOW_RETRY nor KILLABLE are set, will always return 0
  * with the folio locked and the mmap_lock/per-VMA lock is left unperturbed.
  */
 vm_fault_t __folio_lock_or_retry(struct folio *folio, struct vm_fault *vmf)
 {
         unsigned int flags = vmf->flags;
 
         if (fault_flag_allow_retry_first(flags)) {
                 /*
                  * CAUTION! In this case, mmap_lock/per-VMA lock is not
                  * released even though returning VM_FAULT_RETRY.
                  */
                 if (flags & FAULT_FLAG_RETRY_NOWAIT)
                         return VM_FAULT_RETRY;
 
                 release_fault_lock(vmf);
                 if (flags & FAULT_FLAG_KILLABLE)
                         folio_wait_locked_killable(folio);
                 else
                         folio_wait_locked(folio);
                 return VM_FAULT_RETRY;
         }
         if (flags & FAULT_FLAG_KILLABLE) {
                 bool ret;
 
                 ret = __folio_lock_killable(folio);
                 if (ret) {
                         release_fault_lock(vmf);
                         return VM_FAULT_RETRY;
                 }
         } else {
                 __folio_lock(folio);
         }
 
         return 0;
 }
 
 /**
  * page_cache_next_miss() - Find the next gap in the page cache.
  * @mapping: Mapping.
  * @index: Index.
  * @max_scan: Maximum range to search.
  *
  * Search the range [index, min(index + max_scan - 1, ULONG_MAX)] for the
  * gap with the lowest index.
  *
  * This function may be called under the rcu_read_lock.  However, this will
  * not atomically search a snapshot of the cache at a single point in time.
  * For example, if a gap is created at index 5, then subsequently a gap is
  * created at index 10, page_cache_next_miss covering both indices may
  * return 10 if called under the rcu_read_lock.
  *
  * Return: The index of the gap if found, otherwise an index outside the
  * range specified (in which case 'return - index >= max_scan' will be true).
  * In the rare case of index wrap-around, 0 will be returned.
  */
 pgoff_t page_cache_next_miss(struct address_space *mapping,
                              pgoff_t index, unsigned long max_scan)
 {
         XA_STATE(xas, &mapping->i_pages, index);
 
         while (max_scan--) {
                 void *entry = xas_next(&xas);
                 if (!entry || xa_is_value(entry))
                         return xas.xa_index;
                 if (xas.xa_index == 0)
                         return 0;
         }
 
         return index + max_scan;
 }
 EXPORT_SYMBOL(page_cache_next_miss);
 
 /**
  * page_cache_prev_miss() - Find the previous gap in the page cache.
  * @mapping: Mapping.
  * @index: Index.
  * @max_scan: Maximum range to search.
  *
  * Search the range [max(index - max_scan + 1, 0), index] for the
  * gap with the highest index.
  *
  * This function may be called under the rcu_read_lock.  However, this will
  * not atomically search a snapshot of the cache at a single point in time.
  * For example, if a gap is created at index 10, then subsequently a gap is
  * created at index 5, page_cache_prev_miss() covering both indices may
  * return 5 if called under the rcu_read_lock.
  *
  * Return: The index of the gap if found, otherwise an index outside the
  * range specified (in which case 'index - return >= max_scan' will be true).
  * In the rare case of wrap-around, ULONG_MAX will be returned.
  */
 pgoff_t page_cache_prev_miss(struct address_space *mapping,
                              pgoff_t index, unsigned long max_scan)
 {
         XA_STATE(xas, &mapping->i_pages, index);
 
         while (max_scan--) {
                 void *entry = xas_prev(&xas);
                 if (!entry || xa_is_value(entry))
                         break;
                 if (xas.xa_index == ULONG_MAX)
                         break;
         }
 
         return xas.xa_index;
 }
 EXPORT_SYMBOL(page_cache_prev_miss);
 
 /*
  * Lockless page cache protocol:
  * On the lookup side:
  * 1. Load the folio from i_pages
  * 2. Increment the refcount if it's not zero
  * 3. If the folio is not found by xas_reload(), put the refcount and retry
  *
  * On the removal side:
  * A. Freeze the page (by zeroing the refcount if nobody else has a reference)
  * B. Remove the page from i_pages
  * C. Return the page to the page allocator
  *
  * This means that any page may have its reference count temporarily
  * increased by a speculative page cache (or GUP-fast) lookup as it can
  * be allocated by another user before the RCU grace period expires.
  * Because the refcount temporarily acquired here may end up being the
  * last refcount on the page, any page allocation must be freeable by
  * folio_put().
  */
 
 /*
  * filemap_get_entry - Get a page cache entry.
  * @mapping: the address_space to search
  * @index: The page cache index.
  *
  * Looks up the page cache entry at @mapping & @index.  If it is a folio,
  * it is returned with an increased refcount.  If it is a shadow entry
  * of a previously evicted folio, or a swap entry from shmem/tmpfs,
  * it is returned without further action.
  *
  * Return: The folio, swap or shadow entry, %NULL if nothing is found.
  */
 void *filemap_get_entry(struct address_space *mapping, pgoff_t index)
 {
         XA_STATE(xas, &mapping->i_pages, index);
         struct folio *folio;
 
         rcu_read_lock();
 repeat:
         xas_reset(&xas);
         folio = xas_load(&xas);
         if (xas_retry(&xas, folio))
                 goto repeat;
         /*
          * A shadow entry of a recently evicted page, or a swap entry from
          * shmem/tmpfs.  Return it without attempting to raise page count.
          */
         if (!folio || xa_is_value(folio))
                 goto out;
 
         if (!folio_try_get(folio))
                 goto repeat;
 
         if (unlikely(folio != xas_reload(&xas))) {
                 folio_put(folio);
                 goto repeat;
         }
 out:
         rcu_read_unlock();
 
         return folio;
 }
 
 /**
  * __filemap_get_folio - Find and get a reference to a folio.
  * @mapping: The address_space to search.
  * @index: The page index.
  * @fgp_flags: %FGP flags modify how the folio is returned.
  * @gfp: Memory allocation flags to use if %FGP_CREAT is specified.
  *
  * Looks up the page cache entry at @mapping & @index.
  *
  * If %FGP_LOCK or %FGP_CREAT are specified then the function may sleep even
  * if the %GFP flags specified for %FGP_CREAT are atomic.
  *
  * If this function returns a folio, it is returned with an increased refcount.
  *
  * Return: The found folio or an ERR_PTR() otherwise.
  */
 struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
                 fgf_t fgp_flags, gfp_t gfp)
 {
         struct folio *folio;
 
 repeat:
         folio = filemap_get_entry(mapping, index);
         if (xa_is_value(folio))
                 folio = NULL;
         if (!folio)
                 goto no_page;
 
         if (fgp_flags & FGP_LOCK) {
                 if (fgp_flags & FGP_NOWAIT) {
                         if (!folio_trylock(folio)) {
                                 folio_put(folio);
                                 return ERR_PTR(-EAGAIN);
                         }
                 } else {
                         folio_lock(folio);
                 }
 
                 /* Has the page been truncated? */
                 if (unlikely(folio->mapping != mapping)) {
                         folio_unlock(folio);
                         folio_put(folio);
                         goto repeat;
                 }
                 VM_BUG_ON_FOLIO(!folio_contains(folio, index), folio);
         }
 
         if (fgp_flags & FGP_ACCESSED)
                 folio_mark_accessed(folio);
         else if (fgp_flags & FGP_WRITE) {
                 /* Clear idle flag for buffer write */
                 if (folio_test_idle(folio))
                         folio_clear_idle(folio);
         }
 
         if (fgp_flags & FGP_STABLE)
                 folio_wait_stable(folio);
 no_page:
         if (!folio && (fgp_flags & FGP_CREAT)) {
                 unsigned order = FGF_GET_ORDER(fgp_flags);
                 int err;
 
                 if ((fgp_flags & FGP_WRITE) && mapping_can_writeback(mapping))
                         gfp |= __GFP_WRITE;
                 if (fgp_flags & FGP_NOFS)
                         gfp &= ~__GFP_FS;
                 if (fgp_flags & FGP_NOWAIT) {
                         gfp &= ~GFP_KERNEL;
                         gfp |= GFP_NOWAIT | __GFP_NOWARN;
                 }
                 if (WARN_ON_ONCE(!(fgp_flags & (FGP_LOCK | FGP_FOR_MMAP))))
                         fgp_flags |= FGP_LOCK;
 
                 if (!mapping_large_folio_support(mapping))
                         order = 0;
                 if (order > MAX_PAGECACHE_ORDER)
                         order = MAX_PAGECACHE_ORDER;
                 /* If we're not aligned, allocate a smaller folio */
                 if (index & ((1UL << order) - 1))
                         order = __ffs(index);
 
                 do {
                         gfp_t alloc_gfp = gfp;
 
                         err = -ENOMEM;
                         if (order > 0)
                                 alloc_gfp |= __GFP_NORETRY | __GFP_NOWARN;
                         folio = filemap_alloc_folio(alloc_gfp, order);
                         if (!folio)
                                 continue;
 
                         /* Init accessed so avoid atomic mark_page_accessed later */
                         if (fgp_flags & FGP_ACCESSED)
                                 __folio_set_referenced(folio);
 
                         err = filemap_add_folio(mapping, folio, index, gfp);
                         if (!err)
                                 break;
                         folio_put(folio);
                         folio = NULL;
                 } while (order-- > 0);
 
                 if (err == -EEXIST)
                         goto repeat;
                 if (err)
                         return ERR_PTR(err);
                 /*
                  * filemap_add_folio locks the page, and for mmap
                  * we expect an unlocked page.
                  */
                 if (folio && (fgp_flags & FGP_FOR_MMAP))
                         folio_unlock(folio);
         }
 
         if (!folio)
                 return ERR_PTR(-ENOENT);
         return folio;
 }
 EXPORT_SYMBOL(__filemap_get_folio);
 
 static inline struct folio *find_get_entry(struct xa_state *xas, pgoff_t max,
                 xa_mark_t mark)
 {
         struct folio *folio;
 
 retry:
         if (mark == XA_PRESENT)
                 folio = xas_find(xas, max);
         else
                 folio = xas_find_marked(xas, max, mark);
 
         if (xas_retry(xas, folio))
                 goto retry;
         /*
          * A shadow entry of a recently evicted page, a swap
          * entry from shmem/tmpfs or a DAX entry.  Return it
          * without attempting to raise page count.
          */
         if (!folio || xa_is_value(folio))
                 return folio;
 
         if (!folio_try_get(folio))
                 goto reset;
 
         if (unlikely(folio != xas_reload(xas))) {
                 folio_put(folio);
                 goto reset;
         }
 
         return folio;
 reset:
         xas_reset(xas);
         goto retry;
 }
 
 /**
  * find_get_entries - gang pagecache lookup
  * @mapping:    The address_space to search
  * @start:      The starting page cache index
  * @end:        The final page index (inclusive).
  * @fbatch:     Where the resulting entries are placed.
  * @indices:    The cache indices corresponding to the entries in @entries
  *
  * find_get_entries() will search for and return a batch of entries in
  * the mapping.  The entries are placed in @fbatch.  find_get_entries()
  * takes a reference on any actual folios it returns.
  *
  * The entries have ascending indexes.  The indices may not be consecutive
  * due to not-present entries or large folios.
  *
  * Any shadow entries of evicted folios, or swap entries from
  * shmem/tmpfs, are included in the returned array.
  *
  * Return: The number of entries which were found.
  */
 unsigned find_get_entries(struct address_space *mapping, pgoff_t *start,
                 pgoff_t end, struct folio_batch *fbatch, pgoff_t *indices)
 {
         XA_STATE(xas, &mapping->i_pages, *start);
         struct folio *folio;
 
         rcu_read_lock();
         while ((folio = find_get_entry(&xas, end, XA_PRESENT)) != NULL) {
                 indices[fbatch->nr] = xas.xa_index;
                 if (!folio_batch_add(fbatch, folio))
                         break;
         }
         rcu_read_unlock();
 
         if (folio_batch_count(fbatch)) {
                 unsigned long nr = 1;
                 int idx = folio_batch_count(fbatch) - 1;
 
                 folio = fbatch->folios[idx];
                 if (!xa_is_value(folio))
                         nr = folio_nr_pages(folio);
                 *start = indices[idx] + nr;
         }
         return folio_batch_count(fbatch);
 }
 
