TOMOYO Linux Cross Reference
Linux/kernel/printk/printk.c

   // SPDX-License-Identifier: GPL-2.0-only
   /*
    *  linux/kernel/printk.c
    *
    *  Copyright (C) 1991, 1992  Linus Torvalds
    *
    * Modified to make sys_syslog() more flexible: added commands to
    * return the last 4k of kernel messages, regardless of whether
    * they've been read or not.  Added option to suppress kernel printk's
   * to the console.  Added hook for sending the console messages
   * elsewhere, in preparation for a serial line console (someday).
   * Ted Ts'o, 2/11/93.
   * Modified for sysctl support, 1/8/97, Chris Horn.
   * Fixed SMP synchronization, 08/08/99, Manfred Spraul
   *     manfred@colorfullife.com
   * Rewrote bits to get rid of console_lock
   *      01Mar01 Andrew Morton
   */
  
  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  
  #include <linux/kernel.h>
  #include <linux/mm.h>
  #include <linux/tty.h>
  #include <linux/tty_driver.h>
  #include <linux/console.h>
  #include <linux/init.h>
  #include <linux/jiffies.h>
  #include <linux/nmi.h>
  #include <linux/module.h>
  #include <linux/moduleparam.h>
  #include <linux/delay.h>
  #include <linux/smp.h>
  #include <linux/security.h>
  #include <linux/memblock.h>
  #include <linux/syscalls.h>
  #include <linux/vmcore_info.h>
  #include <linux/ratelimit.h>
  #include <linux/kmsg_dump.h>
  #include <linux/syslog.h>
  #include <linux/cpu.h>
  #include <linux/rculist.h>
  #include <linux/poll.h>
  #include <linux/irq_work.h>
  #include <linux/ctype.h>
  #include <linux/uio.h>
  #include <linux/sched/clock.h>
  #include <linux/sched/debug.h>
  #include <linux/sched/task_stack.h>
  
  #include <linux/uaccess.h>
  #include <asm/sections.h>
  
  #include <trace/events/initcall.h>
  #define CREATE_TRACE_POINTS
  #include <trace/events/printk.h>
  
  #include "printk_ringbuffer.h"
  #include "console_cmdline.h"
  #include "braille.h"
  #include "internal.h"
  
  int console_printk[4] = {
          CONSOLE_LOGLEVEL_DEFAULT,       /* console_loglevel */
          MESSAGE_LOGLEVEL_DEFAULT,       /* default_message_loglevel */
          CONSOLE_LOGLEVEL_MIN,           /* minimum_console_loglevel */
          CONSOLE_LOGLEVEL_DEFAULT,       /* default_console_loglevel */
  };
  EXPORT_SYMBOL_GPL(console_printk);
  
  atomic_t ignore_console_lock_warning __read_mostly = ATOMIC_INIT(0);
  EXPORT_SYMBOL(ignore_console_lock_warning);
  
  EXPORT_TRACEPOINT_SYMBOL_GPL(console);
  
  /*
   * Low level drivers may need that to know if they can schedule in
   * their unblank() callback or not. So let's export it.
   */
  int oops_in_progress;
  EXPORT_SYMBOL(oops_in_progress);
  
  /*
   * console_mutex protects console_list updates and console->flags updates.
   * The flags are synchronized only for consoles that are registered, i.e.
   * accessible via the console list.
   */
  static DEFINE_MUTEX(console_mutex);
  
  /*
   * console_sem protects updates to console->seq
   * and also provides serialization for console printing.
   */
  static DEFINE_SEMAPHORE(console_sem, 1);
  HLIST_HEAD(console_list);
  EXPORT_SYMBOL_GPL(console_list);
  DEFINE_STATIC_SRCU(console_srcu);
  
  /*
  * System may need to suppress printk message under certain
  * circumstances, like after kernel panic happens.
  */
 int __read_mostly suppress_printk;
 
 #ifdef CONFIG_LOCKDEP
 static struct lockdep_map console_lock_dep_map = {
         .name = "console_lock"
 };
 
 void lockdep_assert_console_list_lock_held(void)
 {
         lockdep_assert_held(&console_mutex);
 }
 EXPORT_SYMBOL(lockdep_assert_console_list_lock_held);
 #endif
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 bool console_srcu_read_lock_is_held(void)
 {
         return srcu_read_lock_held(&console_srcu);
 }
 EXPORT_SYMBOL(console_srcu_read_lock_is_held);
 #endif
 
 enum devkmsg_log_bits {
         __DEVKMSG_LOG_BIT_ON = 0,
         __DEVKMSG_LOG_BIT_OFF,
         __DEVKMSG_LOG_BIT_LOCK,
 };
 
 enum devkmsg_log_masks {
         DEVKMSG_LOG_MASK_ON             = BIT(__DEVKMSG_LOG_BIT_ON),
         DEVKMSG_LOG_MASK_OFF            = BIT(__DEVKMSG_LOG_BIT_OFF),
         DEVKMSG_LOG_MASK_LOCK           = BIT(__DEVKMSG_LOG_BIT_LOCK),
 };
 
 /* Keep both the 'on' and 'off' bits clear, i.e. ratelimit by default: */
 #define DEVKMSG_LOG_MASK_DEFAULT        0
 
 static unsigned int __read_mostly devkmsg_log = DEVKMSG_LOG_MASK_DEFAULT;
 
 static int __control_devkmsg(char *str)
 {
         size_t len;
 
         if (!str)
                 return -EINVAL;
 
         len = str_has_prefix(str, "on");
         if (len) {
                 devkmsg_log = DEVKMSG_LOG_MASK_ON;
                 return len;
         }
 
         len = str_has_prefix(str, "off");
         if (len) {
                 devkmsg_log = DEVKMSG_LOG_MASK_OFF;
                 return len;
         }
 
         len = str_has_prefix(str, "ratelimit");
         if (len) {
                 devkmsg_log = DEVKMSG_LOG_MASK_DEFAULT;
                 return len;
         }
 
         return -EINVAL;
 }
 
 static int __init control_devkmsg(char *str)
 {
         if (__control_devkmsg(str) < 0) {
                 pr_warn("printk.devkmsg: bad option string '%s'\n", str);
                 return 1;
         }
 
         /*
          * Set sysctl string accordingly:
          */
         if (devkmsg_log == DEVKMSG_LOG_MASK_ON)
                 strscpy(devkmsg_log_str, "on");
         else if (devkmsg_log == DEVKMSG_LOG_MASK_OFF)
                 strscpy(devkmsg_log_str, "off");
         /* else "ratelimit" which is set by default. */
 
         /*
          * Sysctl cannot change it anymore. The kernel command line setting of
          * this parameter is to force the setting to be permanent throughout the
          * runtime of the system. This is a precation measure against userspace
          * trying to be a smarta** and attempting to change it up on us.
          */
         devkmsg_log |= DEVKMSG_LOG_MASK_LOCK;
 
         return 1;
 }
 __setup("printk.devkmsg=", control_devkmsg);
 
 char devkmsg_log_str[DEVKMSG_STR_MAX_SIZE] = "ratelimit";
 #if defined(CONFIG_PRINTK) && defined(CONFIG_SYSCTL)
 int devkmsg_sysctl_set_loglvl(const struct ctl_table *table, int write,
                               void *buffer, size_t *lenp, loff_t *ppos)
 {
         char old_str[DEVKMSG_STR_MAX_SIZE];
         unsigned int old;
         int err;
 
         if (write) {
                 if (devkmsg_log & DEVKMSG_LOG_MASK_LOCK)
                         return -EINVAL;
 
                 old = devkmsg_log;
                 strscpy(old_str, devkmsg_log_str);
         }
 
         err = proc_dostring(table, write, buffer, lenp, ppos);
         if (err)
                 return err;
 
         if (write) {
                 err = __control_devkmsg(devkmsg_log_str);
 
                 /*
                  * Do not accept an unknown string OR a known string with
                  * trailing crap...
                  */
                 if (err < 0 || (err + 1 != *lenp)) {
 
                         /* ... and restore old setting. */
                         devkmsg_log = old;
                         strscpy(devkmsg_log_str, old_str);
 
                         return -EINVAL;
                 }
         }
 
         return 0;
 }
 #endif /* CONFIG_PRINTK && CONFIG_SYSCTL */
 
 /**
  * console_list_lock - Lock the console list
  *
  * For console list or console->flags updates
  */
 void console_list_lock(void)
 {
         /*
          * In unregister_console() and console_force_preferred_locked(),
          * synchronize_srcu() is called with the console_list_lock held.
          * Therefore it is not allowed that the console_list_lock is taken
          * with the srcu_lock held.
          *
          * Detecting if this context is really in the read-side critical
          * section is only possible if the appropriate debug options are
          * enabled.
          */
         WARN_ON_ONCE(debug_lockdep_rcu_enabled() &&
                      srcu_read_lock_held(&console_srcu));
 
         mutex_lock(&console_mutex);
 }
 EXPORT_SYMBOL(console_list_lock);
 
 /**
  * console_list_unlock - Unlock the console list
  *
  * Counterpart to console_list_lock()
  */
 void console_list_unlock(void)
 {
         mutex_unlock(&console_mutex);
 }
 EXPORT_SYMBOL(console_list_unlock);
 
 /**
  * console_srcu_read_lock - Register a new reader for the
  *      SRCU-protected console list
  *
  * Use for_each_console_srcu() to iterate the console list
  *
  * Context: Any context.
  * Return: A cookie to pass to console_srcu_read_unlock().
  */
 int console_srcu_read_lock(void)
 {
         return srcu_read_lock_nmisafe(&console_srcu);
 }
 EXPORT_SYMBOL(console_srcu_read_lock);
 
 /**
  * console_srcu_read_unlock - Unregister an old reader from
  *      the SRCU-protected console list
  * @cookie: cookie returned from console_srcu_read_lock()
  *
  * Counterpart to console_srcu_read_lock()
  */
 void console_srcu_read_unlock(int cookie)
 {
         srcu_read_unlock_nmisafe(&console_srcu, cookie);
 }
 EXPORT_SYMBOL(console_srcu_read_unlock);
 
 /*
  * Helper macros to handle lockdep when locking/unlocking console_sem. We use
  * macros instead of functions so that _RET_IP_ contains useful information.
  */
 #define down_console_sem() do { \
         down(&console_sem);\
         mutex_acquire(&console_lock_dep_map, 0, 0, _RET_IP_);\
 } while (0)
 
 static int __down_trylock_console_sem(unsigned long ip)
 {
         int lock_failed;
         unsigned long flags;
 
         /*
          * Here and in __up_console_sem() we need to be in safe mode,
          * because spindump/WARN/etc from under console ->lock will
          * deadlock in printk()->down_trylock_console_sem() otherwise.
          */
         printk_safe_enter_irqsave(flags);
         lock_failed = down_trylock(&console_sem);
         printk_safe_exit_irqrestore(flags);
 
         if (lock_failed)
                 return 1;
         mutex_acquire(&console_lock_dep_map, 0, 1, ip);
         return 0;
 }
 #define down_trylock_console_sem() __down_trylock_console_sem(_RET_IP_)
 
 static void __up_console_sem(unsigned long ip)
 {
         unsigned long flags;
 
         mutex_release(&console_lock_dep_map, ip);
 
         printk_safe_enter_irqsave(flags);
         up(&console_sem);
         printk_safe_exit_irqrestore(flags);
 }
 #define up_console_sem() __up_console_sem(_RET_IP_)
 
 static bool panic_in_progress(void)
 {
         return unlikely(atomic_read(&panic_cpu) != PANIC_CPU_INVALID);
 }
 
 /* Return true if a panic is in progress on the current CPU. */
 bool this_cpu_in_panic(void)
 {
         /*
          * We can use raw_smp_processor_id() here because it is impossible for
          * the task to be migrated to the panic_cpu, or away from it. If
          * panic_cpu has already been set, and we're not currently executing on
          * that CPU, then we never will be.
          */
         return unlikely(atomic_read(&panic_cpu) == raw_smp_processor_id());
 }
 
 /*
  * Return true if a panic is in progress on a remote CPU.
  *
  * On true, the local CPU should immediately release any printing resources
  * that may be needed by the panic CPU.
  */
 bool other_cpu_in_panic(void)
 {
         return (panic_in_progress() && !this_cpu_in_panic());
 }
 
 /*
  * This is used for debugging the mess that is the VT code by
  * keeping track if we have the console semaphore held. It's
  * definitely not the perfect debug tool (we don't know if _WE_
  * hold it and are racing, but it helps tracking those weird code
  * paths in the console code where we end up in places I want
  * locked without the console semaphore held).
  */
 static int console_locked;
 
 /*
  *      Array of consoles built from command line options (console=)
  */
 
 #define MAX_CMDLINECONSOLES 8
 
 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
 
 static int preferred_console = -1;
 int console_set_on_cmdline;
 EXPORT_SYMBOL(console_set_on_cmdline);
 
 /* Flag: console code may call schedule() */
 static int console_may_schedule;
 
 enum con_msg_format_flags {
         MSG_FORMAT_DEFAULT      = 0,
         MSG_FORMAT_SYSLOG       = (1 << 0),
 };
 
 static int console_msg_format = MSG_FORMAT_DEFAULT;
 
 /*
  * The printk log buffer consists of a sequenced collection of records, each
  * containing variable length message text. Every record also contains its
  * own meta-data (@info).
  *
  * Every record meta-data carries the timestamp in microseconds, as well as
  * the standard userspace syslog level and syslog facility. The usual kernel
  * messages use LOG_KERN; userspace-injected messages always carry a matching
  * syslog facility, by default LOG_USER. The origin of every message can be
  * reliably determined that way.
  *
  * The human readable log message of a record is available in @text, the
  * length of the message text in @text_len. The stored message is not
  * terminated.
  *
  * Optionally, a record can carry a dictionary of properties (key/value
  * pairs), to provide userspace with a machine-readable message context.
  *
  * Examples for well-defined, commonly used property names are:
  *   DEVICE=b12:8               device identifier
  *                                b12:8         block dev_t
  *                                c127:3        char dev_t
  *                                n8            netdev ifindex
  *                                +sound:card0  subsystem:devname
  *   SUBSYSTEM=pci              driver-core subsystem name
  *
  * Valid characters in property names are [a-zA-Z0-9.-_]. Property names
  * and values are terminated by a '\0' character.
  *
  * Example of record values:
  *   record.text_buf                = "it's a line" (unterminated)
  *   record.info.seq                = 56
  *   record.info.ts_nsec            = 36863
  *   record.info.text_len           = 11
  *   record.info.facility           = 0 (LOG_KERN)
  *   record.info.flags              = 0
  *   record.info.level              = 3 (LOG_ERR)
  *   record.info.caller_id          = 299 (task 299)
  *   record.info.dev_info.subsystem = "pci" (terminated)
  *   record.info.dev_info.device    = "+pci:0000:00:01.0" (terminated)
  *
  * The 'struct printk_info' buffer must never be directly exported to
  * userspace, it is a kernel-private implementation detail that might
  * need to be changed in the future, when the requirements change.
  *
  * /dev/kmsg exports the structured data in the following line format:
  *   "<level>,<sequnum>,<timestamp>,<contflag>[,additional_values, ... ];<message text>\n"
  *
  * Users of the export format should ignore possible additional values
  * separated by ',', and find the message after the ';' character.
  *
  * The optional key/value pairs are attached as continuation lines starting
  * with a space character and terminated by a newline. All possible
  * non-prinatable characters are escaped in the "\xff" notation.
  */
 
 /* syslog_lock protects syslog_* variables and write access to clear_seq. */
 static DEFINE_MUTEX(syslog_lock);
 
 #ifdef CONFIG_PRINTK
 DECLARE_WAIT_QUEUE_HEAD(log_wait);
 /* All 3 protected by @syslog_lock. */
 /* the next printk record to read by syslog(READ) or /proc/kmsg */
 static u64 syslog_seq;
 static size_t syslog_partial;
 static bool syslog_time;
 
 struct latched_seq {
         seqcount_latch_t        latch;
         u64                     val[2];
 };
 
 /*
  * The next printk record to read after the last 'clear' command. There are
  * two copies (updated with seqcount_latch) so that reads can locklessly
  * access a valid value. Writers are synchronized by @syslog_lock.
  */
 static struct latched_seq clear_seq = {
         .latch          = SEQCNT_LATCH_ZERO(clear_seq.latch),
         .val[0]         = 0,
         .val[1]         = 0,
 };
 
 #define LOG_LEVEL(v)            ((v) & 0x07)
 #define LOG_FACILITY(v)         ((v) >> 3 & 0xff)
 
 /* record buffer */
 #define LOG_ALIGN __alignof__(unsigned long)
 #define __LOG_BUF_LEN (1 << CONFIG_LOG_BUF_SHIFT)
 #define LOG_BUF_LEN_MAX (u32)(1 << 31)
 static char __log_buf[__LOG_BUF_LEN] __aligned(LOG_ALIGN);
 static char *log_buf = __log_buf;
 static u32 log_buf_len = __LOG_BUF_LEN;
 
 /*
  * Define the average message size. This only affects the number of
  * descriptors that will be available. Underestimating is better than
  * overestimating (too many available descriptors is better than not enough).
  */
 #define PRB_AVGBITS 5   /* 32 character average length */
 
