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 #include "accessors.h" 17 18 /* 19 * Lockdep class keys for extent_buffer->lock's in this root. For a given 20 * eb, the lockdep key is determined by the btrfs_root it belongs to and 21 * the level the eb occupies in the tree. 22 * 23 * Different roots are used for different purposes and may nest inside each 24 * other and they require separate keysets. As lockdep keys should be 25 * static, assign keysets according to the purpose of the root as indicated 26 * by btrfs_root->root_key.objectid. This ensures that all special purpose 27 * roots have separate keysets. 28 * 29 * Lock-nesting across peer nodes is always done with the immediate parent 30 * node locked thus preventing deadlock. As lockdep doesn't know this, use 31 * subclass to avoid triggering lockdep warning in such cases. 32 * 33 * The key is set by the readpage_end_io_hook after the buffer has passed 34 * csum validation but before the pages are unlocked. It is also set by 35 * btrfs_init_new_buffer on freshly allocated blocks. 36 * 37 * We also add a check to make sure the highest level of the tree is the 38 * same as our lockdep setup here. If BTRFS_MAX_LEVEL changes, this code 39 * needs update as well. 40 */ 41 #ifdef CONFIG_DEBUG_LOCK_ALLOC 42 #if BTRFS_MAX_LEVEL != 8 43 #error 44 #endif 45 46 #define DEFINE_LEVEL(stem, level) \ 47 .names[level] = "btrfs-" stem "-0" #level, 48 49 #define DEFINE_NAME(stem) \ 50 DEFINE_LEVEL(stem, 0) \ 51 DEFINE_LEVEL(stem, 1) \ 52 DEFINE_LEVEL(stem, 2) \ 53 DEFINE_LEVEL(stem, 3) \ 54 DEFINE_LEVEL(stem, 4) \ 55 DEFINE_LEVEL(stem, 5) \ 56 DEFINE_LEVEL(stem, 6) \ 57 DEFINE_LEVEL(stem, 7) 58 59 static struct btrfs_lockdep_keyset { 60 u64 id; /* root objectid */ 61 /* Longest entry: btrfs-block-group-00 */ 62 char names[BTRFS_MAX_LEVEL][24]; 63 struct lock_class_key keys[BTRFS_MAX_LEVEL]; 64 } btrfs_lockdep_keysets[] = { 65 { .id = BTRFS_ROOT_TREE_OBJECTID, DEFINE_NAME("root") }, 66 { .id = BTRFS_EXTENT_TREE_OBJECTID, DEFINE_NAME("extent") }, 67 { .id = BTRFS_CHUNK_TREE_OBJECTID, DEFINE_NAME("chunk") }, 68 { .id = BTRFS_DEV_TREE_OBJECTID, DEFINE_NAME("dev") }, 69 { .id = BTRFS_CSUM_TREE_OBJECTID, DEFINE_NAME("csum") }, 70 { .id = BTRFS_QUOTA_TREE_OBJECTID, DEFINE_NAME("quota") }, 71 { .id = BTRFS_TREE_LOG_OBJECTID, DEFINE_NAME("log") }, 72 { .id = BTRFS_TREE_RELOC_OBJECTID, DEFINE_NAME("treloc") }, 73 { .id = BTRFS_DATA_RELOC_TREE_OBJECTID, DEFINE_NAME("dreloc") }, 74 { .id = BTRFS_UUID_TREE_OBJECTID, DEFINE_NAME("uuid") }, 75 { .id = BTRFS_FREE_SPACE_TREE_OBJECTID, DEFINE_NAME("free-space") }, 76 { .id = BTRFS_BLOCK_GROUP_TREE_OBJECTID, DEFINE_NAME("block-group") }, 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 BUG_ON(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 /* 107 * Extent buffer locking 108 * ===================== 109 * 110 * We use a rw_semaphore for tree locking, and the semantics are exactly the 111 * same: 112 * 113 * - reader/writer exclusion 114 * - writer/writer exclusion 115 * - reader/reader sharing 116 * - try-lock semantics for readers and writers 117 * 118 * The rwsem implementation does opportunistic spinning which reduces number of 119 * times the locking task needs to sleep. 