 /**
  * find_lock_entries - Find a batch of pagecache entries.
  * @mapping:    The address_space to search.
  * @start:      The starting page cache index.
  * @end:        The final page index (inclusive).
  * @fbatch:     Where the resulting entries are placed.
  * @indices:    The cache indices of the entries in @fbatch.
  *
  * find_lock_entries() will return a batch of entries from @mapping.
  * Swap, shadow and DAX entries are included.  Folios are returned
  * locked and with an incremented refcount.  Folios which are locked
  * by somebody else or under writeback are skipped.  Folios which are
  * partially outside the range are not returned.
  *
  * The entries have ascending indexes.  The indices may not be consecutive
  * due to not-present entries, large folios, folios which could not be
  * locked or folios under writeback.
  *
  * Return: The number of entries which were found.
  */
 unsigned find_lock_entries(struct address_space *mapping, pgoff_t *start,
                 pgoff_t end, struct folio_batch *fbatch, pgoff_t *indices)
 {
         XA_STATE(xas, &mapping->i_pages, *start);
         struct folio *folio;
 
         rcu_read_lock();
         while ((folio = find_get_entry(&xas, end, XA_PRESENT))) {
                 if (!xa_is_value(folio)) {
                         if (folio->index < *start)
                                 goto put;
                         if (folio_next_index(folio) - 1 > end)
                                 goto put;
                         if (!folio_trylock(folio))
                                 goto put;
                         if (folio->mapping != mapping ||
                             folio_test_writeback(folio))
                                 goto unlock;
                         VM_BUG_ON_FOLIO(!folio_contains(folio, xas.xa_index),
                                         folio);
                 }
                 indices[fbatch->nr] = xas.xa_index;
                 if (!folio_batch_add(fbatch, folio))
                         break;
                 continue;
 unlock:
                 folio_unlock(folio);
 put:
                 folio_put(folio);
         }
         rcu_read_unlock();
 
         if (folio_batch_count(fbatch)) {
                 unsigned long nr = 1;
                 int idx = folio_batch_count(fbatch) - 1;
 
                 folio = fbatch->folios[idx];
                 if (!xa_is_value(folio))
                         nr = folio_nr_pages(folio);
                 *start = indices[idx] + nr;
         }
         return folio_batch_count(fbatch);
 }
 
 /**
  * filemap_get_folios - Get a batch of folios
  * @mapping:    The address_space to search
  * @start:      The starting page index
  * @end:        The final page index (inclusive)
  * @fbatch:     The batch to fill.
  *
  * Search for and return a batch of folios in the mapping starting at
  * index @start and up to index @end (inclusive).  The folios are returned
  * in @fbatch with an elevated reference count.
  *
  * Return: The number of folios which were found.
  * We also update @start to index the next folio for the traversal.
  */
 unsigned filemap_get_folios(struct address_space *mapping, pgoff_t *start,
                 pgoff_t end, struct folio_batch *fbatch)
 {
         return filemap_get_folios_tag(mapping, start, end, XA_PRESENT, fbatch);
 }
 EXPORT_SYMBOL(filemap_get_folios);
 
 /**
  * filemap_get_folios_contig - Get a batch of contiguous folios
  * @mapping:    The address_space to search
  * @start:      The starting page index
  * @end:        The final page index (inclusive)
  * @fbatch:     The batch to fill
  *
  * filemap_get_folios_contig() works exactly like filemap_get_folios(),
  * except the returned folios are guaranteed to be contiguous. This may
  * not return all contiguous folios if the batch gets filled up.
  *
  * Return: The number of folios found.
  * Also update @start to be positioned for traversal of the next folio.
  */
 
 unsigned filemap_get_folios_contig(struct address_space *mapping,
                 pgoff_t *start, pgoff_t end, struct folio_batch *fbatch)
 {
         XA_STATE(xas, &mapping->i_pages, *start);
         unsigned long nr;
         struct folio *folio;
 
         rcu_read_lock();
 
         for (folio = xas_load(&xas); folio && xas.xa_index <= end;
                         folio = xas_next(&xas)) {
                 if (xas_retry(&xas, folio))
                         continue;
                 /*
                  * If the entry has been swapped out, we can stop looking.
                  * No current caller is looking for DAX entries.
                  */
                 if (xa_is_value(folio))
                         goto update_start;
 
                 /* If we landed in the middle of a THP, continue at its end. */
                 if (xa_is_sibling(folio))
                         goto update_start;
 
                 if (!folio_try_get(folio))
                         goto retry;
 
                 if (unlikely(folio != xas_reload(&xas)))
                         goto put_folio;
 
                 if (!folio_batch_add(fbatch, folio)) {
                         nr = folio_nr_pages(folio);
                         *start = folio->index + nr;
                         goto out;
                 }
                 continue;
 put_folio:
                 folio_put(folio);
 
 retry:
                 xas_reset(&xas);
         }
 
 update_start:
         nr = folio_batch_count(fbatch);
 
         if (nr) {
                 folio = fbatch->folios[nr - 1];
                 *start = folio_next_index(folio);
         }
 out:
         rcu_read_unlock();
         return folio_batch_count(fbatch);
 }
 EXPORT_SYMBOL(filemap_get_folios_contig);
 
 /**
  * filemap_get_folios_tag - Get a batch of folios matching @tag
  * @mapping:    The address_space to search
  * @start:      The starting page index
  * @end:        The final page index (inclusive)
  * @tag:        The tag index
  * @fbatch:     The batch to fill
  *
  * The first folio may start before @start; if it does, it will contain
  * @start.  The final folio may extend beyond @end; if it does, it will
  * contain @end.  The folios have ascending indices.  There may be gaps
  * between the folios if there are indices which have no folio in the
  * page cache.  If folios are added to or removed from the page cache
  * while this is running, they may or may not be found by this call.
  * Only returns folios that are tagged with @tag.
  *
  * Return: The number of folios found.
  * Also update @start to index the next folio for traversal.
  */
 unsigned filemap_get_folios_tag(struct address_space *mapping, pgoff_t *start,
                         pgoff_t end, xa_mark_t tag, struct folio_batch *fbatch)
 {
         XA_STATE(xas, &mapping->i_pages, *start);
         struct folio *folio;
 
         rcu_read_lock();
         while ((folio = find_get_entry(&xas, end, tag)) != NULL) {
                 /*
                  * Shadow entries should never be tagged, but this iteration
                  * is lockless so there is a window for page reclaim to evict
                  * a page we saw tagged. Skip over it.
                  */
                 if (xa_is_value(folio))
                         continue;
                 if (!folio_batch_add(fbatch, folio)) {
                         unsigned long nr = folio_nr_pages(folio);
                         *start = folio->index + nr;
                         goto out;
                 }
         }
         /*
          * We come here when there is no page beyond @end. We take care to not
          * overflow the index @start as it confuses some of the callers. This
          * breaks the iteration when there is a page at index -1 but that is
          * already broke anyway.
          */
         if (end == (pgoff_t)-1)
                 *start = (pgoff_t)-1;
         else
                 *start = end + 1;
 out:
         rcu_read_unlock();
 
         return folio_batch_count(fbatch);
 }
 EXPORT_SYMBOL(filemap_get_folios_tag);
 
 /*
  * CD/DVDs are error prone. When a medium error occurs, the driver may fail
  * a _large_ part of the i/o request. Imagine the worst scenario:
  *
  *      ---R__________________________________________B__________
  *         ^ reading here                             ^ bad block(assume 4k)
  *
  * read(R) => miss => readahead(R...B) => media error => frustrating retries
  * => failing the whole request => read(R) => read(R+1) =>
  * readahead(R+1...B+1) => bang => read(R+2) => read(R+3) =>
  * readahead(R+3...B+2) => bang => read(R+3) => read(R+4) =>
  * readahead(R+4...B+3) => bang => read(R+4) => read(R+5) => ......
  *
  * It is going insane. Fix it by quickly scaling down the readahead size.
  */
 static void shrink_readahead_size_eio(struct file_ra_state *ra)
 {
         ra->ra_pages /= 4;
 }
 
 /*
  * filemap_get_read_batch - Get a batch of folios for read
  *
  * Get a batch of folios which represent a contiguous range of bytes in
  * the file.  No exceptional entries will be returned.  If @index is in
  * the middle of a folio, the entire folio will be returned.  The last
  * folio in the batch may have the readahead flag set or the uptodate flag
  * clear so that the caller can take the appropriate action.
  */
 static void filemap_get_read_batch(struct address_space *mapping,
                 pgoff_t index, pgoff_t max, struct folio_batch *fbatch)
 {
         XA_STATE(xas, &mapping->i_pages, index);
         struct folio *folio;
 
         rcu_read_lock();
         for (folio = xas_load(&xas); folio; folio = xas_next(&xas)) {
                 if (xas_retry(&xas, folio))
                         continue;
                 if (xas.xa_index > max || xa_is_value(folio))
                         break;
                 if (xa_is_sibling(folio))
                         break;
                 if (!folio_try_get(folio))
                         goto retry;
 
                 if (unlikely(folio != xas_reload(&xas)))
                         goto put_folio;
 
                 if (!folio_batch_add(fbatch, folio))
                         break;
                 if (!folio_test_uptodate(folio))
                         break;
                 if (folio_test_readahead(folio))
                         break;
                 xas_advance(&xas, folio_next_index(folio) - 1);
                 continue;
 put_folio:
                 folio_put(folio);
 retry:
                 xas_reset(&xas);
         }
         rcu_read_unlock();
 }
 
 static int filemap_read_folio(struct file *file, filler_t filler,
                 struct folio *folio)
 {
         bool workingset = folio_test_workingset(folio);
         unsigned long pflags;
         int error;
 
         /*
          * A previous I/O error may have been due to temporary failures,
          * eg. multipath errors.  PG_error will be set again if read_folio
          * fails.
          */
         folio_clear_error(folio);
 