 #if CONFIG_LOG_BUF_SHIFT <= PRB_AVGBITS
 #error CONFIG_LOG_BUF_SHIFT value too small.
 #endif
 _DEFINE_PRINTKRB(printk_rb_static, CONFIG_LOG_BUF_SHIFT - PRB_AVGBITS,
                  PRB_AVGBITS, &__log_buf[0]);
 
 static struct printk_ringbuffer printk_rb_dynamic;
 
 struct printk_ringbuffer *prb = &printk_rb_static;
 
 /*
  * We cannot access per-CPU data (e.g. per-CPU flush irq_work) before
  * per_cpu_areas are initialised. This variable is set to true when
  * it's safe to access per-CPU data.
  */
 static bool __printk_percpu_data_ready __ro_after_init;
 
 bool printk_percpu_data_ready(void)
 {
         return __printk_percpu_data_ready;
 }
 
 /* Must be called under syslog_lock. */
 static void latched_seq_write(struct latched_seq *ls, u64 val)
 {
         raw_write_seqcount_latch(&ls->latch);
         ls->val[0] = val;
         raw_write_seqcount_latch(&ls->latch);
         ls->val[1] = val;
 }
 
 /* Can be called from any context. */
 static u64 latched_seq_read_nolock(struct latched_seq *ls)
 {
         unsigned int seq;
         unsigned int idx;
         u64 val;
 
         do {
                 seq = raw_read_seqcount_latch(&ls->latch);
                 idx = seq & 0x1;
                 val = ls->val[idx];
         } while (raw_read_seqcount_latch_retry(&ls->latch, seq));
 
         return val;
 }
 
 /* Return log buffer address */
 char *log_buf_addr_get(void)
 {
         return log_buf;
 }
 
 /* Return log buffer size */
 u32 log_buf_len_get(void)
 {
         return log_buf_len;
 }
 
 /*
  * Define how much of the log buffer we could take at maximum. The value
  * must be greater than two. Note that only half of the buffer is available
  * when the index points to the middle.
  */
 #define MAX_LOG_TAKE_PART 4
 static const char trunc_msg[] = "<truncated>";
 
 static void truncate_msg(u16 *text_len, u16 *trunc_msg_len)
 {
         /*
          * The message should not take the whole buffer. Otherwise, it might
          * get removed too soon.
          */
         u32 max_text_len = log_buf_len / MAX_LOG_TAKE_PART;
 
         if (*text_len > max_text_len)
                 *text_len = max_text_len;
 
         /* enable the warning message (if there is room) */
         *trunc_msg_len = strlen(trunc_msg);
         if (*text_len >= *trunc_msg_len)
                 *text_len -= *trunc_msg_len;
         else
                 *trunc_msg_len = 0;
 }
 
 int dmesg_restrict = IS_ENABLED(CONFIG_SECURITY_DMESG_RESTRICT);
 
 static int syslog_action_restricted(int type)
 {
         if (dmesg_restrict)
                 return 1;
         /*
          * Unless restricted, we allow "read all" and "get buffer size"
          * for everybody.
          */
         return type != SYSLOG_ACTION_READ_ALL &&
                type != SYSLOG_ACTION_SIZE_BUFFER;
 }
 
 static int check_syslog_permissions(int type, int source)
 {
         /*
          * If this is from /proc/kmsg and we've already opened it, then we've
          * already done the capabilities checks at open time.
          */
         if (source == SYSLOG_FROM_PROC && type != SYSLOG_ACTION_OPEN)
                 goto ok;
 
         if (syslog_action_restricted(type)) {
                 if (capable(CAP_SYSLOG))
                         goto ok;
                 return -EPERM;
         }
 ok:
         return security_syslog(type);
 }
 
 static void append_char(char **pp, char *e, char c)
 {
         if (*pp < e)
                 *(*pp)++ = c;
 }
 
 static ssize_t info_print_ext_header(char *buf, size_t size,
                                      struct printk_info *info)
 {
         u64 ts_usec = info->ts_nsec;
         char caller[20];
 #ifdef CONFIG_PRINTK_CALLER
         u32 id = info->caller_id;
 
         snprintf(caller, sizeof(caller), ",caller=%c%u",
                  id & 0x80000000 ? 'C' : 'T', id & ~0x80000000);
 #else
         caller[0] = '\0';
 #endif
 
         do_div(ts_usec, 1000);
 
         return scnprintf(buf, size, "%u,%llu,%llu,%c%s;",
                          (info->facility << 3) | info->level, info->seq,
                          ts_usec, info->flags & LOG_CONT ? 'c' : '-', caller);
 }
 
 static ssize_t msg_add_ext_text(char *buf, size_t size,
                                 const char *text, size_t text_len,
                                 unsigned char endc)
 {
         char *p = buf, *e = buf + size;
         size_t i;
 
         /* escape non-printable characters */
         for (i = 0; i < text_len; i++) {
                 unsigned char c = text[i];
 
                 if (c < ' ' || c >= 127 || c == '\\')
                         p += scnprintf(p, e - p, "\\x%02x", c);
                 else
                         append_char(&p, e, c);
         }
         append_char(&p, e, endc);
 
         return p - buf;
 }
 
 static ssize_t msg_add_dict_text(char *buf, size_t size,
                                  const char *key, const char *val)
 {
         size_t val_len = strlen(val);
         ssize_t len;
 
         if (!val_len)
                 return 0;
 
         len = msg_add_ext_text(buf, size, "", 0, ' ');  /* dict prefix */
         len += msg_add_ext_text(buf + len, size - len, key, strlen(key), '=');
         len += msg_add_ext_text(buf + len, size - len, val, val_len, '\n');
 
         return len;
 }
 
 static ssize_t msg_print_ext_body(char *buf, size_t size,
                                   char *text, size_t text_len,
                                   struct dev_printk_info *dev_info)
 {
         ssize_t len;
 
         len = msg_add_ext_text(buf, size, text, text_len, '\n');
 
         if (!dev_info)
                 goto out;
 
         len += msg_add_dict_text(buf + len, size - len, "SUBSYSTEM",
                                  dev_info->subsystem);
         len += msg_add_dict_text(buf + len, size - len, "DEVICE",
                                  dev_info->device);
 out:
         return len;
 }
 
 /* /dev/kmsg - userspace message inject/listen interface */
 struct devkmsg_user {
         atomic64_t seq;
         struct ratelimit_state rs;
         struct mutex lock;
         struct printk_buffers pbufs;
 };
 
 static __printf(3, 4) __cold
 int devkmsg_emit(int facility, int level, const char *fmt, ...)
 {
         va_list args;
         int r;
 
         va_start(args, fmt);
         r = vprintk_emit(facility, level, NULL, fmt, args);
         va_end(args);
 
         return r;
 }
 
 static ssize_t devkmsg_write(struct kiocb *iocb, struct iov_iter *from)
 {
         char *buf, *line;
         int level = default_message_loglevel;
         int facility = 1;       /* LOG_USER */
         struct file *file = iocb->ki_filp;
         struct devkmsg_user *user = file->private_data;
         size_t len = iov_iter_count(from);
         ssize_t ret = len;
 
         if (len > PRINTKRB_RECORD_MAX)
                 return -EINVAL;
 
         /* Ignore when user logging is disabled. */
         if (devkmsg_log & DEVKMSG_LOG_MASK_OFF)
                 return len;
 
         /* Ratelimit when not explicitly enabled. */
         if (!(devkmsg_log & DEVKMSG_LOG_MASK_ON)) {
                 if (!___ratelimit(&user->rs, current->comm))
                         return ret;
         }
 
         buf = kmalloc(len+1, GFP_KERNEL);
         if (buf == NULL)
                 return -ENOMEM;
 
         buf[len] = '\0';
         if (!copy_from_iter_full(buf, len, from)) {
                 kfree(buf);
                 return -EFAULT;
         }
 
         /*
          * Extract and skip the syslog prefix <[0-9]*>. Coming from userspace
          * the decimal value represents 32bit, the lower 3 bit are the log
          * level, the rest are the log facility.
          *
          * If no prefix or no userspace facility is specified, we
          * enforce LOG_USER, to be able to reliably distinguish
          * kernel-generated messages from userspace-injected ones.
          */
         line = buf;
         if (line[0] == '<') {
                 char *endp = NULL;
                 unsigned int u;
 
                 u = simple_strtoul(line + 1, &endp, 10);
                 if (endp && endp[0] == '>') {
                         level = LOG_LEVEL(u);
                         if (LOG_FACILITY(u) != 0)
                                 facility = LOG_FACILITY(u);
                         endp++;
                         line = endp;
                 }
         }
 
         devkmsg_emit(facility, level, "%s", line);
         kfree(buf);
         return ret;
 }
 
 static ssize_t devkmsg_read(struct file *file, char __user *buf,
                             size_t count, loff_t *ppos)
 {
         struct devkmsg_user *user = file->private_data;
         char *outbuf = &user->pbufs.outbuf[0];
         struct printk_message pmsg = {
                 .pbufs = &user->pbufs,
         };
         ssize_t ret;
 
         ret = mutex_lock_interruptible(&user->lock);
         if (ret)
                 return ret;
 
         if (!printk_get_next_message(&pmsg, atomic64_read(&user->seq), true, false)) {
                 if (file->f_flags & O_NONBLOCK) {
                         ret = -EAGAIN;
                         goto out;
                 }
 
                 /*
                  * Guarantee this task is visible on the waitqueue before
                  * checking the wake condition.
                  *
                  * The full memory barrier within set_current_state() of
                  * prepare_to_wait_event() pairs with the full memory barrier
                  * within wq_has_sleeper().
                  *
                  * This pairs with __wake_up_klogd:A.
                  */
                 ret = wait_event_interruptible(log_wait,
                                 printk_get_next_message(&pmsg, atomic64_read(&user->seq), true,
                                                         false)); /* LMM(devkmsg_read:A) */
                 if (ret)
                         goto out;
         }
 
         if (pmsg.dropped) {
                 /* our last seen message is gone, return error and reset */
                 atomic64_set(&user->seq, pmsg.seq);
                 ret = -EPIPE;
                 goto out;
         }
 
         atomic64_set(&user->seq, pmsg.seq + 1);
 
         if (pmsg.outbuf_len > count) {
                 ret = -EINVAL;
                 goto out;
         }
 
         if (copy_to_user(buf, outbuf, pmsg.outbuf_len)) {
                 ret = -EFAULT;
                 goto out;
         }
         ret = pmsg.outbuf_len;
 out:
         mutex_unlock(&user->lock);
         return ret;
 }
 
 /*
  * Be careful when modifying this function!!!
  *
  * Only few operations are supported because the device works only with the
  * entire variable length messages (records). Non-standard values are
  * returned in the other cases and has been this way for quite some time.
  * User space applications might depend on this behavior.
  */
 static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence)
 {
         struct devkmsg_user *user = file->private_data;
         loff_t ret = 0;
 
         if (offset)
                 return -ESPIPE;
 
         switch (whence) {
         case SEEK_SET:
                 /* the first record */
                 atomic64_set(&user->seq, prb_first_valid_seq(prb));
                 break;
         case SEEK_DATA:
                 /*
                  * The first record after the last SYSLOG_ACTION_CLEAR,
                  * like issued by 'dmesg -c'. Reading /dev/kmsg itself
                  * changes no global state, and does not clear anything.
                  */
                 atomic64_set(&user->seq, latched_seq_read_nolock(&clear_seq));
                 break;
         case SEEK_END:
                 /* after the last record */
                 atomic64_set(&user->seq, prb_next_seq(prb));
                 break;
         default:
                 ret = -EINVAL;
         }
         return ret;
 }
 
 static __poll_t devkmsg_poll(struct file *file, poll_table *wait)
 {
         struct devkmsg_user *user = file->private_data;
         struct printk_info info;
         __poll_t ret = 0;
 
         poll_wait(file, &log_wait, wait);
 
         if (prb_read_valid_info(prb, atomic64_read(&user->seq), &info, NULL)) {
                 /* return error when data has vanished underneath us */
                 if (info.seq != atomic64_read(&user->seq))
                         ret = EPOLLIN|EPOLLRDNORM|EPOLLERR|EPOLLPRI;
                 else
                         ret = EPOLLIN|EPOLLRDNORM;
         }
 
         return ret;
 }
 
 static int devkmsg_open(struct inode *inode, struct file *file)
 {
         struct devkmsg_user *user;
         int err;
 
         if (devkmsg_log & DEVKMSG_LOG_MASK_OFF)
                 return -EPERM;
 
         /* write-only does not need any file context */
         if ((file->f_flags & O_ACCMODE) != O_WRONLY) {
                 err = check_syslog_permissions(SYSLOG_ACTION_READ_ALL,
                                                SYSLOG_FROM_READER);
                 if (err)
                         return err;
         }
 
         user = kvmalloc(sizeof(struct devkmsg_user), GFP_KERNEL);
         if (!user)
                 return -ENOMEM;
 
         ratelimit_default_init(&user->rs);
         ratelimit_set_flags(&user->rs, RATELIMIT_MSG_ON_RELEASE);
 
         mutex_init(&user->lock);
 
         atomic64_set(&user->seq, prb_first_valid_seq(prb));
 
         file->private_data = user;
         return 0;
 }
 
 static int devkmsg_release(struct inode *inode, struct file *file)
 {
         struct devkmsg_user *user = file->private_data;
 
         ratelimit_state_exit(&user->rs);
 
         mutex_destroy(&user->lock);
         kvfree(user);
         return 0;
 }
 
 const struct file_operations kmsg_fops = {
         .open = devkmsg_open,
         .read = devkmsg_read,
         .write_iter = devkmsg_write,
         .llseek = devkmsg_llseek,
         .poll = devkmsg_poll,
         .release = devkmsg_release,
 };
 
 #ifdef CONFIG_VMCORE_INFO
 /*
  * This appends the listed symbols to /proc/vmcore
  *
  * /proc/vmcore is used by various utilities, like crash and makedumpfile to
  * obtain access to symbols that are otherwise very difficult to locate.  These
  * symbols are specifically used so that utilities can access and extract the
  * dmesg log from a vmcore file after a crash.
  */
 void log_buf_vmcoreinfo_setup(void)
 {
         struct dev_printk_info *dev_info = NULL;
 
         VMCOREINFO_SYMBOL(prb);
         VMCOREINFO_SYMBOL(printk_rb_static);
         VMCOREINFO_SYMBOL(clear_seq);
 
         /*
          * Export struct size and field offsets. User space tools can
          * parse it and detect any changes to structure down the line.
          */
 
         VMCOREINFO_STRUCT_SIZE(printk_ringbuffer);
         VMCOREINFO_OFFSET(printk_ringbuffer, desc_ring);
         VMCOREINFO_OFFSET(printk_ringbuffer, text_data_ring);
         VMCOREINFO_OFFSET(printk_ringbuffer, fail);
 
         VMCOREINFO_STRUCT_SIZE(prb_desc_ring);
         VMCOREINFO_OFFSET(prb_desc_ring, count_bits);
         VMCOREINFO_OFFSET(prb_desc_ring, descs);
         VMCOREINFO_OFFSET(prb_desc_ring, infos);
         VMCOREINFO_OFFSET(prb_desc_ring, head_id);
         VMCOREINFO_OFFSET(prb_desc_ring, tail_id);
 
         VMCOREINFO_STRUCT_SIZE(prb_desc);
         VMCOREINFO_OFFSET(prb_desc, state_var);
         VMCOREINFO_OFFSET(prb_desc, text_blk_lpos);
 
         VMCOREINFO_STRUCT_SIZE(prb_data_blk_lpos);
         VMCOREINFO_OFFSET(prb_data_blk_lpos, begin);
         VMCOREINFO_OFFSET(prb_data_blk_lpos, next);
 
         VMCOREINFO_STRUCT_SIZE(printk_info);
         VMCOREINFO_OFFSET(printk_info, seq);
         VMCOREINFO_OFFSET(printk_info, ts_nsec);
         VMCOREINFO_OFFSET(printk_info, text_len);
         VMCOREINFO_OFFSET(printk_info, caller_id);
         VMCOREINFO_OFFSET(printk_info, dev_info);
 
         VMCOREINFO_STRUCT_SIZE(dev_printk_info);
         VMCOREINFO_OFFSET(dev_printk_info, subsystem);
         VMCOREINFO_LENGTH(printk_info_subsystem, sizeof(dev_info->subsystem));
         VMCOREINFO_OFFSET(dev_printk_info, device);
         VMCOREINFO_LENGTH(printk_info_device, sizeof(dev_info->device));
 
         VMCOREINFO_STRUCT_SIZE(prb_data_ring);
         VMCOREINFO_OFFSET(prb_data_ring, size_bits);
         VMCOREINFO_OFFSET(prb_data_ring, data);
         VMCOREINFO_OFFSET(prb_data_ring, head_lpos);
         VMCOREINFO_OFFSET(prb_data_ring, tail_lpos);
 
         VMCOREINFO_SIZE(atomic_long_t);
         VMCOREINFO_TYPE_OFFSET(atomic_long_t, counter);
 
         VMCOREINFO_STRUCT_SIZE(latched_seq);
         VMCOREINFO_OFFSET(latched_seq, val);
 }
 #endif
 
 /* requested log_buf_len from kernel cmdline */
 static unsigned long __initdata new_log_buf_len;
 
