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(root->root_key.objectid, 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 - 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(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 void btrfs_tree_read_lock(struct extent_buffer *eb) 151 { 152 __btrfs_tree_read_lock(eb, BTRFS_NESTING_NORMAL); 153 } 154 155 /* 156 * Try-lock for read. 157 * 158 * Return 1 if the rwlock has been taken, 0 otherwise 159 */ 160 int btrfs_try_tree_read_lock(struct extent_buffer *eb) 161 { 162 if (down_read_trylock(&eb->lock)) { 163 trace_btrfs_try_tree_read_lock(eb); 164 return 1; 165 } 166 return 0; 167 } 168 169 /* 170 * Try-lock for write. 171 * 172 * Return 1 if the rwlock has been taken, 0 otherwise 173 */ 174 int btrfs_try_tree_write_lock(struct extent_buffer *eb) 175 { 176 if (down_write_trylock(&eb->lock)) { 177 btrfs_set_eb_lock_owner(eb, current->pid); 178 trace_btrfs_try_tree_write_lock(eb); 179 return 1; 180 } 181 return 0; 182 } 183 184 /* 185 * Release read lock. 186 */ 187 void btrfs_tree_read_unlock(struct extent_buffer *eb) 188 { 189 trace_btrfs_tree_read_unlock(eb); 190 up_read(&eb->lock); 191 } 192 193 /* 194 * Lock eb for write. 195 * 196 * @eb: the eb to lock 197 * @nest: the nesting to use for the lock 198 * 199 * Returns with the eb->lock write locked. 200 */ 201 void __btrfs_tree_lock(struct extent_buffer *eb, enum btrfs_lock_nesting nest) 202 __acquires(&eb->lock) 203 { 204 u64 start_ns = 0; 205 206 if (trace_btrfs_tree_lock_enabled()) 207 start_ns = ktime_get_ns(); 208 209 down_write_nested(&eb->lock, nest); 210 btrfs_set_eb_lock_owner(eb, current->pid); 211 trace_btrfs_tree_lock(eb, start_ns); 212 } 213 214 void btrfs_tree_lock(struct extent_buffer *eb) 215 { 216 __btrfs_tree_lock(eb, BTRFS_NESTING_NORMAL); 217 } 218 219 /* 220 * Release the write lock. 221 */ 222 void btrfs_tree_unlock(struct extent_buffer *eb) 223 { 224 trace_btrfs_tree_unlock(eb); 225 btrfs_set_eb_lock_owner(eb, 0); 226 up_write(&eb->lock); 227 } 228 229 /* 230 * This releases any locks held in the path starting at level and going all the 231 * way up to the root. 232 * 233 * btrfs_search_slot will keep the lock held on higher nodes in a few corner 234 * cases, such as COW of the block at slot zero in the node. This ignores 235 * those rules, and it should only be called when there are no more updates to 236 * be done higher up in the tree. 237 */ 238 void btrfs_unlock_up_safe(struct btrfs_path *path, int level) 239 { 240 int i; 241 242 if (path->keep_locks) 243 return; 244 245 for (i = level; i < BTRFS_MAX_LEVEL; i++) { 246 if (!path->nodes[i]) 247 continue; 248 if (!path->locks[i]) 249 continue; 250 btrfs_tree_unlock_rw(path->nodes[i], path->locks[i]); 251 path->locks[i] = 0; 252 } 253 } 254 255 /* 256 * Loop around taking references on and locking the root node of the tree until 257 * we end up with a lock on the root node. 258 * 259 * Return: root extent buffer with write lock held 260 */ 261 struct extent_buffer *btrfs_lock_root_node(struct btrfs_root *root) 262 { 263 struct extent_buffer *eb; 264 265 while (1) { 266 eb = btrfs_root_node(root); 267 268 btrfs_maybe_reset_lockdep_class(root, eb); 269 btrfs_tree_lock(eb); 270 if (eb == root->node) 271 break; 272 btrfs_tree_unlock(eb); 273 free_extent_buffer(eb); 274 } 275 return eb; 276 } 277 278 /* 279 * Loop around taking references on and locking the root node of the tree until 280 * we end up with a lock on the root node. 281 * 282 * Return: root extent