         /* Start the actual read. The read will unlock the page. */
         if (unlikely(workingset))
                 psi_memstall_enter(&pflags);
         error = filler(file, folio);
         if (unlikely(workingset))
                 psi_memstall_leave(&pflags);
         if (error)
                 return error;
 
         error = folio_wait_locked_killable(folio);
         if (error)
                 return error;
         if (folio_test_uptodate(folio))
                 return 0;
         if (file)
                 shrink_readahead_size_eio(&file->f_ra);
         return -EIO;
 }
 
 static bool filemap_range_uptodate(struct address_space *mapping,
                 loff_t pos, size_t count, struct folio *folio,
                 bool need_uptodate)
 {
         if (folio_test_uptodate(folio))
                 return true;
         /* pipes can't handle partially uptodate pages */
         if (need_uptodate)
                 return false;
         if (!mapping->a_ops->is_partially_uptodate)
                 return false;
         if (mapping->host->i_blkbits >= folio_shift(folio))
                 return false;
 
         if (folio_pos(folio) > pos) {
                 count -= folio_pos(folio) - pos;
                 pos = 0;
         } else {
                 pos -= folio_pos(folio);
         }
 
         return mapping->a_ops->is_partially_uptodate(folio, pos, count);
 }
 
 static int filemap_update_page(struct kiocb *iocb,
                 struct address_space *mapping, size_t count,
                 struct folio *folio, bool need_uptodate)
 {
         int error;
 
         if (iocb->ki_flags & IOCB_NOWAIT) {
                 if (!filemap_invalidate_trylock_shared(mapping))
                         return -EAGAIN;
         } else {
                 filemap_invalidate_lock_shared(mapping);
         }
 
         if (!folio_trylock(folio)) {
                 error = -EAGAIN;
                 if (iocb->ki_flags & (IOCB_NOWAIT | IOCB_NOIO))
                         goto unlock_mapping;
                 if (!(iocb->ki_flags & IOCB_WAITQ)) {
                         filemap_invalidate_unlock_shared(mapping);
                         /*
                          * This is where we usually end up waiting for a
                          * previously submitted readahead to finish.
                          */
                         folio_put_wait_locked(folio, TASK_KILLABLE);
                         return AOP_TRUNCATED_PAGE;
                 }
                 error = __folio_lock_async(folio, iocb->ki_waitq);
                 if (error)
                         goto unlock_mapping;
         }
 
         error = AOP_TRUNCATED_PAGE;
         if (!folio->mapping)
                 goto unlock;
 
         error = 0;
         if (filemap_range_uptodate(mapping, iocb->ki_pos, count, folio,
                                    need_uptodate))
                 goto unlock;
 
         error = -EAGAIN;
         if (iocb->ki_flags & (IOCB_NOIO | IOCB_NOWAIT | IOCB_WAITQ))
                 goto unlock;
 
         error = filemap_read_folio(iocb->ki_filp, mapping->a_ops->read_folio,
                         folio);
         goto unlock_mapping;
 unlock:
         folio_unlock(folio);
 unlock_mapping:
         filemap_invalidate_unlock_shared(mapping);
         if (error == AOP_TRUNCATED_PAGE)
                 folio_put(folio);
         return error;
 }
 
 static int filemap_create_folio(struct file *file,
                 struct address_space *mapping, pgoff_t index,
                 struct folio_batch *fbatch)
 {
         struct folio *folio;
         int error;
 
         folio = filemap_alloc_folio(mapping_gfp_mask(mapping), 0);
         if (!folio)
                 return -ENOMEM;
 
         /*
          * Protect against truncate / hole punch. Grabbing invalidate_lock
          * here assures we cannot instantiate and bring uptodate new
          * pagecache folios after evicting page cache during truncate
          * and before actually freeing blocks.  Note that we could
          * release invalidate_lock after inserting the folio into
          * the page cache as the locked folio would then be enough to
          * synchronize with hole punching. But there are code paths
          * such as filemap_update_page() filling in partially uptodate
          * pages or ->readahead() that need to hold invalidate_lock
          * while mapping blocks for IO so let's hold the lock here as
          * well to keep locking rules simple.
          */
         filemap_invalidate_lock_shared(mapping);
         error = filemap_add_folio(mapping, folio, index,
                         mapping_gfp_constraint(mapping, GFP_KERNEL));
         if (error == -EEXIST)
                 error = AOP_TRUNCATED_PAGE;
         if (error)
                 goto error;
 
         error = filemap_read_folio(file, mapping->a_ops->read_folio, folio);
         if (error)
                 goto error;
 
         filemap_invalidate_unlock_shared(mapping);
         folio_batch_add(fbatch, folio);
         return 0;
 error:
         filemap_invalidate_unlock_shared(mapping);
         folio_put(folio);
         return error;
 }
 
 static int filemap_readahead(struct kiocb *iocb, struct file *file,
                 struct address_space *mapping, struct folio *folio,
                 pgoff_t last_index)
 {
         DEFINE_READAHEAD(ractl, file, &file->f_ra, mapping, folio->index);
 
         if (iocb->ki_flags & IOCB_NOIO)
                 return -EAGAIN;
         page_cache_async_ra(&ractl, folio, last_index - folio->index);
         return 0;
 }
 
 static int filemap_get_pages(struct kiocb *iocb, size_t count,
                 struct folio_batch *fbatch, bool need_uptodate)
 {
         struct file *filp = iocb->ki_filp;
         struct address_space *mapping = filp->f_mapping;
         struct file_ra_state *ra = &filp->f_ra;
         pgoff_t index = iocb->ki_pos >> PAGE_SHIFT;
         pgoff_t last_index;
         struct folio *folio;
         int err = 0;
 
         /* "last_index" is the index of the page beyond the end of the read */
         last_index = DIV_ROUND_UP(iocb->ki_pos + count, PAGE_SIZE);
 retry:
         if (fatal_signal_pending(current))
                 return -EINTR;
 
         filemap_get_read_batch(mapping, index, last_index - 1, fbatch);
         if (!folio_batch_count(fbatch)) {
                 if (iocb->ki_flags & IOCB_NOIO)
                         return -EAGAIN;
                 page_cache_sync_readahead(mapping, ra, filp, index,
                                 last_index - index);
                 filemap_get_read_batch(mapping, index, last_index - 1, fbatch);
         }
         if (!folio_batch_count(fbatch)) {
                 if (iocb->ki_flags & (IOCB_NOWAIT | IOCB_WAITQ))
                         return -EAGAIN;
                 err = filemap_create_folio(filp, mapping,
                                 iocb->ki_pos >> PAGE_SHIFT, fbatch);
                 if (err == AOP_TRUNCATED_PAGE)
                         goto retry;
                 return err;
         }
 
         folio = fbatch->folios[folio_batch_count(fbatch) - 1];
         if (folio_test_readahead(folio)) {
                 err = filemap_readahead(iocb, filp, mapping, folio, last_index);
                 if (err)
                         goto err;
         }
         if (!folio_test_uptodate(folio)) {
                 if ((iocb->ki_flags & IOCB_WAITQ) &&
                     folio_batch_count(fbatch) > 1)
                         iocb->ki_flags |= IOCB_NOWAIT;
                 err = filemap_update_page(iocb, mapping, count, folio,
                                           need_uptodate);
                 if (err)
                         goto err;
         }
 
         return 0;
 err:
         if (err < 0)
                 folio_put(folio);
         if (likely(--fbatch->nr))
                 return 0;
         if (err == AOP_TRUNCATED_PAGE)
                 goto retry;
         return err;
 }
 
 static inline bool pos_same_folio(loff_t pos1, loff_t pos2, struct folio *folio)
 {
         unsigned int shift = folio_shift(folio);
 
         return (pos1 >> shift == pos2 >> shift);
 }
 
 /**
  * filemap_read - Read data from the page cache.
  * @iocb: The iocb to read.
  * @iter: Destination for the data.
  * @already_read: Number of bytes already read by the caller.
  *
  * Copies data from the page cache.  If the data is not currently present,
  * uses the readahead and read_folio address_space operations to fetch it.
  *
  * Return: Total number of bytes copied, including those already read by
  * the caller.  If an error happens before any bytes are copied, returns
  * a negative error number.
  */
 ssize_t filemap_read(struct kiocb *iocb, struct iov_iter *iter,
                 ssize_t already_read)
 {
         struct file *filp = iocb->ki_filp;
         struct file_ra_state *ra = &filp->f_ra;
         struct address_space *mapping = filp->f_mapping;
         struct inode *inode = mapping->host;
         struct folio_batch fbatch;
         int i, error = 0;
         bool writably_mapped;
         loff_t isize, end_offset;
         loff_t last_pos = ra->prev_pos;
 
         if (unlikely(iocb->ki_pos >= inode->i_sb->s_maxbytes))
                 return 0;
         if (unlikely(!iov_iter_count(iter)))
                 return 0;
 
         iov_iter_truncate(iter, inode->i_sb->s_maxbytes);
         folio_batch_init(&fbatch);
 
         do {
                 cond_resched();
 
                 /*
                  * If we've already successfully copied some data, then we
                  * can no longer safely return -EIOCBQUEUED. Hence mark
                  * an async read NOWAIT at that point.
                  */
                 if ((iocb->ki_flags & IOCB_WAITQ) && already_read)
                         iocb->ki_flags |= IOCB_NOWAIT;
 
                 if (unlikely(iocb->ki_pos >= i_size_read(inode)))
                         break;
 
                 error = filemap_get_pages(iocb, iter->count, &fbatch, false);
                 if (error < 0)
                         break;
 
                 /*
                  * i_size must be checked after we know the pages are Uptodate.
                  *
                  * Checking i_size after the check allows us to calculate
                  * the correct value for "nr", which means the zero-filled
                  * part of the page is not copied back to userspace (unless
                  * another truncate extends the file - this is desired though).
                  */
                 isize = i_size_read(inode);
                 if (unlikely(iocb->ki_pos >= isize))
                         goto put_folios;
                 end_offset = min_t(loff_t, isize, iocb->ki_pos + iter->count);
 
                 /*
                  * Once we start copying data, we don't want to be touching any
                  * cachelines that might be contended:
                  */
                 writably_mapped = mapping_writably_mapped(mapping);
 
                 /*
                  * When a read accesses the same folio several times, only
                  * mark it as accessed the first time.
                  */
                 if (!pos_same_folio(iocb->ki_pos, last_pos - 1,
                                     fbatch.folios[0]))
                         folio_mark_accessed(fbatch.folios[0]);
 
                 for (i = 0; i < folio_batch_count(&fbatch); i++) {
                         struct folio *folio = fbatch.folios[i];
                         size_t fsize = folio_size(folio);
                         size_t offset = iocb->ki_pos & (fsize - 1);
                         size_t bytes = min_t(loff_t, end_offset - iocb->ki_pos,
                                              fsize - offset);
                         size_t copied;
 
                         if (end_offset < folio_pos(folio))
                                 break;
                         if (i > 0)
                                 folio_mark_accessed(folio);
                         /*
                          * If users can be writing to this folio using arbitrary
                          * virtual addresses, take care of potential aliasing
                          * before reading the folio on the kernel side.
                          */
                         if (writably_mapped)
                                 flush_dcache_folio(folio);
 
                         copied = copy_folio_to_iter(folio, offset, bytes, iter);
 
                         already_read += copied;
                         iocb->ki_pos += copied;
                         last_pos = iocb->ki_pos;
 
                         if (copied < bytes) {
                                 error = -EFAULT;
                                 break;
                         }
                 }
 put_folios:
                 for (i = 0; i < folio_batch_count(&fbatch); i++)
                         folio_put(fbatch.folios[i]);
                 folio_batch_init(&fbatch);
         } while (iov_iter_count(iter) && iocb->ki_pos < isize && !error);
 
         file_accessed(filp);
         ra->prev_pos = last_pos;
         return already_read ? already_read : error;
 }
 EXPORT_SYMBOL_GPL(filemap_read);
 
 int kiocb_write_and_wait(struct kiocb *iocb, size_t count)
 {
         struct address_space *mapping = iocb->ki_filp->f_mapping;
         loff_t pos = iocb->ki_pos;
         loff_t end = pos + count - 1;
 
         if (iocb->ki_flags & IOCB_NOWAIT) {
                 if (filemap_range_needs_writeback(mapping, pos, end))
                         return -EAGAIN;
                 return 0;
         }
 
         return filemap_write_and_wait_range(mapping, pos, end);
 }
 EXPORT_SYMBOL_GPL(kiocb_write_and_wait);
 
 int kiocb_invalidate_pages(struct kiocb *iocb, size_t count)
 {
         struct address_space *mapping = iocb->ki_filp->f_mapping;
         loff_t pos = iocb->ki_pos;
         loff_t end = pos + count - 1;
         int ret;
 
         if (iocb->ki_flags & IOCB_NOWAIT) {
                 /* we could block if there are any pages in the range */
                 if (filemap_range_has_page(mapping, pos, end))
                         return -EAGAIN;
         } else {
                 ret = filemap_write_and_wait_range(mapping, pos, end);
                 if (ret)
                         return ret;
         }
 
