1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Copyright (C) 2008 Oracle. All rights reserved.
4 */
5
6 #include <linux/sched.h>
7 #include <linux/pagemap.h>
8 #include <linux/spinlock.h>
9 #include <linux/page-flags.h>
10 #include <asm/bug.h>
11 #include <trace/events/btrfs.h>
12 #include "misc.h"
13 #include "ctree.h"
14 #include "extent_io.h"
15 #include "locking.h"
16
17 /*
18 * Lockdep class keys for extent_buffer->lock's in this root. For a given
19 * eb, the lockdep key is determined by the btrfs_root it belongs to and
20 * the level the eb occupies in the tree.
21 *
22 * Different roots are used for different purposes and may nest inside each
23 * other and they require separate keysets. As lockdep keys should be
24 * static, assign keysets according to the purpose of the root as indicated
25 * by btrfs_root->root_key.objectid. This ensures that all special purpose
26 * roots have separate keysets.
27 *
28 * Lock-nesting across peer nodes is always done with the immediate parent
29 * node locked thus preventing deadlock. As lockdep doesn't know this, use
30 * subclass to avoid triggering lockdep warning in such cases.
31 *
32 * The key is set by the readpage_end_io_hook after the buffer has passed
33 * csum validation but before the pages are unlocked. It is also set by
34 * btrfs_init_new_buffer on freshly allocated blocks.
35 *
36 * We also add a check to make sure the highest level of the tree is the
37 * same as our lockdep setup here. If BTRFS_MAX_LEVEL changes, this code
38 * needs update as well.
39 */
40 #ifdef CONFIG_DEBUG_LOCK_ALLOC
41 #if BTRFS_MAX_LEVEL != 8
42 #error
43 #endif
44
45 #define DEFINE_LEVEL(stem, level) \
46 .names[level] = "btrfs-" stem "-0" #level,
47
48 #define DEFINE_NAME(stem) \
49 DEFINE_LEVEL(stem, 0) \
50 DEFINE_LEVEL(stem, 1) \
51 DEFINE_LEVEL(stem, 2) \
52 DEFINE_LEVEL(stem, 3) \
53 DEFINE_LEVEL(stem, 4) \
54 DEFINE_LEVEL(stem, 5) \
55 DEFINE_LEVEL(stem, 6) \
56 DEFINE_LEVEL(stem, 7)
57
58 static struct btrfs_lockdep_keyset {
59 u64 id; /* root objectid */
60 /* Longest entry: btrfs-block-group-00 */
61 char names[BTRFS_MAX_LEVEL][24];
62 struct lock_class_key keys[BTRFS_MAX_LEVEL];
63 } btrfs_lockdep_keysets[] = {
64 { .id = BTRFS_ROOT_TREE_OBJECTID, DEFINE_NAME("root") },
65 { .id = BTRFS_EXTENT_TREE_OBJECTID, DEFINE_NAME("extent") },
66 { .id = BTRFS_CHUNK_TREE_OBJECTID, DEFINE_NAME("chunk") },
67 { .id = BTRFS_DEV_TREE_OBJECTID, DEFINE_NAME("dev") },
68 { .id = BTRFS_CSUM_TREE_OBJECTID, DEFINE_NAME("csum") },
69 { .id = BTRFS_QUOTA_TREE_OBJECTID, DEFINE_NAME("quota") },
70 { .id = BTRFS_TREE_LOG_OBJECTID, DEFINE_NAME("log") },
71 { .id = BTRFS_TREE_RELOC_OBJECTID, DEFINE_NAME("treloc") },
72 { .id = BTRFS_DATA_RELOC_TREE_OBJECTID, DEFINE_NAME("dreloc") },
73 { .id = BTRFS_UUID_TREE_OBJECTID, DEFINE_NAME("uuid") },
74 { .id = BTRFS_FREE_SPACE_TREE_OBJECTID, DEFINE_NAME("free-space") },
75 { .id = BTRFS_BLOCK_GROUP_TREE_OBJECTID, DEFINE_NAME("block-group") },
76 { .id = BTRFS_RAID_STRIPE_TREE_OBJECTID, DEFINE_NAME("raid-stripe") },
77 { .id = 0, DEFINE_NAME("tree") },
78 };
79
80 #undef DEFINE_LEVEL
81 #undef DEFINE_NAME
82
83 void btrfs_set_buffer_lockdep_class(u64 objectid, struct extent_buffer *eb, int level)
84 {
85 struct btrfs_lockdep_keyset *ks;
86
87 ASSERT(level < ARRAY_SIZE(ks->keys));
88
89 /* Find the matching keyset, id 0 is the default entry */
90 for (ks = btrfs_lockdep_keysets; ks->id; ks++)
91 if (ks->id == objectid)
92 break;
93
94 lockdep_set_class_and_name(&eb->lock, &ks->keys[level], ks->names[level]);
95 }
96
97 void btrfs_maybe_reset_lockdep_class(struct btrfs_root *root, struct extent_buffer *eb)
98 {
99 if (test_bit(BTRFS_ROOT_RESET_LOCKDEP_CLASS, &root->state))
100 btrfs_set_buffer_lockdep_class(btrfs_root_id(root),
101 eb, btrfs_header_level(eb));
102 }
103
104 #endif
105
106 #ifdef CONFIG_BTRFS_DEBUG
107 static void btrfs_set_eb_lock_owner(struct extent_buffer *eb, pid_t owner)
108 {
109 eb->lock_owner = owner;
110 }
111 #else
112 static void btrfs_set_eb_lock_owner(struct extent_buffer *eb, pid_t owner) { }
113 #endif
114
115 /*
116 * Extent buffer locking
117 * =====================
118 *
119 * We use a rw_semaphore for tree locking, and the semantics are exactly the
120 * same:
121 *
122 * - reader/writer exclusion
123 * - writer/writer exclusion
124 * - reader/reader sharing
125 * - try-lock semantics for readers and writers
126 *
127 * The rwsem implementation does opportunistic spinning which reduces number of
128 * times the locking task needs to sleep.