 /* we practice scaling the ring buffer by powers of 2 */
 static void __init log_buf_len_update(u64 size)
 {
         if (size > (u64)LOG_BUF_LEN_MAX) {
                 size = (u64)LOG_BUF_LEN_MAX;
                 pr_err("log_buf over 2G is not supported.\n");
         }
 
         if (size)
                 size = roundup_pow_of_two(size);
         if (size > log_buf_len)
                 new_log_buf_len = (unsigned long)size;
 }
 
 /* save requested log_buf_len since it's too early to process it */
 static int __init log_buf_len_setup(char *str)
 {
         u64 size;
 
         if (!str)
                 return -EINVAL;
 
         size = memparse(str, &str);
 
         log_buf_len_update(size);
 
         return 0;
 }
 early_param("log_buf_len", log_buf_len_setup);
 
 #ifdef CONFIG_SMP
 #define __LOG_CPU_MAX_BUF_LEN (1 << CONFIG_LOG_CPU_MAX_BUF_SHIFT)
 
 static void __init log_buf_add_cpu(void)
 {
         unsigned int cpu_extra;
 
         /*
          * archs should set up cpu_possible_bits properly with
          * set_cpu_possible() after setup_arch() but just in
          * case lets ensure this is valid.
          */
         if (num_possible_cpus() == 1)
                 return;
 
         cpu_extra = (num_possible_cpus() - 1) * __LOG_CPU_MAX_BUF_LEN;
 
         /* by default this will only continue through for large > 64 CPUs */
         if (cpu_extra <= __LOG_BUF_LEN / 2)
                 return;
 
         pr_info("log_buf_len individual max cpu contribution: %d bytes\n",
                 __LOG_CPU_MAX_BUF_LEN);
         pr_info("log_buf_len total cpu_extra contributions: %d bytes\n",
                 cpu_extra);
         pr_info("log_buf_len min size: %d bytes\n", __LOG_BUF_LEN);
 
         log_buf_len_update(cpu_extra + __LOG_BUF_LEN);
 }
 #else /* !CONFIG_SMP */
 static inline void log_buf_add_cpu(void) {}
 #endif /* CONFIG_SMP */
 
 static void __init set_percpu_data_ready(void)
 {
         __printk_percpu_data_ready = true;
 }
 
 static unsigned int __init add_to_rb(struct printk_ringbuffer *rb,
                                      struct printk_record *r)
 {
         struct prb_reserved_entry e;
         struct printk_record dest_r;
 
         prb_rec_init_wr(&dest_r, r->info->text_len);
 
         if (!prb_reserve(&e, rb, &dest_r))
                 return 0;
 
         memcpy(&dest_r.text_buf[0], &r->text_buf[0], r->info->text_len);
         dest_r.info->text_len = r->info->text_len;
         dest_r.info->facility = r->info->facility;
         dest_r.info->level = r->info->level;
         dest_r.info->flags = r->info->flags;
         dest_r.info->ts_nsec = r->info->ts_nsec;
         dest_r.info->caller_id = r->info->caller_id;
         memcpy(&dest_r.info->dev_info, &r->info->dev_info, sizeof(dest_r.info->dev_info));
 
         prb_final_commit(&e);
 
         return prb_record_text_space(&e);
 }
 
 static char setup_text_buf[PRINTKRB_RECORD_MAX] __initdata;
 
 void __init setup_log_buf(int early)
 {
         struct printk_info *new_infos;
         unsigned int new_descs_count;
         struct prb_desc *new_descs;
         struct printk_info info;
         struct printk_record r;
         unsigned int text_size;
         size_t new_descs_size;
         size_t new_infos_size;
         unsigned long flags;
         char *new_log_buf;
         unsigned int free;
         u64 seq;
 
         /*
          * Some archs call setup_log_buf() multiple times - first is very
          * early, e.g. from setup_arch(), and second - when percpu_areas
          * are initialised.
          */
         if (!early)
                 set_percpu_data_ready();
 
         if (log_buf != __log_buf)
                 return;
 
         if (!early && !new_log_buf_len)
                 log_buf_add_cpu();
 
         if (!new_log_buf_len)
                 return;
 
         new_descs_count = new_log_buf_len >> PRB_AVGBITS;
         if (new_descs_count == 0) {
                 pr_err("new_log_buf_len: %lu too small\n", new_log_buf_len);
                 return;
         }
 
         new_log_buf = memblock_alloc(new_log_buf_len, LOG_ALIGN);
         if (unlikely(!new_log_buf)) {
                 pr_err("log_buf_len: %lu text bytes not available\n",
                        new_log_buf_len);
                 return;
         }
 
         new_descs_size = new_descs_count * sizeof(struct prb_desc);
         new_descs = memblock_alloc(new_descs_size, LOG_ALIGN);
         if (unlikely(!new_descs)) {
                 pr_err("log_buf_len: %zu desc bytes not available\n",
                        new_descs_size);
                 goto err_free_log_buf;
         }
 
         new_infos_size = new_descs_count * sizeof(struct printk_info);
         new_infos = memblock_alloc(new_infos_size, LOG_ALIGN);
         if (unlikely(!new_infos)) {
                 pr_err("log_buf_len: %zu info bytes not available\n",
                        new_infos_size);
                 goto err_free_descs;
         }
 
         prb_rec_init_rd(&r, &info, &setup_text_buf[0], sizeof(setup_text_buf));
 
         prb_init(&printk_rb_dynamic,
                  new_log_buf, ilog2(new_log_buf_len),
                  new_descs, ilog2(new_descs_count),
                  new_infos);
 
         local_irq_save(flags);
 
         log_buf_len = new_log_buf_len;
         log_buf = new_log_buf;
         new_log_buf_len = 0;
 
         free = __LOG_BUF_LEN;
         prb_for_each_record(0, &printk_rb_static, seq, &r) {
                 text_size = add_to_rb(&printk_rb_dynamic, &r);
                 if (text_size > free)
                         free = 0;
                 else
                         free -= text_size;
         }
 
         prb = &printk_rb_dynamic;
 
         local_irq_restore(flags);
 
         /*
          * Copy any remaining messages that might have appeared from
          * NMI context after copying but before switching to the
          * dynamic buffer.
          */
         prb_for_each_record(seq, &printk_rb_static, seq, &r) {
                 text_size = add_to_rb(&printk_rb_dynamic, &r);
                 if (text_size > free)
                         free = 0;
                 else
                         free -= text_size;
         }
 
         if (seq != prb_next_seq(&printk_rb_static)) {
                 pr_err("dropped %llu messages\n",
                        prb_next_seq(&printk_rb_static) - seq);
         }
 
         pr_info("log_buf_len: %u bytes\n", log_buf_len);
         pr_info("early log buf free: %u(%u%%)\n",
                 free, (free * 100) / __LOG_BUF_LEN);
         return;
 
 err_free_descs:
         memblock_free(new_descs, new_descs_size);
 err_free_log_buf:
         memblock_free(new_log_buf, new_log_buf_len);
 }
 
 static bool __read_mostly ignore_loglevel;
 
 static int __init ignore_loglevel_setup(char *str)
 {
         ignore_loglevel = true;
         pr_info("debug: ignoring loglevel setting.\n");
 
         return 0;
 }
 
 early_param("ignore_loglevel", ignore_loglevel_setup);
 module_param(ignore_loglevel, bool, S_IRUGO | S_IWUSR);
 MODULE_PARM_DESC(ignore_loglevel,
                  "ignore loglevel setting (prints all kernel messages to the console)");
 
 static bool suppress_message_printing(int level)
 {
         return (level >= console_loglevel && !ignore_loglevel);
 }
 
 #ifdef CONFIG_BOOT_PRINTK_DELAY
 
 static int boot_delay; /* msecs delay after each printk during bootup */
 static unsigned long long loops_per_msec;       /* based on boot_delay */
 
 static int __init boot_delay_setup(char *str)
 {
         unsigned long lpj;
 
         lpj = preset_lpj ? preset_lpj : 1000000;        /* some guess */
         loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
 
         get_option(&str, &boot_delay);
         if (boot_delay > 10 * 1000)
                 boot_delay = 0;
 
         pr_debug("boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
                 "HZ: %d, loops_per_msec: %llu\n",
                 boot_delay, preset_lpj, lpj, HZ, loops_per_msec);
         return 0;
 }
 early_param("boot_delay", boot_delay_setup);
 
 static void boot_delay_msec(int level)
 {
         unsigned long long k;
         unsigned long timeout;
 
         if ((boot_delay == 0 || system_state >= SYSTEM_RUNNING)
                 || suppress_message_printing(level)) {
                 return;
         }
 
         k = (unsigned long long)loops_per_msec * boot_delay;
 
         timeout = jiffies + msecs_to_jiffies(boot_delay);
         while (k) {
                 k--;
                 cpu_relax();
                 /*
                  * use (volatile) jiffies to prevent
                  * compiler reduction; loop termination via jiffies
                  * is secondary and may or may not happen.
                  */
                 if (time_after(jiffies, timeout))
                         break;
                 touch_nmi_watchdog();
         }
 }
 #else
 static inline void boot_delay_msec(int level)
 {
 }
 #endif
 
 static bool printk_time = IS_ENABLED(CONFIG_PRINTK_TIME);
 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
 
 static size_t print_syslog(unsigned int level, char *buf)
 {
         return sprintf(buf, "<%u>", level);
 }
 
 static size_t print_time(u64 ts, char *buf)
 {
         unsigned long rem_nsec = do_div(ts, 1000000000);
 
         return sprintf(buf, "[%5lu.%06lu]",
                        (unsigned long)ts, rem_nsec / 1000);
 }
 
 #ifdef CONFIG_PRINTK_CALLER
 static size_t print_caller(u32 id, char *buf)
 {
         char caller[12];
 
         snprintf(caller, sizeof(caller), "%c%u",
                  id & 0x80000000 ? 'C' : 'T', id & ~0x80000000);
         return sprintf(buf, "[%6s]", caller);
 }
 #else
 #define print_caller(id, buf) 0
 #endif
 
 static size_t info_print_prefix(const struct printk_info  *info, bool syslog,
                                 bool time, char *buf)
 {
         size_t len = 0;
 
         if (syslog)
                 len = print_syslog((info->facility << 3) | info->level, buf);
 
         if (time)
                 len += print_time(info->ts_nsec, buf + len);
 
         len += print_caller(info->caller_id, buf + len);
 
         if (IS_ENABLED(CONFIG_PRINTK_CALLER) || time) {
                 buf[len++] = ' ';
                 buf[len] = '\0';
         }
 
         return len;
 }
 
 /*
  * Prepare the record for printing. The text is shifted within the given
  * buffer to avoid a need for another one. The following operations are
  * done:
  *
  *   - Add prefix for each line.
  *   - Drop truncated lines that no longer fit into the buffer.
  *   - Add the trailing newline that has been removed in vprintk_store().
  *   - Add a string terminator.
  *
  * Since the produced string is always terminated, the maximum possible
  * return value is @r->text_buf_size - 1;
  *
  * Return: The length of the updated/prepared text, including the added
  * prefixes and the newline. The terminator is not counted. The dropped
  * line(s) are not counted.
  */
 static size_t record_print_text(struct printk_record *r, bool syslog,
                                 bool time)
 {
         size_t text_len = r->info->text_len;
         size_t buf_size = r->text_buf_size;
         char *text = r->text_buf;
         char prefix[PRINTK_PREFIX_MAX];
         bool truncated = false;
         size_t prefix_len;
         size_t line_len;
         size_t len = 0;
         char *next;
 
         /*
          * If the message was truncated because the buffer was not large
          * enough, treat the available text as if it were the full text.
          */
         if (text_len > buf_size)
                 text_len = buf_size;
 
         prefix_len = info_print_prefix(r->info, syslog, time, prefix);
 
         /*
          * @text_len: bytes of unprocessed text
          * @line_len: bytes of current line _without_ newline
          * @text:     pointer to beginning of current line
          * @len:      number of bytes prepared in r->text_buf
          */
         for (;;) {
                 next = memchr(text, '\n', text_len);
                 if (next) {
                         line_len = next - text;
                 } else {
                         /* Drop truncated line(s). */
                         if (truncated)
                                 break;
                         line_len = text_len;
                 }
 
                 /*
                  * Truncate the text if there is not enough space to add the
                  * prefix and a trailing newline and a terminator.
                  */
                 if (len + prefix_len + text_len + 1 + 1 > buf_size) {
                         /* Drop even the current line if no space. */
                         if (len + prefix_len + line_len + 1 + 1 > buf_size)
                                 break;
 
                         text_len = buf_size - len - prefix_len - 1 - 1;
                         truncated = true;
                 }
 
                 memmove(text + prefix_len, text, text_len);
                 memcpy(text, prefix, prefix_len);
 
                 /*
                  * Increment the prepared length to include the text and
                  * prefix that were just moved+copied. Also increment for the
                  * newline at the end of this line. If this is the last line,
                  * there is no newline, but it will be added immediately below.
                  */
                 len += prefix_len + line_len + 1;
                 if (text_len == line_len) {
                         /*
                          * This is the last line. Add the trailing newline
                          * removed in vprintk_store().
                          */
                         text[prefix_len + line_len] = '\n';
                         break;
                 }
 
                 /*
                  * Advance beyond the added prefix and the related line with
                  * its newline.
                  */
                 text += prefix_len + line_len + 1;
 
                 /*
                  * The remaining text has only decreased by the line with its
                  * newline.
                  *
                  * Note that @text_len can become zero. It happens when @text
                  * ended with a newline (either due to truncation or the
                  * original string ending with "\n\n"). The loop is correctly
                  * repeated and (if not truncated) an empty line with a prefix
                  * will be prepared.
                  */
                 text_len -= line_len + 1;
         }
 
         /*
          * If a buffer was provided, it will be terminated. Space for the
          * string terminator is guaranteed to be available. The terminator is
          * not counted in the return value.
          */
         if (buf_size > 0)
                 r->text_buf[len] = 0;
 
         return len;
 }
 
 static size_t get_record_print_text_size(struct printk_info *info,
                                          unsigned int line_count,
                                          bool syslog, bool time)
 {
         char prefix[PRINTK_PREFIX_MAX];
         size_t prefix_len;
 
         prefix_len = info_print_prefix(info, syslog, time, prefix);
 
         /*
          * Each line will be preceded with a prefix. The intermediate
          * newlines are already within the text, but a final trailing
          * newline will be added.
          */
         return ((prefix_len * line_count) + info->text_len + 1);
 }
 
 /*
  * Beginning with @start_seq, find the first record where it and all following
  * records up to (but not including) @max_seq fit into @size.
  *
  * @max_seq is simply an upper bound and does not need to exist. If the caller
  * does not require an upper bound, -1 can be used for @max_seq.
  */
 static u64 find_first_fitting_seq(u64 start_seq, u64 max_seq, size_t size,
                                   bool syslog, bool time)
 {
         struct printk_info info;
         unsigned int line_count;
         size_t len = 0;
         u64 seq;
 
         /* Determine the size of the records up to @max_seq. */
         prb_for_each_info(start_seq, prb, seq, &info, &line_count) {
                 if (info.seq >= max_seq)
                         break;
                 len += get_record_print_text_size(&info, line_count, syslog, time);
         }
 
         /*
          * Adjust the upper bound for the next loop to avoid subtracting
          * lengths that were never added.
          */
         if (seq < max_seq)
                 max_seq = seq;
 
         /*
          * Move first record forward until length fits into the buffer. Ignore
          * newest messages that were not counted in the above cycle. Messages
          * might appear and get lost in the meantime. This is a best effort
          * that prevents an infinite loop that could occur with a retry.
          */
         prb_for_each_info(start_seq, prb, seq, &info, &line_count) {
                 if (len <= size || info.seq >= max_seq)
                         break;
                 len -= get_record_print_text_size(&info, line_count, syslog, time);
         }
 
         return seq;
 }
 
 /* The caller is responsible for making sure @size is greater than 0. */
 static int syslog_print(char __user *buf, int size)
 {
         struct printk_info info;
         struct printk_record r;
         char *text;
         int len = 0;
         u64 seq;
 
         text = kmalloc(PRINTK_MESSAGE_MAX, GFP_KERNEL);
         if (!text)
                 return -ENOMEM;
 
         prb_rec_init_rd(&r, &info, text, PRINTK_MESSAGE_MAX);
 
         mutex_lock(&syslog_lock);
 
         /*
          * Wait for the @syslog_seq record to be available. @syslog_seq may
          * change while waiting.
          */
         do {
                 seq = syslog_seq;
 
                 mutex_unlock(&syslog_lock);
                 /*
                  * Guarantee this task is visible on the waitqueue before
                  * checking the wake condition.
                  *
                  * The full memory barrier within set_current_state() of
                  * prepare_to_wait_event() pairs with the full memory barrier
                  * within wq_has_sleeper().
                  *
                  * This pairs with __wake_up_klogd:A.
                  */
                 len = wait_event_interruptible(log_wait,
                                 prb_read_valid(prb, seq, NULL)); /* LMM(syslog_print:A) */
                 mutex_lock(&syslog_lock);
 
                 if (len)
                         goto out;
         } while (syslog_seq != seq);
 
         /*
          * Copy records that fit into the buffer. The above cycle makes sure
          * that the first record is always available.
          */
         do {
                 size_t n;
                 size_t skip;
                 int err;
 
                 if (!prb_read_valid(prb, syslog_seq, &r))
                         break;
 
                 if (r.info->seq != syslog_seq) {
                         /* message is gone, move to next valid one */
                         syslog_seq = r.info->seq;
                         syslog_partial = 0;
                 }
 