         /*
          * After a write we want buffered reads to be sure to go to disk to get
          * the new data.  We invalidate clean cached page from the region we're
          * about to write.  We do this *before* the write so that we can return
          * without clobbering -EIOCBQUEUED from ->direct_IO().
          */
         return invalidate_inode_pages2_range(mapping, pos >> PAGE_SHIFT,
                                              end >> PAGE_SHIFT);
 }
 EXPORT_SYMBOL_GPL(kiocb_invalidate_pages);
 
 /**
  * generic_file_read_iter - generic filesystem read routine
  * @iocb:       kernel I/O control block
  * @iter:       destination for the data read
  *
  * This is the "read_iter()" routine for all filesystems
  * that can use the page cache directly.
  *
  * The IOCB_NOWAIT flag in iocb->ki_flags indicates that -EAGAIN shall
  * be returned when no data can be read without waiting for I/O requests
  * to complete; it doesn't prevent readahead.
  *
  * The IOCB_NOIO flag in iocb->ki_flags indicates that no new I/O
  * requests shall be made for the read or for readahead.  When no data
  * can be read, -EAGAIN shall be returned.  When readahead would be
  * triggered, a partial, possibly empty read shall be returned.
  *
  * Return:
  * * number of bytes copied, even for partial reads
  * * negative error code (or 0 if IOCB_NOIO) if nothing was read
  */
 ssize_t
 generic_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
 {
         size_t count = iov_iter_count(iter);
         ssize_t retval = 0;
 
         if (!count)
                 return 0; /* skip atime */
 
         if (iocb->ki_flags & IOCB_DIRECT) {
                 struct file *file = iocb->ki_filp;
                 struct address_space *mapping = file->f_mapping;
                 struct inode *inode = mapping->host;
 
                 retval = kiocb_write_and_wait(iocb, count);
                 if (retval < 0)
                         return retval;
                 file_accessed(file);
 
                 retval = mapping->a_ops->direct_IO(iocb, iter);
                 if (retval >= 0) {
                         iocb->ki_pos += retval;
                         count -= retval;
                 }
                 if (retval != -EIOCBQUEUED)
                         iov_iter_revert(iter, count - iov_iter_count(iter));
 
                 /*
                  * Btrfs can have a short DIO read if we encounter
                  * compressed extents, so if there was an error, or if
                  * we've already read everything we wanted to, or if
                  * there was a short read because we hit EOF, go ahead
                  * and return.  Otherwise fallthrough to buffered io for
                  * the rest of the read.  Buffered reads will not work for
                  * DAX files, so don't bother trying.
                  */
                 if (retval < 0 || !count || IS_DAX(inode))
                         return retval;
                 if (iocb->ki_pos >= i_size_read(inode))
                         return retval;
         }
 
         return filemap_read(iocb, iter, retval);
 }
 EXPORT_SYMBOL(generic_file_read_iter);
 
 /*
  * Splice subpages from a folio into a pipe.
  */
 size_t splice_folio_into_pipe(struct pipe_inode_info *pipe,
                               struct folio *folio, loff_t fpos, size_t size)
 {
         struct page *page;
         size_t spliced = 0, offset = offset_in_folio(folio, fpos);
 
         page = folio_page(folio, offset / PAGE_SIZE);
         size = min(size, folio_size(folio) - offset);
         offset %= PAGE_SIZE;
 
         while (spliced < size &&
                !pipe_full(pipe->head, pipe->tail, pipe->max_usage)) {
                 struct pipe_buffer *buf = pipe_head_buf(pipe);
                 size_t part = min_t(size_t, PAGE_SIZE - offset, size - spliced);
 
                 *buf = (struct pipe_buffer) {
                         .ops    = &page_cache_pipe_buf_ops,
                         .page   = page,
                         .offset = offset,
                         .len    = part,
                 };
                 folio_get(folio);
                 pipe->head++;
                 page++;
                 spliced += part;
                 offset = 0;
         }
 
         return spliced;
 }
 
 /**
  * filemap_splice_read -  Splice data from a file's pagecache into a pipe
  * @in: The file to read from
  * @ppos: Pointer to the file position to read from
  * @pipe: The pipe to splice into
  * @len: The amount to splice
  * @flags: The SPLICE_F_* flags
  *
  * This function gets folios from a file's pagecache and splices them into the
  * pipe.  Readahead will be called as necessary to fill more folios.  This may
  * be used for blockdevs also.
  *
  * Return: On success, the number of bytes read will be returned and *@ppos
  * will be updated if appropriate; 0 will be returned if there is no more data
  * to be read; -EAGAIN will be returned if the pipe had no space, and some
  * other negative error code will be returned on error.  A short read may occur
  * if the pipe has insufficient space, we reach the end of the data or we hit a
  * hole.
  */
 ssize_t filemap_splice_read(struct file *in, loff_t *ppos,
                             struct pipe_inode_info *pipe,
                             size_t len, unsigned int flags)
 {
         struct folio_batch fbatch;
         struct kiocb iocb;
         size_t total_spliced = 0, used, npages;
         loff_t isize, end_offset;
         bool writably_mapped;
         int i, error = 0;
 
         if (unlikely(*ppos >= in->f_mapping->host->i_sb->s_maxbytes))
                 return 0;
 
         init_sync_kiocb(&iocb, in);
         iocb.ki_pos = *ppos;
 
         /* Work out how much data we can actually add into the pipe */
         used = pipe_occupancy(pipe->head, pipe->tail);
         npages = max_t(ssize_t, pipe->max_usage - used, 0);
         len = min_t(size_t, len, npages * PAGE_SIZE);
 
         folio_batch_init(&fbatch);
 
         do {
                 cond_resched();
 
                 if (*ppos >= i_size_read(in->f_mapping->host))
                         break;
 
                 iocb.ki_pos = *ppos;
                 error = filemap_get_pages(&iocb, len, &fbatch, true);
                 if (error < 0)
                         break;
 
                 /*
                  * i_size must be checked after we know the pages are Uptodate.
                  *
                  * Checking i_size after the check allows us to calculate
                  * the correct value for "nr", which means the zero-filled
                  * part of the page is not copied back to userspace (unless
                  * another truncate extends the file - this is desired though).
                  */
                 isize = i_size_read(in->f_mapping->host);
                 if (unlikely(*ppos >= isize))
                         break;
                 end_offset = min_t(loff_t, isize, *ppos + len);
 
                 /*
                  * Once we start copying data, we don't want to be touching any
                  * cachelines that might be contended:
                  */
                 writably_mapped = mapping_writably_mapped(in->f_mapping);
 
                 for (i = 0; i < folio_batch_count(&fbatch); i++) {
                         struct folio *folio = fbatch.folios[i];
                         size_t n;
 
                         if (folio_pos(folio) >= end_offset)
                                 goto out;
                         folio_mark_accessed(folio);
 
                         /*
                          * If users can be writing to this folio using arbitrary
                          * virtual addresses, take care of potential aliasing
                          * before reading the folio on the kernel side.
                          */
                         if (writably_mapped)
                                 flush_dcache_folio(folio);
 
                         n = min_t(loff_t, len, isize - *ppos);
                         n = splice_folio_into_pipe(pipe, folio, *ppos, n);
                         if (!n)
                                 goto out;
                         len -= n;
                         total_spliced += n;
                         *ppos += n;
                         in->f_ra.prev_pos = *ppos;
                         if (pipe_full(pipe->head, pipe->tail, pipe->max_usage))
                                 goto out;
                 }
 
                 folio_batch_release(&fbatch);
         } while (len);
 
 out:
         folio_batch_release(&fbatch);
         file_accessed(in);
 
         return total_spliced ? total_spliced : error;
 }
 EXPORT_SYMBOL(filemap_splice_read);
 
 static inline loff_t folio_seek_hole_data(struct xa_state *xas,
                 struct address_space *mapping, struct folio *folio,
                 loff_t start, loff_t end, bool seek_data)
 {
         const struct address_space_operations *ops = mapping->a_ops;
         size_t offset, bsz = i_blocksize(mapping->host);
 
         if (xa_is_value(folio) || folio_test_uptodate(folio))
                 return seek_data ? start : end;
         if (!ops->is_partially_uptodate)
                 return seek_data ? end : start;
 
         xas_pause(xas);
         rcu_read_unlock();
         folio_lock(folio);
         if (unlikely(folio->mapping != mapping))
                 goto unlock;
 
         offset = offset_in_folio(folio, start) & ~(bsz - 1);
 
         do {
                 if (ops->is_partially_uptodate(folio, offset, bsz) ==
                                                         seek_data)
                         break;
                 start = (start + bsz) & ~(bsz - 1);
                 offset += bsz;
         } while (offset < folio_size(folio));
 unlock:
         folio_unlock(folio);
         rcu_read_lock();
         return start;
 }
 
 static inline size_t seek_folio_size(struct xa_state *xas, struct folio *folio)
 {
         if (xa_is_value(folio))
                 return PAGE_SIZE << xa_get_order(xas->xa, xas->xa_index);
         return folio_size(folio);
 }
 
 /**
  * mapping_seek_hole_data - Seek for SEEK_DATA / SEEK_HOLE in the page cache.
  * @mapping: Address space to search.
  * @start: First byte to consider.
  * @end: Limit of search (exclusive).
  * @whence: Either SEEK_HOLE or SEEK_DATA.
  *
  * If the page cache knows which blocks contain holes and which blocks
  * contain data, your filesystem can use this function to implement
  * SEEK_HOLE and SEEK_DATA.  This is useful for filesystems which are
  * entirely memory-based such as tmpfs, and filesystems which support
  * unwritten extents.
  *
  * Return: The requested offset on success, or -ENXIO if @whence specifies
  * SEEK_DATA and there is no data after @start.  There is an implicit hole
  * after @end - 1, so SEEK_HOLE returns @end if all the bytes between @start
  * and @end contain data.
  */
 loff_t mapping_seek_hole_data(struct address_space *mapping, loff_t start,
                 loff_t end, int whence)
 {
         XA_STATE(xas, &mapping->i_pages, start >> PAGE_SHIFT);
         pgoff_t max = (end - 1) >> PAGE_SHIFT;
         bool seek_data = (whence == SEEK_DATA);
         struct folio *folio;
 
         if (end <= start)
                 return -ENXIO;
 
         rcu_read_lock();
         while ((folio = find_get_entry(&xas, max, XA_PRESENT))) {
                 loff_t pos = (u64)xas.xa_index << PAGE_SHIFT;
                 size_t seek_size;
 
                 if (start < pos) {
                         if (!seek_data)
                                 goto unlock;
                         start = pos;
                 }
 
                 seek_size = seek_folio_size(&xas, folio);
                 pos = round_up((u64)pos + 1, seek_size);
                 start = folio_seek_hole_data(&xas, mapping, folio, start, pos,
                                 seek_data);
                 if (start < pos)
                         goto unlock;
                 if (start >= end)
                         break;
                 if (seek_size > PAGE_SIZE)
                         xas_set(&xas, pos >> PAGE_SHIFT);
                 if (!xa_is_value(folio))
                         folio_put(folio);
         }
         if (seek_data)
                 start = -ENXIO;
 unlock:
         rcu_read_unlock();
         if (folio && !xa_is_value(folio))
                 folio_put(folio);
         if (start > end)
                 return end;
         return start;
 }
 