129 */
130
131 /*
132 * btrfs_tree_read_lock_nested - lock extent buffer for read
133 * @eb: the eb to be locked
134 * @nest: the nesting level to be used for lockdep
135 *
136 * This takes the read lock on the extent buffer, using the specified nesting
137 * level for lockdep purposes.
138 */
139 void btrfs_tree_read_lock_nested(struct extent_buffer *eb, enum btrfs_lock_nesting nest)
140 {
141 u64 start_ns = 0;
142
143 if (trace_btrfs_tree_read_lock_enabled())
144 start_ns = ktime_get_ns();
145
146 down_read_nested(&eb->lock, nest);
147 trace_btrfs_tree_read_lock(eb, start_ns);
148 }
149
150 /*
151 * Try-lock for read.
152 *
153 * Return 1 if the rwlock has been taken, 0 otherwise
154 */
155 int btrfs_try_tree_read_lock(struct extent_buffer *eb)
156 {
157 if (down_read_trylock(&eb->lock)) {
158 trace_btrfs_try_tree_read_lock(eb);
159 return 1;
160 }
161 return 0;
162 }
163
164 /*
165 * Try-lock for write.
166 *
167 * Return 1 if the rwlock has been taken, 0 otherwise
168 */
169 int btrfs_try_tree_write_lock(struct extent_buffer *eb)
170 {
171 if (down_write_trylock(&eb->lock)) {
172 btrfs_set_eb_lock_owner(eb, current->pid);
173 trace_btrfs_try_tree_write_lock(eb);
174 return 1;
175 }
176 return 0;
177 }
178
179 /*
180 * Release read lock.
181 */
182 void btrfs_tree_read_unlock(struct extent_buffer *eb)
183 {
184 trace_btrfs_tree_read_unlock(eb);
185 up_read(&eb->lock);
186 }
187
188 /*
189 * Lock eb for write.
190 *
191 * @eb: the eb to lock
192 * @nest: the nesting to use for the lock
193 *
194 * Returns with the eb->lock write locked.
195 */
196 void btrfs_tree_lock_nested(struct extent_buffer *eb, enum btrfs_lock_nesting nest)
197 __acquires(&eb->lock)
198 {
199 u64 start_ns = 0;
200
201 if (trace_btrfs_tree_lock_enabled())
202 start_ns = ktime_get_ns();
203
204 down_write_nested(&eb->lock, nest);
205 btrfs_set_eb_lock_owner(eb, current->pid);
206 trace_btrfs_tree_lock(eb, start_ns);
207 }
208
209 /*
210 * Release the write lock.
211 */
212 void btrfs_tree_unlock(struct extent_buffer *eb)
213 {
214 trace_btrfs_tree_unlock(eb);
215 btrfs_set_eb_lock_owner(eb, 0);
216 up_write(&eb->lock);
217 }
218
219 /*
220 * This releases any locks held in the path starting at level and going all the
221 * way up to the root.
222 *
223 * btrfs_search_slot will keep the lock held on higher nodes in a few corner
224 * cases, such as COW of the block at slot zero in the node. This ignores
225 * those rules, and it should only be called when there are no more updates to
226 * be done higher up in the tree.
227 */
228 void btrfs_unlock_up_safe(struct btrfs_path *path, int level)
229 {
230 int i;
231
232 if (path->keep_locks)
233 return;
234
235 for (i = level; i < BTRFS_MAX_LEVEL; i++) {
236 if (!path->nodes[i])
237 continue;
238 if (!path->locks[i])
239 continue;
240 btrfs_tree_unlock_rw(path->nodes[i], path->locks[i]);
241 path->locks[i] = 0;
242 }
243 }
244
245 /*
246 * Loop around taking references on and locking the root node of the tree until
247 * we end up with a lock on the root node.
