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