 #ifdef CONFIG_MMU
 #define MMAP_LOTSAMISS  (100)
 /*
  * lock_folio_maybe_drop_mmap - lock the page, possibly dropping the mmap_lock
  * @vmf - the vm_fault for this fault.
  * @folio - the folio to lock.
  * @fpin - the pointer to the file we may pin (or is already pinned).
  *
  * This works similar to lock_folio_or_retry in that it can drop the
  * mmap_lock.  It differs in that it actually returns the folio locked
  * if it returns 1 and 0 if it couldn't lock the folio.  If we did have
  * to drop the mmap_lock then fpin will point to the pinned file and
  * needs to be fput()'ed at a later point.
  */
 static int lock_folio_maybe_drop_mmap(struct vm_fault *vmf, struct folio *folio,
                                      struct file **fpin)
 {
         if (folio_trylock(folio))
                 return 1;
 
         /*
          * NOTE! This will make us return with VM_FAULT_RETRY, but with
          * the fault lock still held. That's how FAULT_FLAG_RETRY_NOWAIT
          * is supposed to work. We have way too many special cases..
          */
         if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT)
                 return 0;
 
         *fpin = maybe_unlock_mmap_for_io(vmf, *fpin);
         if (vmf->flags & FAULT_FLAG_KILLABLE) {
                 if (__folio_lock_killable(folio)) {
                         /*
                          * We didn't have the right flags to drop the
                          * fault lock, but all fault_handlers only check
                          * for fatal signals if we return VM_FAULT_RETRY,
                          * so we need to drop the fault lock here and
                          * return 0 if we don't have a fpin.
                          */
                         if (*fpin == NULL)
                                 release_fault_lock(vmf);
                         return 0;
                 }
         } else
                 __folio_lock(folio);
 
         return 1;
 }
 
 /*
  * Synchronous readahead happens when we don't even find a page in the page
  * cache at all.  We don't want to perform IO under the mmap sem, so if we have
  * to drop the mmap sem we return the file that was pinned in order for us to do
  * that.  If we didn't pin a file then we return NULL.  The file that is
  * returned needs to be fput()'ed when we're done with it.
  */
 static struct file *do_sync_mmap_readahead(struct vm_fault *vmf)
 {
         struct file *file = vmf->vma->vm_file;
         struct file_ra_state *ra = &file->f_ra;
         struct address_space *mapping = file->f_mapping;
         DEFINE_READAHEAD(ractl, file, ra, mapping, vmf->pgoff);
         struct file *fpin = NULL;
         unsigned long vm_flags = vmf->vma->vm_flags;
         unsigned int mmap_miss;
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
         /* Use the readahead code, even if readahead is disabled */
         if ((vm_flags & VM_HUGEPAGE) && HPAGE_PMD_ORDER <= MAX_PAGECACHE_ORDER) {
                 fpin = maybe_unlock_mmap_for_io(vmf, fpin);
                 ractl._index &= ~((unsigned long)HPAGE_PMD_NR - 1);
                 ra->size = HPAGE_PMD_NR;
                 /*
                  * Fetch two PMD folios, so we get the chance to actually
                  * readahead, unless we've been told not to.
                  */
                 if (!(vm_flags & VM_RAND_READ))
                         ra->size *= 2;
                 ra->async_size = HPAGE_PMD_NR;
                 page_cache_ra_order(&ractl, ra, HPAGE_PMD_ORDER);
                 return fpin;
         }
 #endif
 
         /* If we don't want any read-ahead, don't bother */
         if (vm_flags & VM_RAND_READ)
                 return fpin;
         if (!ra->ra_pages)
                 return fpin;
 
         if (vm_flags & VM_SEQ_READ) {
                 fpin = maybe_unlock_mmap_for_io(vmf, fpin);
                 page_cache_sync_ra(&ractl, ra->ra_pages);
                 return fpin;
         }
 
         /* Avoid banging the cache line if not needed */
         mmap_miss = READ_ONCE(ra->mmap_miss);
         if (mmap_miss < MMAP_LOTSAMISS * 10)
                 WRITE_ONCE(ra->mmap_miss, ++mmap_miss);
 
         /*
          * Do we miss much more than hit in this file? If so,
          * stop bothering with read-ahead. It will only hurt.
          */
         if (mmap_miss > MMAP_LOTSAMISS)
                 return fpin;
 
         /*
          * mmap read-around
          */
         fpin = maybe_unlock_mmap_for_io(vmf, fpin);
         ra->start = max_t(long, 0, vmf->pgoff - ra->ra_pages / 2);
         ra->size = ra->ra_pages;
         ra->async_size = ra->ra_pages / 4;
         ractl._index = ra->start;
         page_cache_ra_order(&ractl, ra, 0);
         return fpin;
 }
 
 /*
  * Asynchronous readahead happens when we find the page and PG_readahead,
  * so we want to possibly extend the readahead further.  We return the file that
  * was pinned if we have to drop the mmap_lock in order to do IO.
  */
 static struct file *do_async_mmap_readahead(struct vm_fault *vmf,
                                             struct folio *folio)
 {
         struct file *file = vmf->vma->vm_file;
         struct file_ra_state *ra = &file->f_ra;
         DEFINE_READAHEAD(ractl, file, ra, file->f_mapping, vmf->pgoff);
         struct file *fpin = NULL;
         unsigned int mmap_miss;
 
         /* If we don't want any read-ahead, don't bother */
         if (vmf->vma->vm_flags & VM_RAND_READ || !ra->ra_pages)
                 return fpin;
 
         mmap_miss = READ_ONCE(ra->mmap_miss);
         if (mmap_miss)
                 WRITE_ONCE(ra->mmap_miss, --mmap_miss);
 
         if (folio_test_readahead(folio)) {
                 fpin = maybe_unlock_mmap_for_io(vmf, fpin);
                 page_cache_async_ra(&ractl, folio, ra->ra_pages);
         }
         return fpin;
 }
 
 static vm_fault_t filemap_fault_recheck_pte_none(struct vm_fault *vmf)
 {
         struct vm_area_struct *vma = vmf->vma;
         vm_fault_t ret = 0;
         pte_t *ptep;
 
         /*
          * We might have COW'ed a pagecache folio and might now have an mlocked
          * anon folio mapped. The original pagecache folio is not mlocked and
          * might have been evicted. During a read+clear/modify/write update of
          * the PTE, such as done in do_numa_page()/change_pte_range(), we
          * temporarily clear the PTE under PT lock and might detect it here as
          * "none" when not holding the PT lock.
          *
          * Not rechecking the PTE under PT lock could result in an unexpected
          * major fault in an mlock'ed region. Recheck only for this special
          * scenario while holding the PT lock, to not degrade non-mlocked
          * scenarios. Recheck the PTE without PT lock firstly, thereby reducing
          * the number of times we hold PT lock.
          */
         if (!(vma->vm_flags & VM_LOCKED))
                 return 0;
 
         if (!(vmf->flags & FAULT_FLAG_ORIG_PTE_VALID))
                 return 0;
 
         ptep = pte_offset_map_nolock(vma->vm_mm, vmf->pmd, vmf->address,
                                      &vmf->ptl);
         if (unlikely(!ptep))
                 return VM_FAULT_NOPAGE;
 
         if (unlikely(!pte_none(ptep_get_lockless(ptep)))) {
                 ret = VM_FAULT_NOPAGE;
         } else {
                 spin_lock(vmf->ptl);
                 if (unlikely(!pte_none(ptep_get(ptep))))
                         ret = VM_FAULT_NOPAGE;
                 spin_unlock(vmf->ptl);
         }
         pte_unmap(ptep);
         return ret;
 }
 
 /**
  * filemap_fault - read in file data for page fault handling
  * @vmf:        struct vm_fault containing details of the fault
  *
  * filemap_fault() is invoked via the vma operations vector for a
  * mapped memory region to read in file data during a page fault.
  *
  * The goto's are kind of ugly, but this streamlines the normal case of having
  * it in the page cache, and handles the special cases reasonably without
  * having a lot of duplicated code.
  *
  * vma->vm_mm->mmap_lock must be held on entry.
  *
  * If our return value has VM_FAULT_RETRY set, it's because the mmap_lock
  * may be dropped before doing I/O or by lock_folio_maybe_drop_mmap().
  *
  * If our return value does not have VM_FAULT_RETRY set, the mmap_lock
  * has not been released.
  *
  * We never return with VM_FAULT_RETRY and a bit from VM_FAULT_ERROR set.
  *
  * Return: bitwise-OR of %VM_FAULT_ codes.
  */
 vm_fault_t filemap_fault(struct vm_fault *vmf)
 {
         int error;
         struct file *file = vmf->vma->vm_file;
         struct file *fpin = NULL;
         struct address_space *mapping = file->f_mapping;
         struct inode *inode = mapping->host;
         pgoff_t max_idx, index = vmf->pgoff;
         struct folio *folio;
         vm_fault_t ret = 0;
         bool mapping_locked = false;
 
         max_idx = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
         if (unlikely(index >= max_idx))
                 return VM_FAULT_SIGBUS;
 
         /*
          * Do we have something in the page cache already?
          */
         folio = filemap_get_folio(mapping, index);
         if (likely(!IS_ERR(folio))) {
                 /*
                  * We found the page, so try async readahead before waiting for
                  * the lock.
                  */
                 if (!(vmf->flags & FAULT_FLAG_TRIED))
                         fpin = do_async_mmap_readahead(vmf, folio);
                 if (unlikely(!folio_test_uptodate(folio))) {
                         filemap_invalidate_lock_shared(mapping);
                         mapping_locked = true;
                 }
         } else {
                 ret = filemap_fault_recheck_pte_none(vmf);
                 if (unlikely(ret))
                         return ret;
 
                 /* No page in the page cache at all */
                 count_vm_event(PGMAJFAULT);
                 count_memcg_event_mm(vmf->vma->vm_mm, PGMAJFAULT);
                 ret = VM_FAULT_MAJOR;
                 fpin = do_sync_mmap_readahead(vmf);
 retry_find:
                 /*
                  * See comment in filemap_create_folio() why we need
                  * invalidate_lock
                  */
                 if (!mapping_locked) {
                         filemap_invalidate_lock_shared(mapping);
                         mapping_locked = true;
                 }
                 folio = __filemap_get_folio(mapping, index,
                                           FGP_CREAT|FGP_FOR_MMAP,
                                           vmf->gfp_mask);
                 if (IS_ERR(folio)) {
                         if (fpin)
                                 goto out_retry;
                         filemap_invalidate_unlock_shared(mapping);
                         return VM_FAULT_OOM;
                 }
         }
 
         if (!lock_folio_maybe_drop_mmap(vmf, folio, &fpin))
                 goto out_retry;
 
         /* Did it get truncated? */
         if (unlikely(folio->mapping != mapping)) {
                 folio_unlock(folio);
                 folio_put(folio);
                 goto retry_find;
         }
         VM_BUG_ON_FOLIO(!folio_contains(folio, index), folio);
 
         /*
          * We have a locked folio in the page cache, now we need to check
          * that it's up-to-date. If not, it is going to be due to an error,
          * or because readahead was otherwise unable to retrieve it.
          */
         if (unlikely(!folio_test_uptodate(folio))) {
                 /*
                  * If the invalidate lock is not held, the folio was in cache
                  * and uptodate and now it is not. Strange but possible since we
                  * didn't hold the page lock all the time. Let's drop
                  * everything, get the invalidate lock and try again.
                  */
                 if (!mapping_locked) {
                         folio_unlock(folio);
                         folio_put(folio);
                         goto retry_find;
                 }
 
                 /*
                  * OK, the folio is really not uptodate. This can be because the
                  * VMA has the VM_RAND_READ flag set, or because an error
                  * arose. Let's read it in directly.
                  */
                 goto page_not_uptodate;
         }
 
         /*
          * We've made it this far and we had to drop our mmap_lock, now is the
          * time to return to the upper layer and have it re-find the vma and
          * redo the fault.
          */
         if (fpin) {
                 folio_unlock(folio);
                 goto out_retry;
         }
         if (mapping_locked)
                 filemap_invalidate_unlock_shared(mapping);
 