248 *
249 * Return: root extent buffer with write lock held
250 */
251 struct extent_buffer *btrfs_lock_root_node(struct btrfs_root *root)
252 {
253 struct extent_buffer *eb;
254
255 while (1) {
256 eb = btrfs_root_node(root);
257
258 btrfs_maybe_reset_lockdep_class(root, eb);
259 btrfs_tree_lock(eb);
260 if (eb == root->node)
261 break;
262 btrfs_tree_unlock(eb);
263 free_extent_buffer(eb);
264 }
265 return eb;
266 }
267
268 /*
269 * Loop around taking references on and locking the root node of the tree until
270 * we end up with a lock on the root node.
271 *
272 * Return: root extent buffer with read lock held
273 */
274 struct extent_buffer *btrfs_read_lock_root_node(struct btrfs_root *root)
275 {
276 struct extent_buffer *eb;
277
278 while (1) {
279 eb = btrfs_root_node(root);
280
281 btrfs_maybe_reset_lockdep_class(root, eb);
282 btrfs_tree_read_lock(eb);
283 if (eb == root->node)
284 break;
285 btrfs_tree_read_unlock(eb);
286 free_extent_buffer(eb);
287 }
288 return eb;
289 }
290
291 /*
292 * Loop around taking references on and locking the root node of the tree in
293 * nowait mode until we end up with a lock on the root node or returning to
294 * avoid blocking.
295 *
296 * Return: root extent buffer with read lock held or -EAGAIN.
297 */
298 struct extent_buffer *btrfs_try_read_lock_root_node(struct btrfs_root *root)
299 {
300 struct extent_buffer *eb;
301
302 while (1) {
303 eb = btrfs_root_node(root);
304 if (!btrfs_try_tree_read_lock(eb)) {
305 free_extent_buffer(eb);
306 return ERR_PTR(-EAGAIN);
307 }
308 if (eb == root->node)
309 break;
310 btrfs_tree_read_unlock(eb);
311 free_extent_buffer(eb);
312 }
313 return eb;
314 }
315
316 /*
317 * DREW locks
318 * ==========
319 *
320 * DREW stands for double-reader-writer-exclusion lock. It's used in situation
321 * where you want to provide A-B exclusion but not AA or BB.
322 *
323 * Currently implementation gives more priority to reader. If a reader and a
324 * writer both race to acquire their respective sides of the lock the writer
325 * would yield its lock as soon as it detects a concurrent reader. Additionally
326 * if there are pending readers no new writers would be allowed to come in and
327 * acquire the lock.
328 */
329
330 void btrfs_drew_lock_init(struct btrfs_drew_lock *lock)
331 {
332 atomic_set(&lock->readers, 0);
333 atomic_set(&lock->writers, 0);
334 init_waitqueue_head(&lock->pending_readers);
335 init_waitqueue_head(&lock->pending_writers);
336 }
337
338 /* Return true if acquisition is successful, false otherwise */
339 bool btrfs_drew_try_write_lock(struct btrfs_drew_lock *lock)
340 {
341 if (atomic_read(&lock->readers))
342 return false;
343
344 atomic_inc(&lock->writers);
345
346 /* Ensure writers count is updated before we check for pending readers */
347 smp_mb__after_atomic();
348 if (atomic_read(&lock->readers)) {
349 btrfs_drew_write_unlock(lock);
350 return false;
351 }
352
353 return true;
354 }
355
356 void btrfs_drew_write_lock(struct btrfs_drew_lock *lock)
357 {
358 while (true) {
359 if (btrfs_drew_try_write_lock(lock))
360 return;
361 wait_event(lock->pending_writers, !atomic_read(&lock->readers));
362 }
363 }
364
365 void btrfs_drew_write_unlock(struct btrfs_drew_lock *lock)
366 {
367 /*
368 * atomic_dec_and_test() implies a full barrier, so woken up readers are
369 * guaranteed to see the decrement.
370 */
371 if (atomic_dec_and_test(&lock->writers))
372 wake_up(&lock->pending_readers);
373 }
374
375 void btrfs_drew_read_lock(struct btrfs_drew_lock *lock)
376 {
377 atomic_inc(&lock->readers);
378
379 /*
380 * Ensure the pending reader count is perceieved BEFORE this reader
381 * goes to sleep in case of active writers. This guarantees new writers
382 * won't be allowed and that the current reader will be woken up when
383 * the last active writer finishes its jobs.
384 */
385 smp_mb__after_atomic();
386
387 wait_event(lock->pending_readers, atomic_read(&lock->writers) == 0);
388 }
389
390 void btrfs_drew_read_unlock(struct btrfs_drew_lock *lock)
391 {
392 /*
393 * atomic_dec_and_test implies a full barrier, so woken up writers
394 * are guaranteed to see the decrement
395 */
396 if (atomic_dec_and_test(&lock->readers))
397 wake_up(&lock->pending_writers);
398 }
399
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