                 /*
                  * To keep reading/counting partial line consistent,
                  * use printk_time value as of the beginning of a line.
                  */
                 if (!syslog_partial)
                         syslog_time = printk_time;
 
                 skip = syslog_partial;
                 n = record_print_text(&r, true, syslog_time);
                 if (n - syslog_partial <= size) {
                         /* message fits into buffer, move forward */
                         syslog_seq = r.info->seq + 1;
                         n -= syslog_partial;
                         syslog_partial = 0;
                 } else if (!len){
                         /* partial read(), remember position */
                         n = size;
                         syslog_partial += n;
                 } else
                         n = 0;
 
                 if (!n)
                         break;
 
                 mutex_unlock(&syslog_lock);
                 err = copy_to_user(buf, text + skip, n);
                 mutex_lock(&syslog_lock);
 
                 if (err) {
                         if (!len)
                                 len = -EFAULT;
                         break;
                 }
 
                 len += n;
                 size -= n;
                 buf += n;
         } while (size);
 out:
         mutex_unlock(&syslog_lock);
         kfree(text);
         return len;
 }
 
 static int syslog_print_all(char __user *buf, int size, bool clear)
 {
         struct printk_info info;
         struct printk_record r;
         char *text;
         int len = 0;
         u64 seq;
         bool time;
 
         text = kmalloc(PRINTK_MESSAGE_MAX, GFP_KERNEL);
         if (!text)
                 return -ENOMEM;
 
         time = printk_time;
         /*
          * Find first record that fits, including all following records,
          * into the user-provided buffer for this dump.
          */
         seq = find_first_fitting_seq(latched_seq_read_nolock(&clear_seq), -1,
                                      size, true, time);
 
         prb_rec_init_rd(&r, &info, text, PRINTK_MESSAGE_MAX);
 
         prb_for_each_record(seq, prb, seq, &r) {
                 int textlen;
 
                 textlen = record_print_text(&r, true, time);
 
                 if (len + textlen > size) {
                         seq--;
                         break;
                 }
 
                 if (copy_to_user(buf + len, text, textlen))
                         len = -EFAULT;
                 else
                         len += textlen;
 
                 if (len < 0)
                         break;
         }
 
         if (clear) {
                 mutex_lock(&syslog_lock);
                 latched_seq_write(&clear_seq, seq);
                 mutex_unlock(&syslog_lock);
         }
 
         kfree(text);
         return len;
 }
 
 static void syslog_clear(void)
 {
         mutex_lock(&syslog_lock);
         latched_seq_write(&clear_seq, prb_next_seq(prb));
         mutex_unlock(&syslog_lock);
 }
 
 int do_syslog(int type, char __user *buf, int len, int source)
 {
         struct printk_info info;
         bool clear = false;
         static int saved_console_loglevel = LOGLEVEL_DEFAULT;
         int error;
 
         error = check_syslog_permissions(type, source);
         if (error)
                 return error;
 
         switch (type) {
         case SYSLOG_ACTION_CLOSE:       /* Close log */
                 break;
         case SYSLOG_ACTION_OPEN:        /* Open log */
                 break;
         case SYSLOG_ACTION_READ:        /* Read from log */
                 if (!buf || len < 0)
                         return -EINVAL;
                 if (!len)
                         return 0;
                 if (!access_ok(buf, len))
                         return -EFAULT;
                 error = syslog_print(buf, len);
                 break;
         /* Read/clear last kernel messages */
         case SYSLOG_ACTION_READ_CLEAR:
                 clear = true;
                 fallthrough;
         /* Read last kernel messages */
         case SYSLOG_ACTION_READ_ALL:
                 if (!buf || len < 0)
                         return -EINVAL;
                 if (!len)
                         return 0;
                 if (!access_ok(buf, len))
                         return -EFAULT;
                 error = syslog_print_all(buf, len, clear);
                 break;
         /* Clear ring buffer */
         case SYSLOG_ACTION_CLEAR:
                 syslog_clear();
                 break;
         /* Disable logging to console */
         case SYSLOG_ACTION_CONSOLE_OFF:
                 if (saved_console_loglevel == LOGLEVEL_DEFAULT)
                         saved_console_loglevel = console_loglevel;
                 console_loglevel = minimum_console_loglevel;
                 break;
         /* Enable logging to console */
         case SYSLOG_ACTION_CONSOLE_ON:
                 if (saved_console_loglevel != LOGLEVEL_DEFAULT) {
                         console_loglevel = saved_console_loglevel;
                         saved_console_loglevel = LOGLEVEL_DEFAULT;
                 }
                 break;
         /* Set level of messages printed to console */
         case SYSLOG_ACTION_CONSOLE_LEVEL:
                 if (len < 1 || len > 8)
                         return -EINVAL;
                 if (len < minimum_console_loglevel)
                         len = minimum_console_loglevel;
                 console_loglevel = len;
                 /* Implicitly re-enable logging to console */
                 saved_console_loglevel = LOGLEVEL_DEFAULT;
                 break;
         /* Number of chars in the log buffer */
         case SYSLOG_ACTION_SIZE_UNREAD:
                 mutex_lock(&syslog_lock);
                 if (!prb_read_valid_info(prb, syslog_seq, &info, NULL)) {
                         /* No unread messages. */
                         mutex_unlock(&syslog_lock);
                         return 0;
                 }
                 if (info.seq != syslog_seq) {
                         /* messages are gone, move to first one */
                         syslog_seq = info.seq;
                         syslog_partial = 0;
                 }
                 if (source == SYSLOG_FROM_PROC) {
                         /*
                          * Short-cut for poll(/"proc/kmsg") which simply checks
                          * for pending data, not the size; return the count of
                          * records, not the length.
                          */
                         error = prb_next_seq(prb) - syslog_seq;
                 } else {
                         bool time = syslog_partial ? syslog_time : printk_time;
                         unsigned int line_count;
                         u64 seq;
 
                         prb_for_each_info(syslog_seq, prb, seq, &info,
                                           &line_count) {
                                 error += get_record_print_text_size(&info, line_count,
                                                                     true, time);
                                 time = printk_time;
                         }
                         error -= syslog_partial;
                 }
                 mutex_unlock(&syslog_lock);
                 break;
         /* Size of the log buffer */
         case SYSLOG_ACTION_SIZE_BUFFER:
                 error = log_buf_len;
                 break;
         default:
                 error = -EINVAL;
                 break;
         }
 
         return error;
 }
 
 SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
 {
         return do_syslog(type, buf, len, SYSLOG_FROM_READER);
 }
 
 /*
  * Special console_lock variants that help to reduce the risk of soft-lockups.
  * They allow to pass console_lock to another printk() call using a busy wait.
  */
 
 #ifdef CONFIG_LOCKDEP
 static struct lockdep_map console_owner_dep_map = {
         .name = "console_owner"
 };
 #endif
 
 static DEFINE_RAW_SPINLOCK(console_owner_lock);
 static struct task_struct *console_owner;
 static bool console_waiter;
 
 /**
  * console_lock_spinning_enable - mark beginning of code where another
  *      thread might safely busy wait
  *
  * This basically converts console_lock into a spinlock. This marks
  * the section where the console_lock owner can not sleep, because
  * there may be a waiter spinning (like a spinlock). Also it must be
  * ready to hand over the lock at the end of the section.
  */
 static void console_lock_spinning_enable(void)
 {
         /*
          * Do not use spinning in panic(). The panic CPU wants to keep the lock.
          * Non-panic CPUs abandon the flush anyway.
          *
          * Just keep the lockdep annotation. The panic-CPU should avoid
          * taking console_owner_lock because it might cause a deadlock.
          * This looks like the easiest way how to prevent false lockdep
          * reports without handling races a lockless way.
          */
         if (panic_in_progress())
                 goto lockdep;
 
         raw_spin_lock(&console_owner_lock);
         console_owner = current;
         raw_spin_unlock(&console_owner_lock);
 
 lockdep:
         /* The waiter may spin on us after setting console_owner */
         spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_);
 }
 
 /**
  * console_lock_spinning_disable_and_check - mark end of code where another
  *      thread was able to busy wait and check if there is a waiter
  * @cookie: cookie returned from console_srcu_read_lock()
  *
  * This is called at the end of the section where spinning is allowed.
  * It has two functions. First, it is a signal that it is no longer
  * safe to start busy waiting for the lock. Second, it checks if
  * there is a busy waiter and passes the lock rights to her.
  *
  * Important: Callers lose both the console_lock and the SRCU read lock if
  *      there was a busy waiter. They must not touch items synchronized by
  *      console_lock or SRCU read lock in this case.
  *
  * Return: 1 if the lock rights were passed, 0 otherwise.
  */
 static int console_lock_spinning_disable_and_check(int cookie)
 {
         int waiter;
 
         /*
          * Ignore spinning waiters during panic() because they might get stopped
          * or blocked at any time,
          *
          * It is safe because nobody is allowed to start spinning during panic
          * in the first place. If there has been a waiter then non panic CPUs
          * might stay spinning. They would get stopped anyway. The panic context
          * will never start spinning and an interrupted spin on panic CPU will
          * never continue.
          */
         if (panic_in_progress()) {
                 /* Keep lockdep happy. */
                 spin_release(&console_owner_dep_map, _THIS_IP_);
                 return 0;
         }
 
         raw_spin_lock(&console_owner_lock);
         waiter = READ_ONCE(console_waiter);
         console_owner = NULL;
         raw_spin_unlock(&console_owner_lock);
 
         if (!waiter) {
                 spin_release(&console_owner_dep_map, _THIS_IP_);
                 return 0;
         }
 
         /* The waiter is now free to continue */
         WRITE_ONCE(console_waiter, false);
 
         spin_release(&console_owner_dep_map, _THIS_IP_);
 
         /*
          * Preserve lockdep lock ordering. Release the SRCU read lock before
          * releasing the console_lock.
          */
         console_srcu_read_unlock(cookie);
 
         /*
          * Hand off console_lock to waiter. The waiter will perform
          * the up(). After this, the waiter is the console_lock owner.
          */
         mutex_release(&console_lock_dep_map, _THIS_IP_);
         return 1;
 }
 
 /**
  * console_trylock_spinning - try to get console_lock by busy waiting
  *
  * This allows to busy wait for the console_lock when the current
  * owner is running in specially marked sections. It means that
  * the current owner is running and cannot reschedule until it
  * is ready to lose the lock.
  *
  * Return: 1 if we got the lock, 0 othrewise
  */
 static int console_trylock_spinning(void)
 {
         struct task_struct *owner = NULL;
         bool waiter;
         bool spin = false;
         unsigned long flags;
 
         if (console_trylock())
                 return 1;
 
         /*
          * It's unsafe to spin once a panic has begun. If we are the
          * panic CPU, we may have already halted the owner of the
          * console_sem. If we are not the panic CPU, then we should
          * avoid taking console_sem, so the panic CPU has a better
          * chance of cleanly acquiring it later.
          */
         if (panic_in_progress())
                 return 0;
 
         printk_safe_enter_irqsave(flags);
 
         raw_spin_lock(&console_owner_lock);
         owner = READ_ONCE(console_owner);
         waiter = READ_ONCE(console_waiter);
         if (!waiter && owner && owner != current) {
                 WRITE_ONCE(console_waiter, true);
                 spin = true;
         }
         raw_spin_unlock(&console_owner_lock);
 
         /*
          * If there is an active printk() writing to the
          * consoles, instead of having it write our data too,
          * see if we can offload that load from the active
          * printer, and do some printing ourselves.
          * Go into a spin only if there isn't already a waiter
          * spinning, and there is an active printer, and
          * that active printer isn't us (recursive printk?).
          */
         if (!spin) {
                 printk_safe_exit_irqrestore(flags);
                 return 0;
         }
 
         /* We spin waiting for the owner to release us */
         spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_);
         /* Owner will clear console_waiter on hand off */
         while (READ_ONCE(console_waiter))
                 cpu_relax();
         spin_release(&console_owner_dep_map, _THIS_IP_);
 
         printk_safe_exit_irqrestore(flags);
         /*
          * The owner passed the console lock to us.
          * Since we did not spin on console lock, annotate
          * this as a trylock. Otherwise lockdep will
          * complain.
          */
         mutex_acquire(&console_lock_dep_map, 0, 1, _THIS_IP_);
 
         /*
          * Update @console_may_schedule for trylock because the previous
          * owner may have been schedulable.
          */
         console_may_schedule = 0;
 
         return 1;
 }
 
 /*
  * Recursion is tracked separately on each CPU. If NMIs are supported, an
  * additional NMI context per CPU is also separately tracked. Until per-CPU
  * is available, a separate "early tracking" is performed.
  */
 static DEFINE_PER_CPU(u8, printk_count);
 static u8 printk_count_early;
 #ifdef CONFIG_HAVE_NMI
 static DEFINE_PER_CPU(u8, printk_count_nmi);
 static u8 printk_count_nmi_early;
 #endif
 
 /*
  * Recursion is limited to keep the output sane. printk() should not require
  * more than 1 level of recursion (allowing, for example, printk() to trigger
  * a WARN), but a higher value is used in case some printk-internal errors
  * exist, such as the ringbuffer validation checks failing.
  */
 #define PRINTK_MAX_RECURSION 3
 
 /*
  * Return a pointer to the dedicated counter for the CPU+context of the
  * caller.
  */
 static u8 *__printk_recursion_counter(void)
 {
 #ifdef CONFIG_HAVE_NMI
         if (in_nmi()) {
                 if (printk_percpu_data_ready())
                         return this_cpu_ptr(&printk_count_nmi);
                 return &printk_count_nmi_early;
         }
 #endif
         if (printk_percpu_data_ready())
                 return this_cpu_ptr(&printk_count);
         return &printk_count_early;
 }
 
 /*
  * Enter recursion tracking. Interrupts are disabled to simplify tracking.
  * The caller must check the boolean return value to see if the recursion is
  * allowed. On failure, interrupts are not disabled.
  *
  * @recursion_ptr must be a variable of type (u8 *) and is the same variable
  * that is passed to printk_exit_irqrestore().
  */
 #define printk_enter_irqsave(recursion_ptr, flags)      \
 ({                                                      \
         bool success = true;                            \
                                                         \
         typecheck(u8 *, recursion_ptr);                 \
         local_irq_save(flags);                          \
         (recursion_ptr) = __printk_recursion_counter(); \
         if (*(recursion_ptr) > PRINTK_MAX_RECURSION) {  \
                 local_irq_restore(flags);               \
                 success = false;                        \
         } else {                                        \
                 (*(recursion_ptr))++;                   \
         }                                               \
         success;                                        \
 })
 
 /* Exit recursion tracking, restoring interrupts. */
 #define printk_exit_irqrestore(recursion_ptr, flags)    \
         do {                                            \
                 typecheck(u8 *, recursion_ptr);         \
                 (*(recursion_ptr))--;                   \
                 local_irq_restore(flags);               \
         } while (0)
 
 int printk_delay_msec __read_mostly;
 
 static inline void printk_delay(int level)
 {
         boot_delay_msec(level);
 
         if (unlikely(printk_delay_msec)) {
                 int m = printk_delay_msec;
 
                 while (m--) {
                         mdelay(1);
                         touch_nmi_watchdog();
                 }
         }
 }
 
 static inline u32 printk_caller_id(void)
 {
         return in_task() ? task_pid_nr(current) :
                 0x80000000 + smp_processor_id();
 }
 
 /**
  * printk_parse_prefix - Parse level and control flags.
  *
  * @text:     The terminated text message.
  * @level:    A pointer to the current level value, will be updated.
  * @flags:    A pointer to the current printk_info flags, will be updated.
  *
  * @level may be NULL if the caller is not interested in the parsed value.
  * Otherwise the variable pointed to by @level must be set to
  * LOGLEVEL_DEFAULT in order to be updated with the parsed value.
  *
  * @flags may be NULL if the caller is not interested in the parsed value.
  * Otherwise the variable pointed to by @flags will be OR'd with the parsed
  * value.
  *
  * Return: The length of the parsed level and control flags.
  */
 u16 printk_parse_prefix(const char *text, int *level,
                         enum printk_info_flags *flags)
 {
         u16 prefix_len = 0;
         int kern_level;
 
         while (*text) {
                 kern_level = printk_get_level(text);
                 if (!kern_level)
                         break;
 
                 switch (kern_level) {
                 case '' ... '7':
                         if (level && *level == LOGLEVEL_DEFAULT)
                                 *level = kern_level - '';
                         break;
                 case 'c':       /* KERN_CONT */
                         if (flags)
                                 *flags |= LOG_CONT;
                 }
 
                 prefix_len += 2;
                 text += 2;
         }
 
         return prefix_len;
 }
 
 __printf(5, 0)
 static u16 printk_sprint(char *text, u16 size, int facility,
                          enum printk_info_flags *flags, const char *fmt,
                          va_list args)
 {
         u16 text_len;
 
         text_len = vscnprintf(text, size, fmt, args);
 
         /* Mark and strip a trailing newline. */
         if (text_len && text[text_len - 1] == '\n') {
                 text_len--;
                 *flags |= LOG_NEWLINE;
         }
 