         /*
          * Found the page and have a reference on it.
          * We must recheck i_size under page lock.
          */
         max_idx = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
         if (unlikely(index >= max_idx)) {
                 folio_unlock(folio);
                 folio_put(folio);
                 return VM_FAULT_SIGBUS;
         }
 
         vmf->page = folio_file_page(folio, index);
         return ret | VM_FAULT_LOCKED;
 
 page_not_uptodate:
         /*
          * Umm, take care of errors if the page isn't up-to-date.
          * Try to re-read it _once_. We do this synchronously,
          * because there really aren't any performance issues here
          * and we need to check for errors.
          */
         fpin = maybe_unlock_mmap_for_io(vmf, fpin);
         error = filemap_read_folio(file, mapping->a_ops->read_folio, folio);
         if (fpin)
                 goto out_retry;
         folio_put(folio);
 
         if (!error || error == AOP_TRUNCATED_PAGE)
                 goto retry_find;
         filemap_invalidate_unlock_shared(mapping);
 
         return VM_FAULT_SIGBUS;
 
 out_retry:
         /*
          * We dropped the mmap_lock, we need to return to the fault handler to
          * re-find the vma and come back and find our hopefully still populated
          * page.
          */
         if (!IS_ERR(folio))
                 folio_put(folio);
         if (mapping_locked)
                 filemap_invalidate_unlock_shared(mapping);
         if (fpin)
                 fput(fpin);
         return ret | VM_FAULT_RETRY;
 }
 EXPORT_SYMBOL(filemap_fault);
 
 static bool filemap_map_pmd(struct vm_fault *vmf, struct folio *folio,
                 pgoff_t start)
 {
         struct mm_struct *mm = vmf->vma->vm_mm;
 
         /* Huge page is mapped? No need to proceed. */
         if (pmd_trans_huge(*vmf->pmd)) {
                 folio_unlock(folio);
                 folio_put(folio);
                 return true;
         }
 
         if (pmd_none(*vmf->pmd) && folio_test_pmd_mappable(folio)) {
                 struct page *page = folio_file_page(folio, start);
                 vm_fault_t ret = do_set_pmd(vmf, page);
                 if (!ret) {
                         /* The page is mapped successfully, reference consumed. */
                         folio_unlock(folio);
                         return true;
                 }
         }
 
         if (pmd_none(*vmf->pmd) && vmf->prealloc_pte)
                 pmd_install(mm, vmf->pmd, &vmf->prealloc_pte);
 
         return false;
 }
 
 static struct folio *next_uptodate_folio(struct xa_state *xas,
                 struct address_space *mapping, pgoff_t end_pgoff)
 {
         struct folio *folio = xas_next_entry(xas, end_pgoff);
         unsigned long max_idx;
 
         do {
                 if (!folio)
                         return NULL;
                 if (xas_retry(xas, folio))
                         continue;
                 if (xa_is_value(folio))
                         continue;
                 if (folio_test_locked(folio))
                         continue;
                 if (!folio_try_get(folio))
                         continue;
                 /* Has the page moved or been split? */
                 if (unlikely(folio != xas_reload(xas)))
                         goto skip;
                 if (!folio_test_uptodate(folio) || folio_test_readahead(folio))
                         goto skip;
                 if (!folio_trylock(folio))
                         goto skip;
                 if (folio->mapping != mapping)
                         goto unlock;
                 if (!folio_test_uptodate(folio))
                         goto unlock;
                 max_idx = DIV_ROUND_UP(i_size_read(mapping->host), PAGE_SIZE);
                 if (xas->xa_index >= max_idx)
                         goto unlock;
                 return folio;
 unlock:
                 folio_unlock(folio);
 skip:
                 folio_put(folio);
         } while ((folio = xas_next_entry(xas, end_pgoff)) != NULL);
 
         return NULL;
 }
 
 /*
  * Map page range [start_page, start_page + nr_pages) of folio.
  * start_page is gotten from start by folio_page(folio, start)
  */
 static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
                         struct folio *folio, unsigned long start,
                         unsigned long addr, unsigned int nr_pages,
                         unsigned long *rss, unsigned int *mmap_miss)
 {
         vm_fault_t ret = 0;
         struct page *page = folio_page(folio, start);
         unsigned int count = 0;
         pte_t *old_ptep = vmf->pte;
 
         do {
                 if (PageHWPoison(page + count))
                         goto skip;
 
                 /*
                  * If there are too many folios that are recently evicted
                  * in a file, they will probably continue to be evicted.
                  * In such situation, read-ahead is only a waste of IO.
                  * Don't decrease mmap_miss in this scenario to make sure
                  * we can stop read-ahead.
                  */
                 if (!folio_test_workingset(folio))
                         (*mmap_miss)++;
 
                 /*
                  * NOTE: If there're PTE markers, we'll leave them to be
                  * handled in the specific fault path, and it'll prohibit the
                  * fault-around logic.
                  */
                 if (!pte_none(ptep_get(&vmf->pte[count])))
                         goto skip;
 
                 count++;
                 continue;
 skip:
                 if (count) {
                         set_pte_range(vmf, folio, page, count, addr);
                         *rss += count;
                         folio_ref_add(folio, count);
                         if (in_range(vmf->address, addr, count * PAGE_SIZE))
                                 ret = VM_FAULT_NOPAGE;
                 }
 
                 count++;
                 page += count;
                 vmf->pte += count;
                 addr += count * PAGE_SIZE;
                 count = 0;
         } while (--nr_pages > 0);
 
         if (count) {
                 set_pte_range(vmf, folio, page, count, addr);
                 *rss += count;
                 folio_ref_add(folio, count);
                 if (in_range(vmf->address, addr, count * PAGE_SIZE))
                         ret = VM_FAULT_NOPAGE;
         }
 
         vmf->pte = old_ptep;
 
         return ret;
 }
 
 static vm_fault_t filemap_map_order0_folio(struct vm_fault *vmf,
                 struct folio *folio, unsigned long addr,
                 unsigned long *rss, unsigned int *mmap_miss)
 {
         vm_fault_t ret = 0;
         struct page *page = &folio->page;
 
         if (PageHWPoison(page))
                 return ret;
 
         /* See comment of filemap_map_folio_range() */
         if (!folio_test_workingset(folio))
                 (*mmap_miss)++;
 
         /*
          * NOTE: If there're PTE markers, we'll leave them to be
          * handled in the specific fault path, and it'll prohibit
          * the fault-around logic.
          */
         if (!pte_none(ptep_get(vmf->pte)))
                 return ret;
 
         if (vmf->address == addr)
                 ret = VM_FAULT_NOPAGE;
 
         set_pte_range(vmf, folio, page, 1, addr);
         (*rss)++;
         folio_ref_inc(folio);
 
         return ret;
 }
 
 vm_fault_t filemap_map_pages(struct vm_fault *vmf,
                              pgoff_t start_pgoff, pgoff_t end_pgoff)
 {
         struct vm_area_struct *vma = vmf->vma;
         struct file *file = vma->vm_file;
         struct address_space *mapping = file->f_mapping;
         pgoff_t last_pgoff = start_pgoff;
         unsigned long addr;
         XA_STATE(xas, &mapping->i_pages, start_pgoff);
         struct folio *folio;
         vm_fault_t ret = 0;
         unsigned long rss = 0;
         unsigned int nr_pages = 0, mmap_miss = 0, mmap_miss_saved, folio_type;
 
         rcu_read_lock();
         folio = next_uptodate_folio(&xas, mapping, end_pgoff);
         if (!folio)
                 goto out;
 
         if (filemap_map_pmd(vmf, folio, start_pgoff)) {
                 ret = VM_FAULT_NOPAGE;
                 goto out;
         }
 
         addr = vma->vm_start + ((start_pgoff - vma->vm_pgoff) << PAGE_SHIFT);
         vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, addr, &vmf->ptl);
         if (!vmf->pte) {
                 folio_unlock(folio);
                 folio_put(folio);
                 goto out;
         }
 
         folio_type = mm_counter_file(folio);
         do {
                 unsigned long end;
 
                 addr += (xas.xa_index - last_pgoff) << PAGE_SHIFT;
                 vmf->pte += xas.xa_index - last_pgoff;
                 last_pgoff = xas.xa_index;
                 end = folio_next_index(folio) - 1;
                 nr_pages = min(end, end_pgoff) - xas.xa_index + 1;
 
                 if (!folio_test_large(folio))
                         ret |= filemap_map_order0_folio(vmf,
                                         folio, addr, &rss, &mmap_miss);
                 else
                         ret |= filemap_map_folio_range(vmf, folio,
                                         xas.xa_index - folio->index, addr,
                                         nr_pages, &rss, &mmap_miss);
 
                 folio_unlock(folio);
                 folio_put(folio);
         } while ((folio = next_uptodate_folio(&xas, mapping, end_pgoff)) != NULL);
         add_mm_counter(vma->vm_mm, folio_type, rss);
         pte_unmap_unlock(vmf->pte, vmf->ptl);
 out:
         rcu_read_unlock();
 
         mmap_miss_saved = READ_ONCE(file->f_ra.mmap_miss);
         if (mmap_miss >= mmap_miss_saved)
                 WRITE_ONCE(file->f_ra.mmap_miss, 0);
         else
                 WRITE_ONCE(file->f_ra.mmap_miss, mmap_miss_saved - mmap_miss);
 
         return ret;
 }
 EXPORT_SYMBOL(filemap_map_pages);
 
 vm_fault_t filemap_page_mkwrite(struct vm_fault *vmf)
 {
         struct address_space *mapping = vmf->vma->vm_file->f_mapping;
         struct folio *folio = page_folio(vmf->page);
         vm_fault_t ret = VM_FAULT_LOCKED;
 
         sb_start_pagefault(mapping->host->i_sb);
         file_update_time(vmf->vma->vm_file);
         folio_lock(folio);
         if (folio->mapping != mapping) {
                 folio_unlock(folio);
                 ret = VM_FAULT_NOPAGE;
                 goto out;
         }
         /*
          * We mark the folio dirty already here so that when freeze is in
          * progress, we are guaranteed that writeback during freezing will
          * see the dirty folio and writeprotect it again.
          */
         folio_mark_dirty(folio);
         folio_wait_stable(folio);
 out:
         sb_end_pagefault(mapping->host->i_sb);
         return ret;
 }
 
 const struct vm_operations_struct generic_file_vm_ops = {
         .fault          = filemap_fault,
         .map_pages      = filemap_map_pages,
         .page_mkwrite   = filemap_page_mkwrite,
 };
 
 /* This is used for a general mmap of a disk file */
 
 int generic_file_mmap(struct file *file, struct vm_area_struct *vma)
 {
         struct address_space *mapping = file->f_mapping;
 
         if (!mapping->a_ops->read_folio)
                 return -ENOEXEC;
         file_accessed(file);
         vma->vm_ops = &generic_file_vm_ops;
         return 0;
 }
 
 /*
  * This is for filesystems which do not implement ->writepage.
  */
 int generic_file_readonly_mmap(struct file *file, struct vm_area_struct *vma)
 {
         if (vma_is_shared_maywrite(vma))
                 return -EINVAL;
         return generic_file_mmap(file, vma);
 }
 #else
 vm_fault_t filemap_page_mkwrite(struct vm_fault *vmf)
 {
         return VM_FAULT_SIGBUS;
 }
 int generic_file_mmap(struct file *file, struct vm_area_struct *vma)
 {
         return -ENOSYS;
 }
 int generic_file_readonly_mmap(struct file *file, struct vm_area_struct *vma)
 {
         return -ENOSYS;
 }
 #endif /* CONFIG_MMU */
 