buffer with read lock held 283 */ 284 struct extent_buffer *btrfs_read_lock_root_node(struct btrfs_root *root) 285 { 286 struct extent_buffer *eb; 287 288 while (1) { 289 eb = btrfs_root_node(root); 290 291 btrfs_maybe_reset_lockdep_class(root, eb); 292 btrfs_tree_read_lock(eb); 293 if (eb == root->node) 294 break; 295 btrfs_tree_read_unlock(eb); 296 free_extent_buffer(eb); 297 } 298 return eb; 299 } 300 301 /* 302 * Loop around taking references on and locking the root node of the tree in 303 * nowait mode until we end up with a lock on the root node or returning to 304 * avoid blocking. 305 * 306 * Return: root extent buffer with read lock held or -EAGAIN. 307 */ 308 struct extent_buffer *btrfs_try_read_lock_root_node(struct btrfs_root *root) 309 { 310 struct extent_buffer *eb; 311 312 while (1) { 313 eb = btrfs_root_node(root); 314 if (!btrfs_try_tree_read_lock(eb)) { 315 free_extent_buffer(eb); 316 return ERR_PTR(-EAGAIN); 317 } 318 if (eb == root->node) 319 break; 320 btrfs_tree_read_unlock(eb); 321 free_extent_buffer(eb); 322 } 323 return eb; 324 } 325 326 /* 327 * DREW locks 328 * ========== 329 * 330 * DREW stands for double-reader-writer-exclusion lock. It's used in situation 331 * where you want to provide A-B exclusion but not AA or BB. 332 * 333 * Currently implementation gives more priority to reader. If a reader and a 334 * writer both race to acquire their respective sides of the lock the writer 335 * would yield its lock as soon as it detects a concurrent reader. Additionally 336 * if there are pending readers no new writers would be allowed to come in and 337 * acquire the lock. 338 */ 339 340 void btrfs_drew_lock_init(struct btrfs_drew_lock *lock) 341 { 342 atomic_set(&lock->readers, 0); 343 atomic_set(&lock->writers, 0); 344 init_waitqueue_head(&lock->pending_readers); 345 init_waitqueue_head(&lock->pending_writers); 346 } 347 348 /* Return true if acquisition is successful, false otherwise */ 349 bool btrfs_drew_try_write_lock(struct btrfs_drew_lock *lock) 350 { 351 if (atomic_read(&lock->readers)) 352 return false; 353 354 atomic_inc(&lock->writers); 355 356 /* Ensure writers count is updated before we check for pending readers */ 357 smp_mb__after_atomic(); 358 if (atomic_read(&lock->readers)) { 359 btrfs_drew_write_unlock(lock); 360 return false; 361 } 362 363 return true; 364 } 365 366 void btrfs_drew_write_lock(struct btrfs_drew_lock *lock) 367 { 368 while (true) { 369 if (btrfs_drew_try_write_lock(lock)) 370 return; 371 wait_event(lock->pending_writers, !atomic_read(&lock->readers)); 372 } 373 } 374 375 void btrfs_drew_write_unlock(struct btrfs_drew_lock *lock) 376 { 377 atomic_dec(&lock->writers); 378 cond_wake_up(&lock->pending_readers); 379 } 380 381 void btrfs_drew_read_lock(struct btrfs_drew_lock *lock) 382 { 383 atomic_inc(&lock->readers); 384 385 /* 386 * Ensure the pending reader count is perceieved BEFORE this reader 387 * goes to sleep in case of active writers. This guarantees new writers 388 * won't be allowed and that the current reader will be woken up when 389 * the last active writer finishes its jobs. 390 */ 391 smp_mb__after_atomic(); 392 393 wait_event(lock->pending_readers, atomic_read(&lock->writers) == 0); 394 } 395 396 void btrfs_drew_read_unlock(struct btrfs_drew_lock *lock) 397 { 398 /* 399 * atomic_dec_and_test implies a full barrier, so woken up writers 400 * are guaranteed to see the decrement 401 */ 402 if (atomic_dec_and_test(&lock->readers)) 403 wake_up(&lock->pending_writers); 404 } 405