         /* Strip log level and control flags. */
         if (facility == 0) {
                 u16 prefix_len;
 
                 prefix_len = printk_parse_prefix(text, NULL, NULL);
                 if (prefix_len) {
                         text_len -= prefix_len;
                         memmove(text, text + prefix_len, text_len);
                 }
         }
 
         trace_console(text, text_len);
 
         return text_len;
 }
 
 __printf(4, 0)
 int vprintk_store(int facility, int level,
                   const struct dev_printk_info *dev_info,
                   const char *fmt, va_list args)
 {
         struct prb_reserved_entry e;
         enum printk_info_flags flags = 0;
         struct printk_record r;
         unsigned long irqflags;
         u16 trunc_msg_len = 0;
         char prefix_buf[8];
         u8 *recursion_ptr;
         u16 reserve_size;
         va_list args2;
         u32 caller_id;
         u16 text_len;
         int ret = 0;
         u64 ts_nsec;
 
         if (!printk_enter_irqsave(recursion_ptr, irqflags))
                 return 0;
 
         /*
          * Since the duration of printk() can vary depending on the message
          * and state of the ringbuffer, grab the timestamp now so that it is
          * close to the call of printk(). This provides a more deterministic
          * timestamp with respect to the caller.
          */
         ts_nsec = local_clock();
 
         caller_id = printk_caller_id();
 
         /*
          * The sprintf needs to come first since the syslog prefix might be
          * passed in as a parameter. An extra byte must be reserved so that
          * later the vscnprintf() into the reserved buffer has room for the
          * terminating '\0', which is not counted by vsnprintf().
          */
         va_copy(args2, args);
         reserve_size = vsnprintf(&prefix_buf[0], sizeof(prefix_buf), fmt, args2) + 1;
         va_end(args2);
 
         if (reserve_size > PRINTKRB_RECORD_MAX)
                 reserve_size = PRINTKRB_RECORD_MAX;
 
         /* Extract log level or control flags. */
         if (facility == 0)
                 printk_parse_prefix(&prefix_buf[0], &level, &flags);
 
         if (level == LOGLEVEL_DEFAULT)
                 level = default_message_loglevel;
 
         if (dev_info)
                 flags |= LOG_NEWLINE;
 
         if (flags & LOG_CONT) {
                 prb_rec_init_wr(&r, reserve_size);
                 if (prb_reserve_in_last(&e, prb, &r, caller_id, PRINTKRB_RECORD_MAX)) {
                         text_len = printk_sprint(&r.text_buf[r.info->text_len], reserve_size,
                                                  facility, &flags, fmt, args);
                         r.info->text_len += text_len;
 
                         if (flags & LOG_NEWLINE) {
                                 r.info->flags |= LOG_NEWLINE;
                                 prb_final_commit(&e);
                         } else {
                                 prb_commit(&e);
                         }
 
                         ret = text_len;
                         goto out;
                 }
         }
 
         /*
          * Explicitly initialize the record before every prb_reserve() call.
          * prb_reserve_in_last() and prb_reserve() purposely invalidate the
          * structure when they fail.
          */
         prb_rec_init_wr(&r, reserve_size);
         if (!prb_reserve(&e, prb, &r)) {
                 /* truncate the message if it is too long for empty buffer */
                 truncate_msg(&reserve_size, &trunc_msg_len);
 
                 prb_rec_init_wr(&r, reserve_size + trunc_msg_len);
                 if (!prb_reserve(&e, prb, &r))
                         goto out;
         }
 
         /* fill message */
         text_len = printk_sprint(&r.text_buf[0], reserve_size, facility, &flags, fmt, args);
         if (trunc_msg_len)
                 memcpy(&r.text_buf[text_len], trunc_msg, trunc_msg_len);
         r.info->text_len = text_len + trunc_msg_len;
         r.info->facility = facility;
         r.info->level = level & 7;
         r.info->flags = flags & 0x1f;
         r.info->ts_nsec = ts_nsec;
         r.info->caller_id = caller_id;
         if (dev_info)
                 memcpy(&r.info->dev_info, dev_info, sizeof(r.info->dev_info));
 
         /* A message without a trailing newline can be continued. */
         if (!(flags & LOG_NEWLINE))
                 prb_commit(&e);
         else
                 prb_final_commit(&e);
 
         ret = text_len + trunc_msg_len;
 out:
         printk_exit_irqrestore(recursion_ptr, irqflags);
         return ret;
 }
 
 asmlinkage int vprintk_emit(int facility, int level,
                             const struct dev_printk_info *dev_info,
                             const char *fmt, va_list args)
 {
         int printed_len;
         bool in_sched = false;
 
         /* Suppress unimportant messages after panic happens */
         if (unlikely(suppress_printk))
                 return 0;
 
         /*
          * The messages on the panic CPU are the most important. If
          * non-panic CPUs are generating any messages, they will be
          * silently dropped.
          */
         if (other_cpu_in_panic() && !panic_triggering_all_cpu_backtrace)
                 return 0;
 
         if (level == LOGLEVEL_SCHED) {
                 level = LOGLEVEL_DEFAULT;
                 in_sched = true;
         }
 
         printk_delay(level);
 
         printed_len = vprintk_store(facility, level, dev_info, fmt, args);
 
         /* If called from the scheduler, we can not call up(). */
         if (!in_sched) {
                 /*
                  * The caller may be holding system-critical or
                  * timing-sensitive locks. Disable preemption during
                  * printing of all remaining records to all consoles so that
                  * this context can return as soon as possible. Hopefully
                  * another printk() caller will take over the printing.
                  */
                 preempt_disable();
                 /*
                  * Try to acquire and then immediately release the console
                  * semaphore. The release will print out buffers. With the
                  * spinning variant, this context tries to take over the
                  * printing from another printing context.
                  */
                 if (console_trylock_spinning())
                         console_unlock();
                 preempt_enable();
         }
 
         if (in_sched)
                 defer_console_output();
         else
                 wake_up_klogd();
 
         return printed_len;
 }
 EXPORT_SYMBOL(vprintk_emit);
 
 int vprintk_default(const char *fmt, va_list args)
 {
         return vprintk_emit(0, LOGLEVEL_DEFAULT, NULL, fmt, args);
 }
 EXPORT_SYMBOL_GPL(vprintk_default);
 
 asmlinkage __visible int _printk(const char *fmt, ...)
 {
         va_list args;
         int r;
 
         va_start(args, fmt);
         r = vprintk(fmt, args);
         va_end(args);
 
         return r;
 }
 EXPORT_SYMBOL(_printk);
 
 static bool pr_flush(int timeout_ms, bool reset_on_progress);
 static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress);
 
 #else /* CONFIG_PRINTK */
 
 #define printk_time             false
 
 #define prb_read_valid(rb, seq, r)      false
 #define prb_first_valid_seq(rb)         0
 #define prb_next_seq(rb)                0
 
 static u64 syslog_seq;
 
 static bool pr_flush(int timeout_ms, bool reset_on_progress) { return true; }
 static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress) { return true; }
 
 #endif /* CONFIG_PRINTK */
 
 #ifdef CONFIG_EARLY_PRINTK
 struct console *early_console;
 
 asmlinkage __visible void early_printk(const char *fmt, ...)
 {
         va_list ap;
         char buf[512];
         int n;
 
         if (!early_console)
                 return;
 
         va_start(ap, fmt);
         n = vscnprintf(buf, sizeof(buf), fmt, ap);
         va_end(ap);
 
         early_console->write(early_console, buf, n);
 }
 #endif
 
 static void set_user_specified(struct console_cmdline *c, bool user_specified)
 {
         if (!user_specified)
                 return;
 
         /*
          * @c console was defined by the user on the command line.
          * Do not clear when added twice also by SPCR or the device tree.
          */
         c->user_specified = true;
         /* At least one console defined by the user on the command line. */
         console_set_on_cmdline = 1;
 }
 
 static int __add_preferred_console(const char *name, const short idx,
                                    const char *devname, char *options,
                                    char *brl_options, bool user_specified)
 {
         struct console_cmdline *c;
         int i;
 
         if (!name && !devname)
                 return -EINVAL;
 
         /*
          * We use a signed short index for struct console for device drivers to
          * indicate a not yet assigned index or port. However, a negative index
          * value is not valid when the console name and index are defined on
          * the command line.
          */
         if (name && idx < 0)
                 return -EINVAL;
 
         /*
          *      See if this tty is not yet registered, and
          *      if we have a slot free.
          */
         for (i = 0, c = console_cmdline;
              i < MAX_CMDLINECONSOLES && (c->name[0] || c->devname[0]);
              i++, c++) {
                 if ((name && strcmp(c->name, name) == 0 && c->index == idx) ||
                     (devname && strcmp(c->devname, devname) == 0)) {
                         if (!brl_options)
                                 preferred_console = i;
                         set_user_specified(c, user_specified);
                         return 0;
                 }
         }
         if (i == MAX_CMDLINECONSOLES)
                 return -E2BIG;
         if (!brl_options)
                 preferred_console = i;
         if (name)
                 strscpy(c->name, name);
         if (devname)
                 strscpy(c->devname, devname);
         c->options = options;
         set_user_specified(c, user_specified);
         braille_set_options(c, brl_options);
 
         c->index = idx;
         return 0;
 }
 
 static int __init console_msg_format_setup(char *str)
 {
         if (!strcmp(str, "syslog"))
                 console_msg_format = MSG_FORMAT_SYSLOG;
         if (!strcmp(str, "default"))
                 console_msg_format = MSG_FORMAT_DEFAULT;
         return 1;
 }
 __setup("console_msg_format=", console_msg_format_setup);
 
 /*
  * Set up a console.  Called via do_early_param() in init/main.c
  * for each "console=" parameter in the boot command line.
  */
 static int __init console_setup(char *str)
 {
         static_assert(sizeof(console_cmdline[0].devname) >= sizeof(console_cmdline[0].name) + 4);
         char buf[sizeof(console_cmdline[0].devname)];
         char *brl_options = NULL;
         char *ttyname = NULL;
         char *devname = NULL;
         char *options;
         char *s;
         int idx;
 
         /*
          * console="" or console=null have been suggested as a way to
          * disable console output. Use ttynull that has been created
          * for exactly this purpose.
          */
         if (str[0] == 0 || strcmp(str, "null") == 0) {
                 __add_preferred_console("ttynull", 0, NULL, NULL, NULL, true);
                 return 1;
         }
 
         if (_braille_console_setup(&str, &brl_options))
                 return 1;
 
         /* For a DEVNAME:0.0 style console the character device is unknown early */
         if (strchr(str, ':'))
                 devname = buf;
         else
                 ttyname = buf;
 
         /*
          * Decode str into name, index, options.
          */
         if (ttyname && isdigit(str[0]))
                 scnprintf(buf, sizeof(buf), "ttyS%s", str);
         else
                 strscpy(buf, str);
 
         options = strchr(str, ',');
         if (options)
                 *(options++) = 0;
 
 #ifdef __sparc__
         if (!strcmp(str, "ttya"))
                 strscpy(buf, "ttyS0");
         if (!strcmp(str, "ttyb"))
                 strscpy(buf, "ttyS1");
 #endif
 
         for (s = buf; *s; s++)
                 if ((ttyname && isdigit(*s)) || *s == ',')
                         break;
 
         /* @idx will get defined when devname matches. */
         if (devname)
                 idx = -1;
         else
                 idx = simple_strtoul(s, NULL, 10);
 
         *s = 0;
 
         __add_preferred_console(ttyname, idx, devname, options, brl_options, true);
         return 1;
 }
 __setup("console=", console_setup);
 
 /**
  * add_preferred_console - add a device to the list of preferred consoles.
  * @name: device name
  * @idx: device index
  * @options: options for this console
  *
  * The last preferred console added will be used for kernel messages
  * and stdin/out/err for init.  Normally this is used by console_setup
  * above to handle user-supplied console arguments; however it can also
  * be used by arch-specific code either to override the user or more
  * commonly to provide a default console (ie from PROM variables) when
  * the user has not supplied one.
  */
 int add_preferred_console(const char *name, const short idx, char *options)
 {
         return __add_preferred_console(name, idx, NULL, options, NULL, false);
 }
 
 /**
  * match_devname_and_update_preferred_console - Update a preferred console
  *      when matching devname is found.
  * @devname: DEVNAME:0.0 style device name
  * @name: Name of the corresponding console driver, e.g. "ttyS"
  * @idx: Console index, e.g. port number.
  *
  * The function checks whether a device with the given @devname is
  * preferred via the console=DEVNAME:0.0 command line option.
  * It fills the missing console driver name and console index
  * so that a later register_console() call could find (match)
  * and enable this device.
  *
  * It might be used when a driver subsystem initializes particular
  * devices with already known DEVNAME:0.0 style names. And it
  * could predict which console driver name and index this device
  * would later get associated with.
  *
  * Return: 0 on success, negative error code on failure.
  */
 int match_devname_and_update_preferred_console(const char *devname,
                                                const char *name,
                                                const short idx)
 {
         struct console_cmdline *c = console_cmdline;
         int i;
 
         if (!devname || !strlen(devname) || !name || !strlen(name) || idx < 0)
                 return -EINVAL;
 
         for (i = 0; i < MAX_CMDLINECONSOLES && (c->name[0] || c->devname[0]);
              i++, c++) {
                 if (!strcmp(devname, c->devname)) {
                         pr_info("associate the preferred console \"%s\" with \"%s%d\"\n",
                                 devname, name, idx);
                         strscpy(c->name, name);
                         c->index = idx;
                         return 0;
                 }
         }
 
         return -ENOENT;
 }
 EXPORT_SYMBOL_GPL(match_devname_and_update_preferred_console);
 
 bool console_suspend_enabled = true;
 EXPORT_SYMBOL(console_suspend_enabled);
 
 static int __init console_suspend_disable(char *str)
 {
         console_suspend_enabled = false;
         return 1;
 }
 __setup("no_console_suspend", console_suspend_disable);
 module_param_named(console_suspend, console_suspend_enabled,
                 bool, S_IRUGO | S_IWUSR);
 MODULE_PARM_DESC(console_suspend, "suspend console during suspend"
         " and hibernate operations");
 
 static bool printk_console_no_auto_verbose;
 
 void console_verbose(void)
 {
         if (console_loglevel && !printk_console_no_auto_verbose)
                 console_loglevel = CONSOLE_LOGLEVEL_MOTORMOUTH;
 }
 EXPORT_SYMBOL_GPL(console_verbose);
 
 module_param_named(console_no_auto_verbose, printk_console_no_auto_verbose, bool, 0644);
 MODULE_PARM_DESC(console_no_auto_verbose, "Disable console loglevel raise to highest on oops/panic/etc");
 
 /**
  * suspend_console - suspend the console subsystem
  *
  * This disables printk() while we go into suspend states
  */
 void suspend_console(void)
 {
         struct console *con;
 
         if (!console_suspend_enabled)
                 return;
         pr_info("Suspending console(s) (use no_console_suspend to debug)\n");
         pr_flush(1000, true);
 
         console_list_lock();
         for_each_console(con)
                 console_srcu_write_flags(con, con->flags | CON_SUSPENDED);
         console_list_unlock();
 
         /*
          * Ensure that all SRCU list walks have completed. All printing
          * contexts must be able to see that they are suspended so that it
          * is guaranteed that all printing has stopped when this function
          * completes.
          */
         synchronize_srcu(&console_srcu);
 }
 
 void resume_console(void)
 {
         struct console *con;
 
         if (!console_suspend_enabled)
                 return;
 
         console_list_lock();
         for_each_console(con)
                 console_srcu_write_flags(con, con->flags & ~CON_SUSPENDED);
         console_list_unlock();
 
         /*
          * Ensure that all SRCU list walks have completed. All printing
          * contexts must be able to see they are no longer suspended so
          * that they are guaranteed to wake up and resume printing.
          */
         synchronize_srcu(&console_srcu);
 
         pr_flush(1000, true);
 }
 
 /**
  * console_cpu_notify - print deferred console messages after CPU hotplug
  * @cpu: unused
  *
  * If printk() is called from a CPU that is not online yet, the messages
  * will be printed on the console only if there are CON_ANYTIME consoles.
  * This function is called when a new CPU comes online (or fails to come
  * up) or goes offline.
  */
 static int console_cpu_notify(unsigned int cpu)
 {
         if (!cpuhp_tasks_frozen) {
                 /* If trylock fails, someone else is doing the printing */
                 if (console_trylock())
                         console_unlock();
         }
         return 0;
 }
 
 /**
  * console_lock - block the console subsystem from printing
  *
  * Acquires a lock which guarantees that no consoles will
  * be in or enter their write() callback.
  *
  * Can sleep, returns nothing.
  */
 void console_lock(void)
 {
         might_sleep();
 
         /* On panic, the console_lock must be left to the panic cpu. */
         while (other_cpu_in_panic())
                 msleep(1000);
 
         down_console_sem();
         console_locked = 1;
         console_may_schedule = 1;
 }
 EXPORT_SYMBOL(console_lock);
 
 /**
  * console_trylock - try to block the console subsystem from printing
  *
  * Try to acquire a lock which guarantees that no consoles will
  * be in or enter their write() callback.
  *
  * returns 1 on success, and 0 on failure to acquire the lock.
  */
 int console_trylock(void)
 {
         /* On panic, the console_lock must be left to the panic cpu. */
         if (other_cpu_in_panic())
                 return 0;
         if (down_trylock_console_sem())
                 return 0;
         console_locked = 1;
         console_may_schedule = 0;
         return 1;
 }
 EXPORT_SYMBOL(console_trylock);
 
 int is_console_locked(void)
 {
         return console_locked;
 }
 EXPORT_SYMBOL(is_console_locked);
 