 EXPORT_SYMBOL(filemap_page_mkwrite);
 EXPORT_SYMBOL(generic_file_mmap);
 EXPORT_SYMBOL(generic_file_readonly_mmap);
 
 static struct folio *do_read_cache_folio(struct address_space *mapping,
                 pgoff_t index, filler_t filler, struct file *file, gfp_t gfp)
 {
         struct folio *folio;
         int err;
 
         if (!filler)
                 filler = mapping->a_ops->read_folio;
 repeat:
         folio = filemap_get_folio(mapping, index);
         if (IS_ERR(folio)) {
                 folio = filemap_alloc_folio(gfp, 0);
                 if (!folio)
                         return ERR_PTR(-ENOMEM);
                 err = filemap_add_folio(mapping, folio, index, gfp);
                 if (unlikely(err)) {
                         folio_put(folio);
                         if (err == -EEXIST)
                                 goto repeat;
                         /* Presumably ENOMEM for xarray node */
                         return ERR_PTR(err);
                 }
 
                 goto filler;
         }
         if (folio_test_uptodate(folio))
                 goto out;
 
         if (!folio_trylock(folio)) {
                 folio_put_wait_locked(folio, TASK_UNINTERRUPTIBLE);
                 goto repeat;
         }
 
         /* Folio was truncated from mapping */
         if (!folio->mapping) {
                 folio_unlock(folio);
                 folio_put(folio);
                 goto repeat;
         }
 
         /* Someone else locked and filled the page in a very small window */
         if (folio_test_uptodate(folio)) {
                 folio_unlock(folio);
                 goto out;
         }
 
 filler:
         err = filemap_read_folio(file, filler, folio);
         if (err) {
                 folio_put(folio);
                 if (err == AOP_TRUNCATED_PAGE)
                         goto repeat;
                 return ERR_PTR(err);
         }
 
 out:
         folio_mark_accessed(folio);
         return folio;
 }
 
 /**
  * read_cache_folio - Read into page cache, fill it if needed.
  * @mapping: The address_space to read from.
  * @index: The index to read.
  * @filler: Function to perform the read, or NULL to use aops->read_folio().
  * @file: Passed to filler function, may be NULL if not required.
  *
  * Read one page into the page cache.  If it succeeds, the folio returned
  * will contain @index, but it may not be the first page of the folio.
  *
  * If the filler function returns an error, it will be returned to the
  * caller.
  *
  * Context: May sleep.  Expects mapping->invalidate_lock to be held.
  * Return: An uptodate folio on success, ERR_PTR() on failure.
  */
 struct folio *read_cache_folio(struct address_space *mapping, pgoff_t index,
                 filler_t filler, struct file *file)
 {
         return do_read_cache_folio(mapping, index, filler, file,
                         mapping_gfp_mask(mapping));
 }
 EXPORT_SYMBOL(read_cache_folio);
 
 /**
  * mapping_read_folio_gfp - Read into page cache, using specified allocation flags.
  * @mapping:    The address_space for the folio.
  * @index:      The index that the allocated folio will contain.
  * @gfp:        The page allocator flags to use if allocating.
  *
  * This is the same as "read_cache_folio(mapping, index, NULL, NULL)", but with
  * any new memory allocations done using the specified allocation flags.
  *
  * The most likely error from this function is EIO, but ENOMEM is
  * possible and so is EINTR.  If ->read_folio returns another error,
  * that will be returned to the caller.
  *
  * The function expects mapping->invalidate_lock to be already held.
  *
  * Return: Uptodate folio on success, ERR_PTR() on failure.
  */
 struct folio *mapping_read_folio_gfp(struct address_space *mapping,
                 pgoff_t index, gfp_t gfp)
 {
         return do_read_cache_folio(mapping, index, NULL, NULL, gfp);
 }
 EXPORT_SYMBOL(mapping_read_folio_gfp);
 
 static struct page *do_read_cache_page(struct address_space *mapping,
                 pgoff_t index, filler_t *filler, struct file *file, gfp_t gfp)
 {
         struct folio *folio;
 
         folio = do_read_cache_folio(mapping, index, filler, file, gfp);
         if (IS_ERR(folio))
                 return &folio->page;
         return folio_file_page(folio, index);
 }
 
 struct page *read_cache_page(struct address_space *mapping,
                         pgoff_t index, filler_t *filler, struct file *file)
 {
         return do_read_cache_page(mapping, index, filler, file,
                         mapping_gfp_mask(mapping));
 }
 EXPORT_SYMBOL(read_cache_page);
 
 /**
  * read_cache_page_gfp - read into page cache, using specified page allocation flags.
  * @mapping:    the page's address_space
  * @index:      the page index
  * @gfp:        the page allocator flags to use if allocating
  *
  * This is the same as "read_mapping_page(mapping, index, NULL)", but with
  * any new page allocations done using the specified allocation flags.
  *
  * If the page does not get brought uptodate, return -EIO.
  *
  * The function expects mapping->invalidate_lock to be already held.
  *
  * Return: up to date page on success, ERR_PTR() on failure.
  */
 struct page *read_cache_page_gfp(struct address_space *mapping,
                                 pgoff_t index,
                                 gfp_t gfp)
 {
         return do_read_cache_page(mapping, index, NULL, NULL, gfp);
 }
 EXPORT_SYMBOL(read_cache_page_gfp);
 
 /*
  * Warn about a page cache invalidation failure during a direct I/O write.
  */
 static void dio_warn_stale_pagecache(struct file *filp)
 {
         static DEFINE_RATELIMIT_STATE(_rs, 86400 * HZ, DEFAULT_RATELIMIT_BURST);
         char pathname[128];
         char *path;
 
         errseq_set(&filp->f_mapping->wb_err, -EIO);
         if (__ratelimit(&_rs)) {
                 path = file_path(filp, pathname, sizeof(pathname));
                 if (IS_ERR(path))
                         path = "(unknown)";
                 pr_crit("Page cache invalidation failure on direct I/O.  Possible data corruption due to collision with buffered I/O!\n");
                 pr_crit("File: %s PID: %d Comm: %.20s\n", path, current->pid,
                         current->comm);
         }
 }
 
 void kiocb_invalidate_post_direct_write(struct kiocb *iocb, size_t count)
 {
         struct address_space *mapping = iocb->ki_filp->f_mapping;
 
         if (mapping->nrpages &&
             invalidate_inode_pages2_range(mapping,
                         iocb->ki_pos >> PAGE_SHIFT,
                         (iocb->ki_pos + count - 1) >> PAGE_SHIFT))
                 dio_warn_stale_pagecache(iocb->ki_filp);
 }
 
 ssize_t
 generic_file_direct_write(struct kiocb *iocb, struct iov_iter *from)
 {
         struct address_space *mapping = iocb->ki_filp->f_mapping;
         size_t write_len = iov_iter_count(from);
         ssize_t written;
 
         /*
          * If a page can not be invalidated, return 0 to fall back
          * to buffered write.
          */
         written = kiocb_invalidate_pages(iocb, write_len);
         if (written) {
                 if (written == -EBUSY)
                         return 0;
                 return written;
         }
 
         written = mapping->a_ops->direct_IO(iocb, from);
 
         /*
          * Finally, try again to invalidate clean pages which might have been
          * cached by non-direct readahead, or faulted in by get_user_pages()
          * if the source of the write was an mmap'ed region of the file
          * we're writing.  Either one is a pretty crazy thing to do,
          * so we don't support it 100%.  If this invalidation
          * fails, tough, the write still worked...
          *
          * Most of the time we do not need this since dio_complete() will do
          * the invalidation for us. However there are some file systems that
          * do not end up with dio_complete() being called, so let's not break
          * them by removing it completely.
          *
          * Noticeable example is a blkdev_direct_IO().
          *
          * Skip invalidation for async writes or if mapping has no pages.
          */
         if (written > 0) {
                 struct inode *inode = mapping->host;
                 loff_t pos = iocb->ki_pos;
 
                 kiocb_invalidate_post_direct_write(iocb, written);
                 pos += written;
                 write_len -= written;
                 if (pos > i_size_read(inode) && !S_ISBLK(inode->i_mode)) {
                         i_size_write(inode, pos);
                         mark_inode_dirty(inode);
                 }
                 iocb->ki_pos = pos;
         }
         if (written != -EIOCBQUEUED)
                 iov_iter_revert(from, write_len - iov_iter_count(from));
         return written;
 }
 EXPORT_SYMBOL(generic_file_direct_write);
 
 ssize_t generic_perform_write(struct kiocb *iocb, struct iov_iter *i)
 {
         struct file *file = iocb->ki_filp;
         loff_t pos = iocb->ki_pos;
         struct address_space *mapping = file->f_mapping;
         const struct address_space_operations *a_ops = mapping->a_ops;
         size_t chunk = mapping_max_folio_size(mapping);
         long status = 0;
         ssize_t written = 0;
 
         do {
                 struct page *page;
                 struct folio *folio;
                 size_t offset;          /* Offset into folio */
                 size_t bytes;           /* Bytes to write to folio */
                 size_t copied;          /* Bytes copied from user */
                 void *fsdata = NULL;
 
                 bytes = iov_iter_count(i);
 retry:
                 offset = pos & (chunk - 1);
                 bytes = min(chunk - offset, bytes);
                 balance_dirty_pages_ratelimited(mapping);
 
                 /*
                  * Bring in the user page that we will copy from _first_.
                  * Otherwise there's a nasty deadlock on copying from the
                  * same page as we're writing to, without it being marked
                  * up-to-date.
                  */
                 if (unlikely(fault_in_iov_iter_readable(i, bytes) == bytes)) {
                         status = -EFAULT;
                         break;
                 }
 
                 if (fatal_signal_pending(current)) {
                         status = -EINTR;
                         break;
                 }
 
                 status = a_ops->write_begin(file, mapping, pos, bytes,
                                                 &page, &fsdata);
                 if (unlikely(status < 0))
                         break;
 
                 folio = page_folio(page);
                 offset = offset_in_folio(folio, pos);
                 if (bytes > folio_size(folio) - offset)
                         bytes = folio_size(folio) - offset;
 
                 if (mapping_writably_mapped(mapping))
                         flush_dcache_folio(folio);
 
                 copied = copy_folio_from_iter_atomic(folio, offset, bytes, i);
                 flush_dcache_folio(folio);
 
                 status = a_ops->write_end(file, mapping, pos, bytes, copied,
                                                 page, fsdata);
                 if (unlikely(status != copied)) {
                         iov_iter_revert(i, copied - max(status, 0L));
                         if (unlikely(status < 0))
                                 break;
                 }
                 cond_resched();
 
                 if (unlikely(status == 0)) {
                         /*
                          * A short copy made ->write_end() reject the
                          * thing entirely.  Might be memory poisoning
                          * halfway through, might be a race with munmap,
                          * might be severe memory pressure.
                          */
                         if (chunk > PAGE_SIZE)
                                 chunk /= 2;
                         if (copied) {
                                 bytes = copied;
                                 goto retry;
                         }
                 } else {
                         pos += status;
                         written += status;
                 }
         } while (iov_iter_count(i));
 
         if (!written)
                 return status;
         iocb->ki_pos += written;
         return written;
 }
 EXPORT_SYMBOL(generic_perform_write);
 