120 */ 121 122 /* 123 * __btrfs_tree_read_lock - lock extent buffer for read 124 * @eb: the eb to be locked 125 * @nest: the nesting level to be used for lockdep 126 * 127 * This takes the read lock on the extent buffer, using the specified nesting 128 * level for lockdep purposes. 129 */ 130 void __btrfs_tree_read_lock(struct extent_buffer *eb, enum btrfs_lock_nesting nest) 131 { 132 u64 start_ns = 0; 133 134 if (trace_btrfs_tree_read_lock_enabled()) 135 start_ns = ktime_get_ns(); 136 137 down_read_nested(&eb->lock, nest); 138 trace_btrfs_tree_read_lock(eb, start_ns); 139 } 140 141 void btrfs_tree_read_lock(struct extent_buffer *eb) 142 { 143 __btrfs_tree_read_lock(eb, BTRFS_NESTING_NORMAL); 144 } 145 146 /* 147 * Try-lock for read. 148 * 149 * Return 1 if the rwlock has been taken, 0 otherwise 150 */ 151 int btrfs_try_tree_read_lock(struct extent_buffer *eb) 152 { 153 if (down_read_trylock(&eb->lock)) { 154 trace_btrfs_try_tree_read_lock(eb); 155 return 1; 156 } 157 return 0; 158 } 159 160 /* 161 * Try-lock for write. 162 * 163 * Return 1 if the rwlock has been taken, 0 otherwise 164 */ 165 int btrfs_try_tree_write_lock(struct extent_buffer *eb) 166 { 167 if (down_write_trylock(&eb->lock)) { 168 eb->lock_owner = current->pid; 169 trace_btrfs_try_tree_write_lock(eb); 170 return 1; 171 } 172 return 0; 173 } 174 175 /* 176 * Release read lock. 177 */ 178 void btrfs_tree_read_unlock(struct extent_buffer *eb) 179 { 180 trace_btrfs_tree_read_unlock(eb); 181 up_read(&eb->lock); 182 } 183 184 /* 185 * __btrfs_tree_lock - lock eb for write 186 * @eb: the eb to lock 187 * @nest: the nesting to use for the lock 188 * 189 * Returns with the eb->lock write locked. 190 */ 191 void __btrfs_tree_lock(struct extent_buffer *eb, enum btrfs_lock_nesting nest) 192 __acquires(&eb->lock) 193 { 194 u64 start_ns = 0; 195 196 if (trace_btrfs_tree_lock_enabled()) 197 start_ns = ktime_get_ns(); 198 199 down_write_nested(&eb->lock, nest); 200 eb->lock_owner = current->pid; 201 trace_btrfs_tree_lock(eb, start_ns); 202 } 203 204 void btrfs_tree_lock(struct extent_buffer *eb) 205 { 206 __btrfs_tree_lock(eb, BTRFS_NESTING_NORMAL); 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 eb->lock_owner = 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 atomic_dec(&lock->writers); 368 cond_wake_up(&lock->pending_readers); 369 } 370 371 void btrfs_drew_read_lock(struct btrfs_drew_lock *lock) 372 { 373 atomic_inc(&lock->readers); 374 375 /* 376 * Ensure the pending reader count is perceieved BEFORE this reader 377 * goes to sleep in case of active writers. This guarantees new writers 378 * won't be allowed and that the current reader will be woken up when 379 * the last active writer finishes its jobs. 380 */ 381 smp_mb__after_atomic(); 382 383 wait_event(lock->pending_readers, atomic_read(&lock->writers) == 0); 384 } 385 386 void btrfs_drew_read_unlock(struct btrfs_drew_lock *lock) 387 { 388 /* 389 * atomic_dec_and_test implies a full barrier, so woken up writers 390 * are guaranteed to see the decrement 391 */ 392 if (atomic_dec_and_test(&lock->readers)) 393 wake_up(&lock->pending_writers); 394 } 395