 /*
  * Check if the given console is currently capable and allowed to print
  * records.
  *
  * Requires the console_srcu_read_lock.
  */
 static inline bool console_is_usable(struct console *con)
 {
         short flags = console_srcu_read_flags(con);
 
         if (!(flags & CON_ENABLED))
                 return false;
 
         if ((flags & CON_SUSPENDED))
                 return false;
 
         if (!con->write)
                 return false;
 
         /*
          * Console drivers may assume that per-cpu resources have been
          * allocated. So unless they're explicitly marked as being able to
          * cope (CON_ANYTIME) don't call them until this CPU is officially up.
          */
         if (!cpu_online(raw_smp_processor_id()) && !(flags & CON_ANYTIME))
                 return false;
 
         return true;
 }
 
 static void __console_unlock(void)
 {
         console_locked = 0;
         up_console_sem();
 }
 
 #ifdef CONFIG_PRINTK
 
 /*
  * Prepend the message in @pmsg->pbufs->outbuf with a "dropped message". This
  * is achieved by shifting the existing message over and inserting the dropped
  * message.
  *
  * @pmsg is the printk message to prepend.
  *
  * @dropped is the dropped count to report in the dropped message.
  *
  * If the message text in @pmsg->pbufs->outbuf does not have enough space for
  * the dropped message, the message text will be sufficiently truncated.
  *
  * If @pmsg->pbufs->outbuf is modified, @pmsg->outbuf_len is updated.
  */
 void console_prepend_dropped(struct printk_message *pmsg, unsigned long dropped)
 {
         struct printk_buffers *pbufs = pmsg->pbufs;
         const size_t scratchbuf_sz = sizeof(pbufs->scratchbuf);
         const size_t outbuf_sz = sizeof(pbufs->outbuf);
         char *scratchbuf = &pbufs->scratchbuf[0];
         char *outbuf = &pbufs->outbuf[0];
         size_t len;
 
         len = scnprintf(scratchbuf, scratchbuf_sz,
                        "** %lu printk messages dropped **\n", dropped);
 
         /*
          * Make sure outbuf is sufficiently large before prepending.
          * Keep at least the prefix when the message must be truncated.
          * It is a rather theoretical problem when someone tries to
          * use a minimalist buffer.
          */
         if (WARN_ON_ONCE(len + PRINTK_PREFIX_MAX >= outbuf_sz))
                 return;
 
         if (pmsg->outbuf_len + len >= outbuf_sz) {
                 /* Truncate the message, but keep it terminated. */
                 pmsg->outbuf_len = outbuf_sz - (len + 1);
                 outbuf[pmsg->outbuf_len] = 0;
         }
 
         memmove(outbuf + len, outbuf, pmsg->outbuf_len + 1);
         memcpy(outbuf, scratchbuf, len);
         pmsg->outbuf_len += len;
 }
 
 /*
  * Read and format the specified record (or a later record if the specified
  * record is not available).
  *
  * @pmsg will contain the formatted result. @pmsg->pbufs must point to a
  * struct printk_buffers.
  *
  * @seq is the record to read and format. If it is not available, the next
  * valid record is read.
  *
  * @is_extended specifies if the message should be formatted for extended
  * console output.
  *
  * @may_supress specifies if records may be skipped based on loglevel.
  *
  * Returns false if no record is available. Otherwise true and all fields
  * of @pmsg are valid. (See the documentation of struct printk_message
  * for information about the @pmsg fields.)
  */
 bool printk_get_next_message(struct printk_message *pmsg, u64 seq,
                              bool is_extended, bool may_suppress)
 {
         struct printk_buffers *pbufs = pmsg->pbufs;
         const size_t scratchbuf_sz = sizeof(pbufs->scratchbuf);
         const size_t outbuf_sz = sizeof(pbufs->outbuf);
         char *scratchbuf = &pbufs->scratchbuf[0];
         char *outbuf = &pbufs->outbuf[0];
         struct printk_info info;
         struct printk_record r;
         size_t len = 0;
 
         /*
          * Formatting extended messages requires a separate buffer, so use the
          * scratch buffer to read in the ringbuffer text.
          *
          * Formatting normal messages is done in-place, so read the ringbuffer
          * text directly into the output buffer.
          */
         if (is_extended)
                 prb_rec_init_rd(&r, &info, scratchbuf, scratchbuf_sz);
         else
                 prb_rec_init_rd(&r, &info, outbuf, outbuf_sz);
 
         if (!prb_read_valid(prb, seq, &r))
                 return false;
 
         pmsg->seq = r.info->seq;
         pmsg->dropped = r.info->seq - seq;
 
         /* Skip record that has level above the console loglevel. */
         if (may_suppress && suppress_message_printing(r.info->level))
                 goto out;
 
         if (is_extended) {
                 len = info_print_ext_header(outbuf, outbuf_sz, r.info);
                 len += msg_print_ext_body(outbuf + len, outbuf_sz - len,
                                           &r.text_buf[0], r.info->text_len, &r.info->dev_info);
         } else {
                 len = record_print_text(&r, console_msg_format & MSG_FORMAT_SYSLOG, printk_time);
         }
 out:
         pmsg->outbuf_len = len;
         return true;
 }
 
 /*
  * Used as the printk buffers for non-panic, serialized console printing.
  * This is for legacy (!CON_NBCON) as well as all boot (CON_BOOT) consoles.
  * Its usage requires the console_lock held.
  */
 struct printk_buffers printk_shared_pbufs;
 
 /*
  * Print one record for the given console. The record printed is whatever
  * record is the next available record for the given console.
  *
  * @handover will be set to true if a printk waiter has taken over the
  * console_lock, in which case the caller is no longer holding both the
  * console_lock and the SRCU read lock. Otherwise it is set to false.
  *
  * @cookie is the cookie from the SRCU read lock.
  *
  * Returns false if the given console has no next record to print, otherwise
  * true.
  *
  * Requires the console_lock and the SRCU read lock.
  */
 static bool console_emit_next_record(struct console *con, bool *handover, int cookie)
 {
         bool is_extended = console_srcu_read_flags(con) & CON_EXTENDED;
         char *outbuf = &printk_shared_pbufs.outbuf[0];
         struct printk_message pmsg = {
                 .pbufs = &printk_shared_pbufs,
         };
         unsigned long flags;
 
         *handover = false;
 
         if (!printk_get_next_message(&pmsg, con->seq, is_extended, true))
                 return false;
 
         con->dropped += pmsg.dropped;
 
         /* Skip messages of formatted length 0. */
         if (pmsg.outbuf_len == 0) {
                 con->seq = pmsg.seq + 1;
                 goto skip;
         }
 
         if (con->dropped && !is_extended) {
                 console_prepend_dropped(&pmsg, con->dropped);
                 con->dropped = 0;
         }
 
         /*
          * While actively printing out messages, if another printk()
          * were to occur on another CPU, it may wait for this one to
          * finish. This task can not be preempted if there is a
          * waiter waiting to take over.
          *
          * Interrupts are disabled because the hand over to a waiter
          * must not be interrupted until the hand over is completed
          * (@console_waiter is cleared).
          */
         printk_safe_enter_irqsave(flags);
         console_lock_spinning_enable();
 
         /* Do not trace print latency. */
         stop_critical_timings();
 
         /* Write everything out to the hardware. */
         con->write(con, outbuf, pmsg.outbuf_len);
 
         start_critical_timings();
 
         con->seq = pmsg.seq + 1;
 
         *handover = console_lock_spinning_disable_and_check(cookie);
         printk_safe_exit_irqrestore(flags);
 skip:
         return true;
 }
 
 #else
 
 static bool console_emit_next_record(struct console *con, bool *handover, int cookie)
 {
         *handover = false;
         return false;
 }
 
 #endif /* CONFIG_PRINTK */
 
 /*
  * Print out all remaining records to all consoles.
  *
  * @do_cond_resched is set by the caller. It can be true only in schedulable
  * context.
  *
  * @next_seq is set to the sequence number after the last available record.
  * The value is valid only when this function returns true. It means that all
  * usable consoles are completely flushed.
  *
  * @handover will be set to true if a printk waiter has taken over the
  * console_lock, in which case the caller is no longer holding the
  * console_lock. Otherwise it is set to false.
  *
  * Returns true when there was at least one usable console and all messages
  * were flushed to all usable consoles. A returned false informs the caller
  * that everything was not flushed (either there were no usable consoles or
  * another context has taken over printing or it is a panic situation and this
  * is not the panic CPU). Regardless the reason, the caller should assume it
  * is not useful to immediately try again.
  *
  * Requires the console_lock.
  */
 static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handover)
 {
         bool any_usable = false;
         struct console *con;
         bool any_progress;
         int cookie;
 
         *next_seq = 0;
         *handover = false;
 
         do {
                 any_progress = false;
 
                 cookie = console_srcu_read_lock();
                 for_each_console_srcu(con) {
                         bool progress;
 
                         if (!console_is_usable(con))
                                 continue;
                         any_usable = true;
 
                         progress = console_emit_next_record(con, handover, cookie);
 
                         /*
                          * If a handover has occurred, the SRCU read lock
                          * is already released.
                          */
                         if (*handover)
                                 return false;
 
                         /* Track the next of the highest seq flushed. */
                         if (con->seq > *next_seq)
                                 *next_seq = con->seq;
 
                         if (!progress)
                                 continue;
                         any_progress = true;
 
                         /* Allow panic_cpu to take over the consoles safely. */
                         if (other_cpu_in_panic())
                                 goto abandon;
 
                         if (do_cond_resched)
                                 cond_resched();
                 }
                 console_srcu_read_unlock(cookie);
         } while (any_progress);
 
         return any_usable;
 
 abandon:
         console_srcu_read_unlock(cookie);
         return false;
 }
 
 /**
  * console_unlock - unblock the console subsystem from printing
  *
  * Releases the console_lock which the caller holds to block printing of
  * the console subsystem.
  *
  * While the console_lock was held, console output may have been buffered
  * by printk().  If this is the case, console_unlock(); emits
  * the output prior to releasing the lock.
  *
  * console_unlock(); may be called from any context.
  */
 void console_unlock(void)
 {
         bool do_cond_resched;
         bool handover;
         bool flushed;
         u64 next_seq;
 
         /*
          * Console drivers are called with interrupts disabled, so
          * @console_may_schedule should be cleared before; however, we may
          * end up dumping a lot of lines, for example, if called from
          * console registration path, and should invoke cond_resched()
          * between lines if allowable.  Not doing so can cause a very long
          * scheduling stall on a slow console leading to RCU stall and
          * softlockup warnings which exacerbate the issue with more
          * messages practically incapacitating the system. Therefore, create
          * a local to use for the printing loop.
          */
         do_cond_resched = console_may_schedule;
 
         do {
                 console_may_schedule = 0;
 
                 flushed = console_flush_all(do_cond_resched, &next_seq, &handover);
                 if (!handover)
                         __console_unlock();
 
                 /*
                  * Abort if there was a failure to flush all messages to all
                  * usable consoles. Either it is not possible to flush (in
                  * which case it would be an infinite loop of retrying) or
                  * another context has taken over printing.
                  */
                 if (!flushed)
                         break;
 
                 /*
                  * Some context may have added new records after
                  * console_flush_all() but before unlocking the console.
                  * Re-check if there is a new record to flush. If the trylock
                  * fails, another context is already handling the printing.
                  */
         } while (prb_read_valid(prb, next_seq, NULL) && console_trylock());
 }
 EXPORT_SYMBOL(console_unlock);
 
 /**
  * console_conditional_schedule - yield the CPU if required
  *
  * If the console code is currently allowed to sleep, and
  * if this CPU should yield the CPU to another task, do
  * so here.
  *
  * Must be called within console_lock();.
  */
 void __sched console_conditional_schedule(void)
 {
         if (console_may_schedule)
                 cond_resched();
 }
 EXPORT_SYMBOL(console_conditional_schedule);
 
 void console_unblank(void)
 {
         bool found_unblank = false;
         struct console *c;
         int cookie;
 
         /*
          * First check if there are any consoles implementing the unblank()
          * callback. If not, there is no reason to continue and take the
          * console lock, which in particular can be dangerous if
          * @oops_in_progress is set.
          */
         cookie = console_srcu_read_lock();
         for_each_console_srcu(c) {
                 if ((console_srcu_read_flags(c) & CON_ENABLED) && c->unblank) {
                         found_unblank = true;
                         break;
                 }
         }
         console_srcu_read_unlock(cookie);
         if (!found_unblank)
                 return;
 
         /*
          * Stop console printing because the unblank() callback may
          * assume the console is not within its write() callback.
          *
          * If @oops_in_progress is set, this may be an atomic context.
          * In that case, attempt a trylock as best-effort.
          */
         if (oops_in_progress) {
                 /* Semaphores are not NMI-safe. */
                 if (in_nmi())
                         return;
 
                 /*
                  * Attempting to trylock the console lock can deadlock
                  * if another CPU was stopped while modifying the
                  * semaphore. "Hope and pray" that this is not the
                  * current situation.
                  */
                 if (down_trylock_console_sem() != 0)
                         return;
         } else
                 console_lock();
 
         console_locked = 1;
         console_may_schedule = 0;
 
         cookie = console_srcu_read_lock();
         for_each_console_srcu(c) {
                 if ((console_srcu_read_flags(c) & CON_ENABLED) && c->unblank)
                         c->unblank();
         }
         console_srcu_read_unlock(cookie);
 
         console_unlock();
 
         if (!oops_in_progress)
                 pr_flush(1000, true);
 }
 
 /*
  * Rewind all consoles to the oldest available record.
  *
  * IMPORTANT: The function is safe only when called under
  *            console_lock(). It is not enforced because
  *            it is used as a best effort in panic().
  */
 static void __console_rewind_all(void)
 {
         struct console *c;
         short flags;
         int cookie;
         u64 seq;
 
         seq = prb_first_valid_seq(prb);
 
         cookie = console_srcu_read_lock();
         for_each_console_srcu(c) {
                 flags = console_srcu_read_flags(c);
 
                 if (flags & CON_NBCON) {
                         nbcon_seq_force(c, seq);
                 } else {
                         /*
                          * This assignment is safe only when called under
                          * console_lock(). On panic, legacy consoles are
                          * only best effort.
                          */
                         c->seq = seq;
                 }
         }
         console_srcu_read_unlock(cookie);
 }
 
 /**
  * console_flush_on_panic - flush console content on panic
  * @mode: flush all messages in buffer or just the pending ones
  *
  * Immediately output all pending messages no matter what.
  */
 void console_flush_on_panic(enum con_flush_mode mode)
 {
         bool handover;
         u64 next_seq;
 
         /*
          * Ignore the console lock and flush out the messages. Attempting a
          * trylock would not be useful because:
          *
          *   - if it is contended, it must be ignored anyway
          *   - console_lock() and console_trylock() block and fail
          *     respectively in panic for non-panic CPUs
          *   - semaphores are not NMI-safe
          */
 
         /*
          * If another context is holding the console lock,
          * @console_may_schedule might be set. Clear it so that
          * this context does not call cond_resched() while flushing.
          */
         console_may_schedule = 0;
 
         if (mode == CONSOLE_REPLAY_ALL)
                 __console_rewind_all();
 
         console_flush_all(false, &next_seq, &handover);
 }
 
 /*
  * Return the console tty driver structure and its associated index
  */
 struct tty_driver *console_device(int *index)
 {
         struct console *c;
         struct tty_driver *driver = NULL;
         int cookie;
 
         /*
          * Take console_lock to serialize device() callback with
          * other console operations. For example, fg_console is
          * modified under console_lock when switching vt.
          */
         console_lock();
 
         cookie = console_srcu_read_lock();
         for_each_console_srcu(c) {
                 if (!c->device)
                         continue;
                 driver = c->device(c, index);
                 if (driver)
                         break;
         }
         console_srcu_read_unlock(cookie);
 
         console_unlock();
         return driver;
 }
 
 /*
  * Prevent further output on the passed console device so that (for example)
  * serial drivers can disable console output before suspending a port, and can
  * re-enable output afterwards.
  */
 void console_stop(struct console *console)
 {
         __pr_flush(console, 1000, true);
         console_list_lock();
         console_srcu_write_flags(console, console->flags & ~CON_ENABLED);
         console_list_unlock();
 
         /*
          * Ensure that all SRCU list walks have completed. All contexts must
          * be able to see that this console is disabled so that (for example)
          * the caller can suspend the port without risk of another context
          * using the port.
          */
         synchronize_srcu(&console_srcu);
 }
 EXPORT_SYMBOL(console_stop);
 
 void console_start(struct console *console)
 {
         console_list_lock();
         console_srcu_write_flags(console, console->flags | CON_ENABLED);
         console_list_unlock();
         __pr_flush(console, 1000, true);
 }
 EXPORT_SYMBOL(console_start);
 
 static int __read_mostly keep_bootcon;
 
 static int __init keep_bootcon_setup(char *str)
 {
         keep_bootcon = 1;
         pr_info("debug: skip boot console de-registration.\n");
 
         return 0;
 }
 
 early_param("keep_bootcon", keep_bootcon_setup);
 
 static int console_call_setup(struct console *newcon, char *options)
 {
         int err;
 
         if (!newcon->setup)
                 return 0;
 