 /**
  * __generic_file_write_iter - write data to a file
  * @iocb:       IO state structure (file, offset, etc.)
  * @from:       iov_iter with data to write
  *
  * This function does all the work needed for actually writing data to a
  * file. It does all basic checks, removes SUID from the file, updates
  * modification times and calls proper subroutines depending on whether we
  * do direct IO or a standard buffered write.
  *
  * It expects i_rwsem to be grabbed unless we work on a block device or similar
  * object which does not need locking at all.
  *
  * This function does *not* take care of syncing data in case of O_SYNC write.
  * A caller has to handle it. This is mainly due to the fact that we want to
  * avoid syncing under i_rwsem.
  *
  * Return:
  * * number of bytes written, even for truncated writes
  * * negative error code if no data has been written at all
  */
 ssize_t __generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 {
         struct file *file = iocb->ki_filp;
         struct address_space *mapping = file->f_mapping;
         struct inode *inode = mapping->host;
         ssize_t ret;
 
         ret = file_remove_privs(file);
         if (ret)
                 return ret;
 
         ret = file_update_time(file);
         if (ret)
                 return ret;
 
         if (iocb->ki_flags & IOCB_DIRECT) {
                 ret = generic_file_direct_write(iocb, from);
                 /*
                  * If the write stopped short of completing, fall back to
                  * buffered writes.  Some filesystems do this for writes to
                  * holes, for example.  For DAX files, a buffered write will
                  * not succeed (even if it did, DAX does not handle dirty
                  * page-cache pages correctly).
                  */
                 if (ret < 0 || !iov_iter_count(from) || IS_DAX(inode))
                         return ret;
                 return direct_write_fallback(iocb, from, ret,
                                 generic_perform_write(iocb, from));
         }
 
         return generic_perform_write(iocb, from);
 }
 EXPORT_SYMBOL(__generic_file_write_iter);
 
 /**
  * generic_file_write_iter - write data to a file
  * @iocb:       IO state structure
  * @from:       iov_iter with data to write
  *
  * This is a wrapper around __generic_file_write_iter() to be used by most
  * filesystems. It takes care of syncing the file in case of O_SYNC file
  * and acquires i_rwsem as needed.
  * Return:
  * * negative error code if no data has been written at all of
  *   vfs_fsync_range() failed for a synchronous write
  * * number of bytes written, even for truncated writes
  */
 ssize_t generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 {
         struct file *file = iocb->ki_filp;
         struct inode *inode = file->f_mapping->host;
         ssize_t ret;
 
         inode_lock(inode);
         ret = generic_write_checks(iocb, from);
         if (ret > 0)
                 ret = __generic_file_write_iter(iocb, from);
         inode_unlock(inode);
 
         if (ret > 0)
                 ret = generic_write_sync(iocb, ret);
         return ret;
 }
 EXPORT_SYMBOL(generic_file_write_iter);
 
 /**
  * filemap_release_folio() - Release fs-specific metadata on a folio.
  * @folio: The folio which the kernel is trying to free.
  * @gfp: Memory allocation flags (and I/O mode).
  *
  * The address_space is trying to release any data attached to a folio
  * (presumably at folio->private).
  *
  * This will also be called if the private_2 flag is set on a page,
  * indicating that the folio has other metadata associated with it.
  *
  * The @gfp argument specifies whether I/O may be performed to release
  * this page (__GFP_IO), and whether the call may block
  * (__GFP_RECLAIM & __GFP_FS).
  *
  * Return: %true if the release was successful, otherwise %false.
  */
 bool filemap_release_folio(struct folio *folio, gfp_t gfp)
 {
         struct address_space * const mapping = folio->mapping;
 
         BUG_ON(!folio_test_locked(folio));
         if (!folio_needs_release(folio))
                 return true;
         if (folio_test_writeback(folio))
                 return false;
 
         if (mapping && mapping->a_ops->release_folio)
                 return mapping->a_ops->release_folio(folio, gfp);
         return try_to_free_buffers(folio);
 }
 EXPORT_SYMBOL(filemap_release_folio);
 
 /**
  * filemap_invalidate_inode - Invalidate/forcibly write back a range of an inode's pagecache
  * @inode: The inode to flush
  * @flush: Set to write back rather than simply invalidate.
  * @start: First byte to in range.
  * @end: Last byte in range (inclusive), or LLONG_MAX for everything from start
  *       onwards.
  *
  * Invalidate all the folios on an inode that contribute to the specified
  * range, possibly writing them back first.  Whilst the operation is
  * undertaken, the invalidate lock is held to prevent new folios from being
  * installed.
  */
 int filemap_invalidate_inode(struct inode *inode, bool flush,
                              loff_t start, loff_t end)
 {
         struct address_space *mapping = inode->i_mapping;
         pgoff_t first = start >> PAGE_SHIFT;
         pgoff_t last = end >> PAGE_SHIFT;
         pgoff_t nr = end == LLONG_MAX ? ULONG_MAX : last - first + 1;
 
         if (!mapping || !mapping->nrpages || end < start)
                 goto out;
 
         /* Prevent new folios from being added to the inode. */
         filemap_invalidate_lock(mapping);
 
         if (!mapping->nrpages)
                 goto unlock;
 
         unmap_mapping_pages(mapping, first, nr, false);
 
         /* Write back the data if we're asked to. */
         if (flush) {
                 struct writeback_control wbc = {
                         .sync_mode      = WB_SYNC_ALL,
                         .nr_to_write    = LONG_MAX,
                         .range_start    = start,
                         .range_end      = end,
                 };
 
                 filemap_fdatawrite_wbc(mapping, &wbc);
         }
 
         /* Wait for writeback to complete on all folios and discard. */
         invalidate_inode_pages2_range(mapping, start / PAGE_SIZE, end / PAGE_SIZE);
 
 unlock:
         filemap_invalidate_unlock(mapping);
 out:
         return filemap_check_errors(mapping);
 }
 EXPORT_SYMBOL_GPL(filemap_invalidate_inode);
 
 #ifdef CONFIG_CACHESTAT_SYSCALL
 /**
  * filemap_cachestat() - compute the page cache statistics of a mapping
  * @mapping:    The mapping to compute the statistics for.
  * @first_index:        The starting page cache index.
  * @last_index: The final page index (inclusive).
  * @cs: the cachestat struct to write the result to.
  *
  * This will query the page cache statistics of a mapping in the
  * page range of [first_index, last_index] (inclusive). The statistics
  * queried include: number of dirty pages, number of pages marked for
  * writeback, and the number of (recently) evicted pages.
  */
 static void filemap_cachestat(struct address_space *mapping,
                 pgoff_t first_index, pgoff_t last_index, struct cachestat *cs)
 {
         XA_STATE(xas, &mapping->i_pages, first_index);
         struct folio *folio;
 
         /* Flush stats (and potentially sleep) outside the RCU read section. */
         mem_cgroup_flush_stats_ratelimited(NULL);
 
         rcu_read_lock();
         xas_for_each(&xas, folio, last_index) {
                 int order;
                 unsigned long nr_pages;
                 pgoff_t folio_first_index, folio_last_index;
 
                 /*
                  * Don't deref the folio. It is not pinned, and might
                  * get freed (and reused) underneath us.
                  *
                  * We *could* pin it, but that would be expensive for
                  * what should be a fast and lightweight syscall.
                  *
                  * Instead, derive all information of interest from
                  * the rcu-protected xarray.
                  */
 
                 if (xas_retry(&xas, folio))
                         continue;
 
                 order = xa_get_order(xas.xa, xas.xa_index);
                 nr_pages = 1 << order;
                 folio_first_index = round_down(xas.xa_index, 1 << order);
                 folio_last_index = folio_first_index + nr_pages - 1;
 
                 /* Folios might straddle the range boundaries, only count covered pages */
                 if (folio_first_index < first_index)
                         nr_pages -= first_index - folio_first_index;
 
                 if (folio_last_index > last_index)
                         nr_pages -= folio_last_index - last_index;
 
                 if (xa_is_value(folio)) {
                         /* page is evicted */
                         void *shadow = (void *)folio;
                         bool workingset; /* not used */
 
                         cs->nr_evicted += nr_pages;
 
 #ifdef CONFIG_SWAP /* implies CONFIG_MMU */
                         if (shmem_mapping(mapping)) {
                                 /* shmem file - in swap cache */
                                 swp_entry_t swp = radix_to_swp_entry(folio);
 
                                 /* swapin error results in poisoned entry */
                                 if (non_swap_entry(swp))
                                         goto resched;
 
                                 /*
                                  * Getting a swap entry from the shmem
                                  * inode means we beat
                                  * shmem_unuse(). rcu_read_lock()
                                  * ensures swapoff waits for us before
                                  * freeing the swapper space. However,
                                  * we can race with swapping and
                                  * invalidation, so there might not be
                                  * a shadow in the swapcache (yet).
                                  */
                                 shadow = get_shadow_from_swap_cache(swp);
                                 if (!shadow)
                                         goto resched;
                         }
 #endif
                         if (workingset_test_recent(shadow, true, &workingset, false))
                                 cs->nr_recently_evicted += nr_pages;
 
                         goto resched;
                 }
 
                 /* page is in cache */
                 cs->nr_cache += nr_pages;
 
                 if (xas_get_mark(&xas, PAGECACHE_TAG_DIRTY))
                         cs->nr_dirty += nr_pages;
 
                 if (xas_get_mark(&xas, PAGECACHE_TAG_WRITEBACK))
                         cs->nr_writeback += nr_pages;
 
 resched:
                 if (need_resched()) {
                         xas_pause(&xas);
                         cond_resched_rcu();
                 }
         }
         rcu_read_unlock();
 }
 
 /*
  * The cachestat(2) system call.
  *
  * cachestat() returns the page cache statistics of a file in the
  * bytes range specified by `off` and `len`: number of cached pages,
  * number of dirty pages, number of pages marked for writeback,
  * number of evicted pages, and number of recently evicted pages.
  *
  * An evicted page is a page that is previously in the page cache
  * but has been evicted since. A page is recently evicted if its last
  * eviction was recent enough that its reentry to the cache would
  * indicate that it is actively being used by the system, and that
  * there is memory pressure on the system.
  *
  * `off` and `len` must be non-negative integers. If `len` > 0,
  * the queried range is [`off`, `off` + `len`]. If `len` == 0,
  * we will query in the range from `off` to the end of the file.
  *
  * The `flags` argument is unused for now, but is included for future
  * extensibility. User should pass 0 (i.e no flag specified).
  *
  * Currently, hugetlbfs is not supported.
  *
  * Because the status of a page can change after cachestat() checks it
  * but before it returns to the application, the returned values may
  * contain stale information.
  *
  * return values:
  *  zero        - success
  *  -EFAULT     - cstat or cstat_range points to an illegal address
  *  -EINVAL     - invalid flags
  *  -EBADF      - invalid file descriptor
  *  -EOPNOTSUPP - file descriptor is of a hugetlbfs file
  */
 SYSCALL_DEFINE4(cachestat, unsigned int, fd,
                 struct cachestat_range __user *, cstat_range,
                 struct cachestat __user *, cstat, unsigned int, flags)
 {
         struct fd f = fdget(fd);
         struct address_space *mapping;
         struct cachestat_range csr;
         struct cachestat cs;
         pgoff_t first_index, last_index;
 
         if (!f.file)
                 return -EBADF;
 
         if (copy_from_user(&csr, cstat_range,
                         sizeof(struct cachestat_range))) {
                 fdput(f);
                 return -EFAULT;
         }
 
         /* hugetlbfs is not supported */
         if (is_file_hugepages(f.file)) {
                 fdput(f);
                 return -EOPNOTSUPP;
         }
 
         if (flags != 0) {
                 fdput(f);
                 return -EINVAL;
         }
 
         first_index = csr.off >> PAGE_SHIFT;
         last_index =
                 csr.len == 0 ? ULONG_MAX : (csr.off + csr.len - 1) >> PAGE_SHIFT;
         memset(&cs, 0, sizeof(struct cachestat));
         mapping = f.file->f_mapping;
         filemap_cachestat(mapping, first_index, last_index, &cs);
         fdput(f);
 
         if (copy_to_user(cstat, &cs, sizeof(struct cachestat)))
                 return -EFAULT;
 
         return 0;
 }
 #endif /* CONFIG_CACHESTAT_SYSCALL */