         /* Synchronize with possible boot console. */
         console_lock();
         err = newcon->setup(newcon, options);
         console_unlock();
 
         return err;
 }
 
 /*
  * This is called by register_console() to try to match
  * the newly registered console with any of the ones selected
  * by either the command line or add_preferred_console() and
  * setup/enable it.
  *
  * Care need to be taken with consoles that are statically
  * enabled such as netconsole
  */
 static int try_enable_preferred_console(struct console *newcon,
                                         bool user_specified)
 {
         struct console_cmdline *c;
         int i, err;
 
         for (i = 0, c = console_cmdline;
              i < MAX_CMDLINECONSOLES && (c->name[0] || c->devname[0]);
              i++, c++) {
                 /* Console not yet initialized? */
                 if (!c->name[0])
                         continue;
                 if (c->user_specified != user_specified)
                         continue;
                 if (!newcon->match ||
                     newcon->match(newcon, c->name, c->index, c->options) != 0) {
                         /* default matching */
                         BUILD_BUG_ON(sizeof(c->name) != sizeof(newcon->name));
                         if (strcmp(c->name, newcon->name) != 0)
                                 continue;
                         if (newcon->index >= 0 &&
                             newcon->index != c->index)
                                 continue;
                         if (newcon->index < 0)
                                 newcon->index = c->index;
 
                         if (_braille_register_console(newcon, c))
                                 return 0;
 
                         err = console_call_setup(newcon, c->options);
                         if (err)
                                 return err;
                 }
                 newcon->flags |= CON_ENABLED;
                 if (i == preferred_console)
                         newcon->flags |= CON_CONSDEV;
                 return 0;
         }
 
         /*
          * Some consoles, such as pstore and netconsole, can be enabled even
          * without matching. Accept the pre-enabled consoles only when match()
          * and setup() had a chance to be called.
          */
         if (newcon->flags & CON_ENABLED && c->user_specified == user_specified)
                 return 0;
 
         return -ENOENT;
 }
 
 /* Try to enable the console unconditionally */
 static void try_enable_default_console(struct console *newcon)
 {
         if (newcon->index < 0)
                 newcon->index = 0;
 
         if (console_call_setup(newcon, NULL) != 0)
                 return;
 
         newcon->flags |= CON_ENABLED;
 
         if (newcon->device)
                 newcon->flags |= CON_CONSDEV;
 }
 
 static void console_init_seq(struct console *newcon, bool bootcon_registered)
 {
         struct console *con;
         bool handover;
 
         if (newcon->flags & (CON_PRINTBUFFER | CON_BOOT)) {
                 /* Get a consistent copy of @syslog_seq. */
                 mutex_lock(&syslog_lock);
                 newcon->seq = syslog_seq;
                 mutex_unlock(&syslog_lock);
         } else {
                 /* Begin with next message added to ringbuffer. */
                 newcon->seq = prb_next_seq(prb);
 
                 /*
                  * If any enabled boot consoles are due to be unregistered
                  * shortly, some may not be caught up and may be the same
                  * device as @newcon. Since it is not known which boot console
                  * is the same device, flush all consoles and, if necessary,
                  * start with the message of the enabled boot console that is
                  * the furthest behind.
                  */
                 if (bootcon_registered && !keep_bootcon) {
                         /*
                          * Hold the console_lock to stop console printing and
                          * guarantee safe access to console->seq.
                          */
                         console_lock();
 
                         /*
                          * Flush all consoles and set the console to start at
                          * the next unprinted sequence number.
                          */
                         if (!console_flush_all(true, &newcon->seq, &handover)) {
                                 /*
                                  * Flushing failed. Just choose the lowest
                                  * sequence of the enabled boot consoles.
                                  */
 
                                 /*
                                  * If there was a handover, this context no
                                  * longer holds the console_lock.
                                  */
                                 if (handover)
                                         console_lock();
 
                                 newcon->seq = prb_next_seq(prb);
                                 for_each_console(con) {
                                         if ((con->flags & CON_BOOT) &&
                                             (con->flags & CON_ENABLED) &&
                                             con->seq < newcon->seq) {
                                                 newcon->seq = con->seq;
                                         }
                                 }
                         }
 
                         console_unlock();
                 }
         }
 }
 
 #define console_first()                         \
         hlist_entry(console_list.first, struct console, node)
 
 static int unregister_console_locked(struct console *console);
 
 /*
  * The console driver calls this routine during kernel initialization
  * to register the console printing procedure with printk() and to
  * print any messages that were printed by the kernel before the
  * console driver was initialized.
  *
  * This can happen pretty early during the boot process (because of
  * early_printk) - sometimes before setup_arch() completes - be careful
  * of what kernel features are used - they may not be initialised yet.
  *
  * There are two types of consoles - bootconsoles (early_printk) and
  * "real" consoles (everything which is not a bootconsole) which are
  * handled differently.
  *  - Any number of bootconsoles can be registered at any time.
  *  - As soon as a "real" console is registered, all bootconsoles
  *    will be unregistered automatically.
  *  - Once a "real" console is registered, any attempt to register a
  *    bootconsoles will be rejected
  */
 void register_console(struct console *newcon)
 {
         struct console *con;
         bool bootcon_registered = false;
         bool realcon_registered = false;
         int err;
 
         console_list_lock();
 
         for_each_console(con) {
                 if (WARN(con == newcon, "console '%s%d' already registered\n",
                                          con->name, con->index)) {
                         goto unlock;
                 }
 
                 if (con->flags & CON_BOOT)
                         bootcon_registered = true;
                 else
                         realcon_registered = true;
         }
 
         /* Do not register boot consoles when there already is a real one. */
         if ((newcon->flags & CON_BOOT) && realcon_registered) {
                 pr_info("Too late to register bootconsole %s%d\n",
                         newcon->name, newcon->index);
                 goto unlock;
         }
 
         if (newcon->flags & CON_NBCON) {
                 /*
                  * Ensure the nbcon console buffers can be allocated
                  * before modifying any global data.
                  */
                 if (!nbcon_alloc(newcon))
                         goto unlock;
         }
 
         /*
          * See if we want to enable this console driver by default.
          *
          * Nope when a console is preferred by the command line, device
          * tree, or SPCR.
          *
          * The first real console with tty binding (driver) wins. More
          * consoles might get enabled before the right one is found.
          *
          * Note that a console with tty binding will have CON_CONSDEV
          * flag set and will be first in the list.
          */
         if (preferred_console < 0) {
                 if (hlist_empty(&console_list) || !console_first()->device ||
                     console_first()->flags & CON_BOOT) {
                         try_enable_default_console(newcon);
                 }
         }
 
         /* See if this console matches one we selected on the command line */
         err = try_enable_preferred_console(newcon, true);
 
         /* If not, try to match against the platform default(s) */
         if (err == -ENOENT)
                 err = try_enable_preferred_console(newcon, false);
 
         /* printk() messages are not printed to the Braille console. */
         if (err || newcon->flags & CON_BRL) {
                 if (newcon->flags & CON_NBCON)
                         nbcon_free(newcon);
                 goto unlock;
         }
 
         /*
          * If we have a bootconsole, and are switching to a real console,
          * don't print everything out again, since when the boot console, and
          * the real console are the same physical device, it's annoying to
          * see the beginning boot messages twice
          */
         if (bootcon_registered &&
             ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV)) {
                 newcon->flags &= ~CON_PRINTBUFFER;
         }
 
         newcon->dropped = 0;
         console_init_seq(newcon, bootcon_registered);
 
         if (newcon->flags & CON_NBCON)
                 nbcon_init(newcon);
 
         /*
          * Put this console in the list - keep the
          * preferred driver at the head of the list.
          */
         if (hlist_empty(&console_list)) {
                 /* Ensure CON_CONSDEV is always set for the head. */
                 newcon->flags |= CON_CONSDEV;
                 hlist_add_head_rcu(&newcon->node, &console_list);
 
         } else if (newcon->flags & CON_CONSDEV) {
                 /* Only the new head can have CON_CONSDEV set. */
                 console_srcu_write_flags(console_first(), console_first()->flags & ~CON_CONSDEV);
                 hlist_add_head_rcu(&newcon->node, &console_list);
 
         } else {
                 hlist_add_behind_rcu(&newcon->node, console_list.first);
         }
 
         /*
          * No need to synchronize SRCU here! The caller does not rely
          * on all contexts being able to see the new console before
          * register_console() completes.
          */
 
         console_sysfs_notify();
 
         /*
          * By unregistering the bootconsoles after we enable the real console
          * we get the "console xxx enabled" message on all the consoles -
          * boot consoles, real consoles, etc - this is to ensure that end
          * users know there might be something in the kernel's log buffer that
          * went to the bootconsole (that they do not see on the real console)
          */
         con_printk(KERN_INFO, newcon, "enabled\n");
         if (bootcon_registered &&
             ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV) &&
             !keep_bootcon) {
                 struct hlist_node *tmp;
 
                 hlist_for_each_entry_safe(con, tmp, &console_list, node) {
                         if (con->flags & CON_BOOT)
                                 unregister_console_locked(con);
                 }
         }
 unlock:
         console_list_unlock();
 }
 EXPORT_SYMBOL(register_console);
 
 /* Must be called under console_list_lock(). */
 static int unregister_console_locked(struct console *console)
 {
         int res;
 
         lockdep_assert_console_list_lock_held();
 
         con_printk(KERN_INFO, console, "disabled\n");
 
         res = _braille_unregister_console(console);
         if (res < 0)
                 return res;
         if (res > 0)
                 return 0;
 
         /* Disable it unconditionally */
         console_srcu_write_flags(console, console->flags & ~CON_ENABLED);
 
         if (!console_is_registered_locked(console))
                 return -ENODEV;
 
         hlist_del_init_rcu(&console->node);
 
         /*
          * <HISTORICAL>
          * If this isn't the last console and it has CON_CONSDEV set, we
          * need to set it on the next preferred console.
          * </HISTORICAL>
          *
          * The above makes no sense as there is no guarantee that the next
          * console has any device attached. Oh well....
          */
         if (!hlist_empty(&console_list) && console->flags & CON_CONSDEV)
                 console_srcu_write_flags(console_first(), console_first()->flags | CON_CONSDEV);
 
         /*
          * Ensure that all SRCU list walks have completed. All contexts
          * must not be able to see this console in the list so that any
          * exit/cleanup routines can be performed safely.
          */
         synchronize_srcu(&console_srcu);
 
         if (console->flags & CON_NBCON)
                 nbcon_free(console);
 
         console_sysfs_notify();
 
         if (console->exit)
                 res = console->exit(console);
 
         return res;
 }
 
 int unregister_console(struct console *console)
 {
         int res;
 
         console_list_lock();
         res = unregister_console_locked(console);
         console_list_unlock();
         return res;
 }
 EXPORT_SYMBOL(unregister_console);
 
 /**
  * console_force_preferred_locked - force a registered console preferred
  * @con: The registered console to force preferred.
  *
  * Must be called under console_list_lock().
  */
 void console_force_preferred_locked(struct console *con)
 {
         struct console *cur_pref_con;
 
         if (!console_is_registered_locked(con))
                 return;
 
         cur_pref_con = console_first();
 
         /* Already preferred? */
         if (cur_pref_con == con)
                 return;
 
         /*
          * Delete, but do not re-initialize the entry. This allows the console
          * to continue to appear registered (via any hlist_unhashed_lockless()
          * checks), even though it was briefly removed from the console list.
          */
         hlist_del_rcu(&con->node);
 
         /*
          * Ensure that all SRCU list walks have completed so that the console
          * can be added to the beginning of the console list and its forward
          * list pointer can be re-initialized.
          */
         synchronize_srcu(&console_srcu);
 
         con->flags |= CON_CONSDEV;
         WARN_ON(!con->device);
 
         /* Only the new head can have CON_CONSDEV set. */
         console_srcu_write_flags(cur_pref_con, cur_pref_con->flags & ~CON_CONSDEV);
         hlist_add_head_rcu(&con->node, &console_list);
 }
 EXPORT_SYMBOL(console_force_preferred_locked);
 
 /*
  * Initialize the console device. This is called *early*, so
  * we can't necessarily depend on lots of kernel help here.
  * Just do some early initializations, and do the complex setup
  * later.
  */
 void __init console_init(void)
 {
         int ret;
         initcall_t call;
         initcall_entry_t *ce;
 
         /* Setup the default TTY line discipline. */
         n_tty_init();
 
         /*
          * set up the console device so that later boot sequences can
          * inform about problems etc..
          */
         ce = __con_initcall_start;
         trace_initcall_level("console");
         while (ce < __con_initcall_end) {
                 call = initcall_from_entry(ce);
                 trace_initcall_start(call);
                 ret = call();
                 trace_initcall_finish(call, ret);
                 ce++;
         }
 }
 
 /*
  * Some boot consoles access data that is in the init section and which will
  * be discarded after the initcalls have been run. To make sure that no code
  * will access this data, unregister the boot consoles in a late initcall.
  *
  * If for some reason, such as deferred probe or the driver being a loadable
  * module, the real console hasn't registered yet at this point, there will
  * be a brief interval in which no messages are logged to the console, which
  * makes it difficult to diagnose problems that occur during this time.
  *
  * To mitigate this problem somewhat, only unregister consoles whose memory
  * intersects with the init section. Note that all other boot consoles will
  * get unregistered when the real preferred console is registered.
  */
 static int __init printk_late_init(void)
 {
         struct hlist_node *tmp;
         struct console *con;
         int ret;
 
         console_list_lock();
         hlist_for_each_entry_safe(con, tmp, &console_list, node) {
                 if (!(con->flags & CON_BOOT))
                         continue;
 
                 /* Check addresses that might be used for enabled consoles. */
                 if (init_section_intersects(con, sizeof(*con)) ||
                     init_section_contains(con->write, 0) ||
                     init_section_contains(con->read, 0) ||
                     init_section_contains(con->device, 0) ||
                     init_section_contains(con->unblank, 0) ||
                     init_section_contains(con->data, 0)) {
                         /*
                          * Please, consider moving the reported consoles out
                          * of the init section.
                          */
                         pr_warn("bootconsole [%s%d] uses init memory and must be disabled even before the real one is ready\n",
                                 con->name, con->index);
                         unregister_console_locked(con);
                 }
         }
         console_list_unlock();
 
         ret = cpuhp_setup_state_nocalls(CPUHP_PRINTK_DEAD, "printk:dead", NULL,
                                         console_cpu_notify);
         WARN_ON(ret < 0);
         ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "printk:online",
                                         console_cpu_notify, NULL);
         WARN_ON(ret < 0);
         printk_sysctl_init();
         return 0;
 }
 late_initcall(printk_late_init);
 
 #if defined CONFIG_PRINTK
 /* If @con is specified, only wait for that console. Otherwise wait for all. */
 static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress)
 {
         unsigned long timeout_jiffies = msecs_to_jiffies(timeout_ms);
         unsigned long remaining_jiffies = timeout_jiffies;
         struct console *c;
         u64 last_diff = 0;
         u64 printk_seq;
         short flags;
         int cookie;
         u64 diff;
         u64 seq;
 
         might_sleep();
 
         seq = prb_next_reserve_seq(prb);
 
         /* Flush the consoles so that records up to @seq are printed. */
         console_lock();
         console_unlock();
 
         for (;;) {
                 unsigned long begin_jiffies;
                 unsigned long slept_jiffies;
 
                 diff = 0;
 
                 /*
                  * Hold the console_lock to guarantee safe access to
                  * console->seq. Releasing console_lock flushes more
                  * records in case @seq is still not printed on all
                  * usable consoles.
                  */
                 console_lock();
 
                 cookie = console_srcu_read_lock();
                 for_each_console_srcu(c) {
                         if (con && con != c)
                                 continue;
 
                         flags = console_srcu_read_flags(c);
 
                         /*
                          * If consoles are not usable, it cannot be expected
                          * that they make forward progress, so only increment
                          * @diff for usable consoles.
                          */
                         if (!console_is_usable(c))
                                 continue;
 
                         if (flags & CON_NBCON) {
                                 printk_seq = nbcon_seq_read(c);
                         } else {
                                 printk_seq = c->seq;
                         }
 
                         if (printk_seq < seq)
                                 diff += seq - printk_seq;
                 }
                 console_srcu_read_unlock(cookie);
 
                 if (diff != last_diff && reset_on_progress)
                         remaining_jiffies = timeout_jiffies;
 
                 console_unlock();
 
                 /* Note: @diff is 0 if there are no usable consoles. */
                 if (diff == 0 || remaining_jiffies == 0)
                         break;
 
                 /* msleep(1) might sleep much longer. Check time by jiffies. */
                 begin_jiffies = jiffies;
                 msleep(1);
                 slept_jiffies = jiffies - begin_jiffies;
 
                 remaining_jiffies -= min(slept_jiffies, remaining_jiffies);
 
                 last_diff = diff;
         }
 
         return (diff == 0);
 }
 
 /**
  * pr_flush() - Wait for printing threads to catch up.
  *
  * @timeout_ms:        The maximum time (in ms) to wait.
  * @reset_on_progress: Reset the timeout if forward progress is seen.
  *
  * A value of 0 for @timeout_ms means no waiting will occur. A value of -1
  * represents infinite waiting.
  *
  * If @reset_on_progress is true, the timeout will be reset whenever any
  * printer has been seen to make some forward progress.
  *
  * Context: Process context. May sleep while acquiring console lock.
  * Return: true if all usable printers are caught up.
  */
 static bool pr_flush(int timeout_ms, bool reset_on_progress)
 {
         return __pr_flush(NULL, timeout_ms, reset_on_progress);
 }
 
 /*
  * Delayed printk version, for scheduler-internal messages:
  */
 #define PRINTK_PENDING_WAKEUP   0x01
 #define PRINTK_PENDING_OUTPUT   0x02
 
 static DEFINE_PER_CPU(int, printk_pending);
 
 static void wake_up_klogd_work_func(struct irq_work *irq_work)
 {
         int pending = this_cpu_xchg(printk_pending, 0);
 
         if (pending & PRINTK_PENDING_OUTPUT) {
                 /* If trylock fails, someone else is doing the printing */
                 if (console_trylock())
                         console_unlock();
         }
 
         if (pending & PRINTK_PENDING_WAKEUP)
                 wake_up_interruptible(&log_wait);
 }
 
 static DEFINE_PER_CPU(struct irq_work, wake_up_klogd_work) =
         IRQ_WORK_INIT_LAZY(wake_up_klogd_work_func);
 
 static void __wake_up_klogd(int val)
 {
         if (!printk_percpu_data_ready())
                 return;
 
         preempt_disable();
         /*
          * Guarantee any new records can be seen by tasks preparing to wait
          * before this context checks if the wait queue is empty.
          *
          * The full memory barrier within wq_has_sleeper() pairs with the full
          * memory barrier within set_current_state() of
          * prepare_to_wait_event(), which is called after ___wait_event() adds
          * the waiter but before it has checked the wait condition.
          *
          * This pairs with devkmsg_read:A and syslog_print:A.
          */
         if (wq_has_sleeper(&log_wait) || /* LMM(__wake_up_klogd:A) */
             (val & PRINTK_PENDING_OUTPUT)) {
                 this_cpu_or(printk_pending, val);
                 irq_work_queue(this_cpu_ptr(&wake_up_klogd_work));
         }
         preempt_enable();
 }
 
 /**
  * wake_up_klogd - Wake kernel logging daemon
  *
  * Use this function when new records have been added to the ringbuffer
  * and the console printing of those records has already occurred or is
  * known to be handled by some other context. This function will only
  * wake the logging daemon.
  *
  * Context: Any context.
  */
 void wake_up_klogd(void)
 {
         __wake_up_klogd(PRINTK_PENDING_WAKEUP);
 }
 
 /**
  * defer_console_output - Wake kernel logging daemon and trigger
  *      console printing in a deferred context
  *
  * Use this function when new records have been added to the ringbuffer,
  * this context is responsible for console printing those records, but
  * the current context is not allowed to perform the console printing.
  * Trigger an irq_work context to perform the console printing. This
  * function also wakes the logging daemon.
  *
  * Context: Any context.
  */
 void defer_console_output(void)
 {
         /*
          * New messages may have been added directly to the ringbuffer
          * using vprintk_store(), so wake any waiters as well.
          */
         __wake_up_klogd(PRINTK_PENDING_WAKEUP | PRINTK_PENDING_OUTPUT);
 }
 
 void printk_trigger_flush(void)
 {
         defer_console_output();
 }
 
 int vprintk_deferred(const char *fmt, va_list args)
 {
         return vprintk_emit(0, LOGLEVEL_SCHED, NULL, fmt, args);
 }
 
 int _printk_deferred(const char *fmt, ...)
 {
         va_list args;
         int r;
 
         va_start(args, fmt);
         r = vprintk_deferred(fmt, args);
         va_end(args);
 
         return r;
 }
 
 /*
  * printk rate limiting, lifted from the networking subsystem.
  *
  * This enforces a rate limit: not more than 10 kernel messages
  * every 5s to make a denial-of-service attack impossible.
  */
 DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);
 
 int __printk_ratelimit(const char *func)
 {
         return ___ratelimit(&printk_ratelimit_state, func);
 }
 EXPORT_SYMBOL(__printk_ratelimit);
 
 /**
  * printk_timed_ratelimit - caller-controlled printk ratelimiting
  * @caller_jiffies: pointer to caller's state
  * @interval_msecs: minimum interval between prints
  *
  * printk_timed_ratelimit() returns true if more than @interval_msecs
  * milliseconds have elapsed since the last time printk_timed_ratelimit()
  * returned true.
  */
 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
                         unsigned int interval_msecs)
 {
         unsigned long elapsed = jiffies - *caller_jiffies;
 
         if (*caller_jiffies && elapsed <= msecs_to_jiffies(interval_msecs))
                 return false;
 
         *caller_jiffies = jiffies;
         return true;
 }
 EXPORT_SYMBOL(printk_timed_ratelimit);
 
 static DEFINE_SPINLOCK(dump_list_lock);
 static LIST_HEAD(dump_list);
 
 /**
  * kmsg_dump_register - register a kernel log dumper.
  * @dumper: pointer to the kmsg_dumper structure
  *
  * Adds a kernel log dumper to the system. The dump callback in the
  * structure will be called when the kernel oopses or panics and must be
  * set. Returns zero on success and %-EINVAL or %-EBUSY otherwise.
  */
 int kmsg_dump_register(struct kmsg_dumper *dumper)
 {
         unsigned long flags;
         int err = -EBUSY;
 
         /* The dump callback needs to be set */
         if (!dumper->dump)
                 return -EINVAL;
 
         spin_lock_irqsave(&dump_list_lock, flags);
         /* Don't allow registering multiple times */
         if (!dumper->registered) {
                 dumper->registered = 1;
                 list_add_tail_rcu(&dumper->list, &dump_list);
                 err = 0;
         }
         spin_unlock_irqrestore(&dump_list_lock, flags);
 
         return err;
 }
 EXPORT_SYMBOL_GPL(kmsg_dump_register);
 
 /**
  * kmsg_dump_unregister - unregister a kmsg dumper.
  * @dumper: pointer to the kmsg_dumper structure
  *
  * Removes a dump device from the system. Returns zero on success and
  * %-EINVAL otherwise.
  */
 int kmsg_dump_unregister(struct kmsg_dumper *dumper)
 {
         unsigned long flags;
         int err = -EINVAL;
 
         spin_lock_irqsave(&dump_list_lock, flags);
         if (dumper->registered) {
                 dumper->registered = 0;
                 list_del_rcu(&dumper->list);
                 err = 0;
         }
         spin_unlock_irqrestore(&dump_list_lock, flags);
         synchronize_rcu();
 
         return err;
 }
 EXPORT_SYMBOL_GPL(kmsg_dump_unregister);
 
 static bool always_kmsg_dump;
 module_param_named(always_kmsg_dump, always_kmsg_dump, bool, S_IRUGO | S_IWUSR);
 
 const char *kmsg_dump_reason_str(enum kmsg_dump_reason reason)
 {
         switch (reason) {
         case KMSG_DUMP_PANIC:
                 return "Panic";
         case KMSG_DUMP_OOPS:
                 return "Oops";
         case KMSG_DUMP_EMERG:
                 return "Emergency";
         case KMSG_DUMP_SHUTDOWN:
                 return "Shutdown";
         default:
                 return "Unknown";
         }
 }
 EXPORT_SYMBOL_GPL(kmsg_dump_reason_str);
 
 /**
  * kmsg_dump - dump kernel log to kernel message dumpers.
  * @reason: the reason (oops, panic etc) for dumping
  *
  * Call each of the registered dumper's dump() callback, which can
  * retrieve the kmsg records with kmsg_dump_get_line() or
  * kmsg_dump_get_buffer().
  */
 void kmsg_dump(enum kmsg_dump_reason reason)
 {
         struct kmsg_dumper *dumper;
 
         rcu_read_lock();
         list_for_each_entry_rcu(dumper, &dump_list, list) {
                 enum kmsg_dump_reason max_reason = dumper->max_reason;
 
                 /*
                  * If client has not provided a specific max_reason, default
                  * to KMSG_DUMP_OOPS, unless always_kmsg_dump was set.
                  */
                 if (max_reason == KMSG_DUMP_UNDEF) {
                         max_reason = always_kmsg_dump ? KMSG_DUMP_MAX :
                                                         KMSG_DUMP_OOPS;
                 }
                 if (reason > max_reason)
                         continue;
 
                 /* invoke dumper which will iterate over records */
                 dumper->dump(dumper, reason);
         }
         rcu_read_unlock();
 }
 
 /**
  * kmsg_dump_get_line - retrieve one kmsg log line
  * @iter: kmsg dump iterator
  * @syslog: include the "<4>" prefixes
  * @line: buffer to copy the line to
  * @size: maximum size of the buffer
  * @len: length of line placed into buffer
  *
  * Start at the beginning of the kmsg buffer, with the oldest kmsg
  * record, and copy one record into the provided buffer.
  *
  * Consecutive calls will return the next available record moving
  * towards the end of the buffer with the youngest messages.
  *
  * A return value of FALSE indicates that there are no more records to
  * read.
  */
 bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
                         char *line, size_t size, size_t *len)
 {
         u64 min_seq = latched_seq_read_nolock(&clear_seq);
         struct printk_info info;
         unsigned int line_count;
         struct printk_record r;
         size_t l = 0;
         bool ret = false;
 
         if (iter->cur_seq < min_seq)
                 iter->cur_seq = min_seq;
 
         prb_rec_init_rd(&r, &info, line, size);
 
         /* Read text or count text lines? */
         if (line) {
                 if (!prb_read_valid(prb, iter->cur_seq, &r))
                         goto out;
                 l = record_print_text(&r, syslog, printk_time);
         } else {
                 if (!prb_read_valid_info(prb, iter->cur_seq,
                                          &info, &line_count)) {
                         goto out;
                 }
                 l = get_record_print_text_size(&info, line_count, syslog,
                                                printk_time);
 
         }
 
         iter->cur_seq = r.info->seq + 1;
         ret = true;
 out:
         if (len)
                 *len = l;
         return ret;
 }
 EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
 
 /**
  * kmsg_dump_get_buffer - copy kmsg log lines
  * @iter: kmsg dump iterator
  * @syslog: include the "<4>" prefixes
  * @buf: buffer to copy the line to
  * @size: maximum size of the buffer
  * @len_out: length of line placed into buffer
  *
  * Start at the end of the kmsg buffer and fill the provided buffer
  * with as many of the *youngest* kmsg records that fit into it.
  * If the buffer is large enough, all available kmsg records will be
  * copied with a single call.
  *
  * Consecutive calls will fill the buffer with the next block of
  * available older records, not including the earlier retrieved ones.
  *
  * A return value of FALSE indicates that there are no more records to
  * read.
  */
 bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
                           char *buf, size_t size, size_t *len_out)
 {
         u64 min_seq = latched_seq_read_nolock(&clear_seq);
         struct printk_info info;
         struct printk_record r;
         u64 seq;
         u64 next_seq;
         size_t len = 0;
         bool ret = false;
         bool time = printk_time;
 
         if (!buf || !size)
                 goto out;
 
         if (iter->cur_seq < min_seq)
                 iter->cur_seq = min_seq;
 
         if (prb_read_valid_info(prb, iter->cur_seq, &info, NULL)) {
                 if (info.seq != iter->cur_seq) {
                         /* messages are gone, move to first available one */
                         iter->cur_seq = info.seq;
                 }
         }
 
         /* last entry */
         if (iter->cur_seq >= iter->next_seq)
                 goto out;
 
         /*
          * Find first record that fits, including all following records,
          * into the user-provided buffer for this dump. Pass in size-1
          * because this function (by way of record_print_text()) will
          * not write more than size-1 bytes of text into @buf.
          */
         seq = find_first_fitting_seq(iter->cur_seq, iter->next_seq,
                                      size - 1, syslog, time);
 
         /*
          * Next kmsg_dump_get_buffer() invocation will dump block of
          * older records stored right before this one.
          */
         next_seq = seq;
 
         prb_rec_init_rd(&r, &info, buf, size);
 
         prb_for_each_record(seq, prb, seq, &r) {
                 if (r.info->seq >= iter->next_seq)
                         break;
 
                 len += record_print_text(&r, syslog, time);
 
                 /* Adjust record to store to remaining buffer space. */
                 prb_rec_init_rd(&r, &info, buf + len, size - len);
         }
 
         iter->next_seq = next_seq;
         ret = true;
 out:
         if (len_out)
                 *len_out = len;
         return ret;
 }
 EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
 
 /**
  * kmsg_dump_rewind - reset the iterator
  * @iter: kmsg dump iterator
  *
  * Reset the dumper's iterator so that kmsg_dump_get_line() and
  * kmsg_dump_get_buffer() can be called again and used multiple
  * times within the same dumper.dump() callback.
  */
 void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
 {
         iter->cur_seq = latched_seq_read_nolock(&clear_seq);
         iter->next_seq = prb_next_seq(prb);
 }
 EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
 
 /**
  * console_try_replay_all - try to replay kernel log on consoles
  *
  * Try to obtain lock on console subsystem and replay all
  * available records in printk buffer on the consoles.
  * Does nothing if lock is not obtained.
  *
  * Context: Any, except for NMI.
  */
 void console_try_replay_all(void)
 {
         if (console_trylock()) {
                 __console_rewind_all();
                 /* Consoles are flushed as part of console_unlock(). */
                 console_unlock();
         }
 }
 #endif
 
 #ifdef CONFIG_SMP
 static atomic_t printk_cpu_sync_owner = ATOMIC_INIT(-1);
 static atomic_t printk_cpu_sync_nested = ATOMIC_INIT(0);
 
 /**
  * __printk_cpu_sync_wait() - Busy wait until the printk cpu-reentrant
  *                            spinning lock is not owned by any CPU.
  *
  * Context: Any context.
  */
 void __printk_cpu_sync_wait(void)
 {
         do {
                 cpu_relax();
         } while (atomic_read(&printk_cpu_sync_owner) != -1);
 }
 EXPORT_SYMBOL(__printk_cpu_sync_wait);
 
 /**
  * __printk_cpu_sync_try_get() - Try to acquire the printk cpu-reentrant
  *                               spinning lock.
  *
  * If no processor has the lock, the calling processor takes the lock and
  * becomes the owner. If the calling processor is already the owner of the
  * lock, this function succeeds immediately.
  *
  * Context: Any context. Expects interrupts to be disabled.
  * Return: 1 on success, otherwise 0.
  */
 int __printk_cpu_sync_try_get(void)
 {
         int cpu;
         int old;
 
         cpu = smp_processor_id();
 
         /*
          * Guarantee loads and stores from this CPU when it is the lock owner
          * are _not_ visible to the previous lock owner. This pairs with
          * __printk_cpu_sync_put:B.
          *
          * Memory barrier involvement:
          *
          * If __printk_cpu_sync_try_get:A reads from __printk_cpu_sync_put:B,
          * then __printk_cpu_sync_put:A can never read from
          * __printk_cpu_sync_try_get:B.
          *
          * Relies on:
          *
          * RELEASE from __printk_cpu_sync_put:A to __printk_cpu_sync_put:B
          * of the previous CPU
          *    matching
          * ACQUIRE from __printk_cpu_sync_try_get:A to
          * __printk_cpu_sync_try_get:B of this CPU
          */
         old = atomic_cmpxchg_acquire(&printk_cpu_sync_owner, -1,
                                      cpu); /* LMM(__printk_cpu_sync_try_get:A) */
         if (old == -1) {
                 /*
                  * This CPU is now the owner and begins loading/storing
                  * data: LMM(__printk_cpu_sync_try_get:B)
                  */
                 return 1;
 
         } else if (old == cpu) {
                 /* This CPU is already the owner. */
                 atomic_inc(&printk_cpu_sync_nested);
                 return 1;
         }
 
         return 0;
 }
 EXPORT_SYMBOL(__printk_cpu_sync_try_get);
 
 /**
  * __printk_cpu_sync_put() - Release the printk cpu-reentrant spinning lock.
  *
  * The calling processor must be the owner of the lock.
  *
  * Context: Any context. Expects interrupts to be disabled.
  */
 void __printk_cpu_sync_put(void)
 {
         if (atomic_read(&printk_cpu_sync_nested)) {
                 atomic_dec(&printk_cpu_sync_nested);
                 return;
         }
 
         /*
          * This CPU is finished loading/storing data:
          * LMM(__printk_cpu_sync_put:A)
          */
 
         /*
          * Guarantee loads and stores from this CPU when it was the
          * lock owner are visible to the next lock owner. This pairs
          * with __printk_cpu_sync_try_get:A.
          *
          * Memory barrier involvement:
          *
          * If __printk_cpu_sync_try_get:A reads from __printk_cpu_sync_put:B,
          * then __printk_cpu_sync_try_get:B reads from __printk_cpu_sync_put:A.
          *
          * Relies on:
          *
          * RELEASE from __printk_cpu_sync_put:A to __printk_cpu_sync_put:B
          * of this CPU
          *    matching
          * ACQUIRE from __printk_cpu_sync_try_get:A to
          * __printk_cpu_sync_try_get:B of the next CPU
          */
         atomic_set_release(&printk_cpu_sync_owner,
                            -1); /* LMM(__printk_cpu_sync_put:B) */
 }
 EXPORT_SYMBOL(__printk_cpu_sync_put);
 #endif /* CONFIG_SMP */