| 1 | /* |
| 2 | * kernel/locking/mutex.c |
| 3 | * |
| 4 | * Mutexes: blocking mutual exclusion locks |
| 5 | * |
| 6 | * Started by Ingo Molnar: |
| 7 | * |
| 8 | * Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com> |
| 9 | * |
| 10 | * Many thanks to Arjan van de Ven, Thomas Gleixner, Steven Rostedt and |
| 11 | * David Howells for suggestions and improvements. |
| 12 | * |
| 13 | * - Adaptive spinning for mutexes by Peter Zijlstra. (Ported to mainline |
| 14 | * from the -rt tree, where it was originally implemented for rtmutexes |
| 15 | * by Steven Rostedt, based on work by Gregory Haskins, Peter Morreale |
| 16 | * and Sven Dietrich. |
| 17 | * |
| 18 | * Also see Documentation/locking/mutex-design.txt. |
| 19 | */ |
| 20 | #include <linux/mutex.h> |
| 21 | #include <linux/ww_mutex.h> |
| 22 | #include <linux/sched.h> |
| 23 | #include <linux/sched/rt.h> |
| 24 | #include <linux/export.h> |
| 25 | #include <linux/spinlock.h> |
| 26 | #include <linux/interrupt.h> |
| 27 | #include <linux/debug_locks.h> |
| 28 | #include <linux/osq_lock.h> |
| 29 | |
| 30 | /* |
| 31 | * In the DEBUG case we are using the "NULL fastpath" for mutexes, |
| 32 | * which forces all calls into the slowpath: |
| 33 | */ |
| 34 | #ifdef CONFIG_DEBUG_MUTEXES |
| 35 | # include "mutex-debug.h" |
| 36 | # include <asm-generic/mutex-null.h> |
| 37 | /* |
| 38 | * Must be 0 for the debug case so we do not do the unlock outside of the |
| 39 | * wait_lock region. debug_mutex_unlock() will do the actual unlock in this |
| 40 | * case. |
| 41 | */ |
| 42 | # undef __mutex_slowpath_needs_to_unlock |
| 43 | # define __mutex_slowpath_needs_to_unlock() 0 |
| 44 | #else |
| 45 | # include "mutex.h" |
| 46 | # include <asm/mutex.h> |
| 47 | #endif |
| 48 | |
| 49 | void |
| 50 | __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key) |
| 51 | { |
| 52 | atomic_set(&lock->count, 1); |
| 53 | spin_lock_init(&lock->wait_lock); |
| 54 | INIT_LIST_HEAD(&lock->wait_list); |
| 55 | mutex_clear_owner(lock); |
| 56 | #ifdef CONFIG_MUTEX_SPIN_ON_OWNER |
| 57 | osq_lock_init(&lock->osq); |
| 58 | #endif |
| 59 | |
| 60 | debug_mutex_init(lock, name, key); |
| 61 | } |
| 62 | |
| 63 | EXPORT_SYMBOL(__mutex_init); |
| 64 | |
| 65 | #ifndef CONFIG_DEBUG_LOCK_ALLOC |
| 66 | /* |
| 67 | * We split the mutex lock/unlock logic into separate fastpath and |
| 68 | * slowpath functions, to reduce the register pressure on the fastpath. |
| 69 | * We also put the fastpath first in the kernel image, to make sure the |
| 70 | * branch is predicted by the CPU as default-untaken. |
| 71 | */ |
| 72 | __visible void __sched __mutex_lock_slowpath(atomic_t *lock_count); |
| 73 | |
| 74 | /** |
| 75 | * mutex_lock - acquire the mutex |
| 76 | * @lock: the mutex to be acquired |
| 77 | * |
| 78 | * Lock the mutex exclusively for this task. If the mutex is not |
| 79 | * available right now, it will sleep until it can get it. |
| 80 | * |
| 81 | * The mutex must later on be released by the same task that |
| 82 | * acquired it. Recursive locking is not allowed. The task |
| 83 | * may not exit without first unlocking the mutex. Also, kernel |
| 84 | * memory where the mutex resides must not be freed with |
| 85 | * the mutex still locked. The mutex must first be initialized |
| 86 | * (or statically defined) before it can be locked. memset()-ing |
| 87 | * the mutex to 0 is not allowed. |
| 88 | * |
| 89 | * ( The CONFIG_DEBUG_MUTEXES .config option turns on debugging |
| 90 | * checks that will enforce the restrictions and will also do |
| 91 | * deadlock debugging. ) |
| 92 | * |
| 93 | * This function is similar to (but not equivalent to) down(). |
| 94 | */ |
| 95 | void __sched mutex_lock(struct mutex *lock) |
| 96 | { |
| 97 | might_sleep(); |
| 98 | /* |
| 99 | * The locking fastpath is the 1->0 transition from |
| 100 | * 'unlocked' into 'locked' state. |
| 101 | */ |
| 102 | __mutex_fastpath_lock(&lock->count, __mutex_lock_slowpath); |
| 103 | mutex_set_owner(lock); |
| 104 | } |
| 105 | |
| 106 | EXPORT_SYMBOL(mutex_lock); |
| 107 | #endif |
| 108 | |
| 109 | static __always_inline void ww_mutex_lock_acquired(struct ww_mutex *ww, |
| 110 | struct ww_acquire_ctx *ww_ctx) |
| 111 | { |
| 112 | #ifdef CONFIG_DEBUG_MUTEXES |
| 113 | /* |
| 114 | * If this WARN_ON triggers, you used ww_mutex_lock to acquire, |
| 115 | * but released with a normal mutex_unlock in this call. |
| 116 | * |
| 117 | * This should never happen, always use ww_mutex_unlock. |
| 118 | */ |
| 119 | DEBUG_LOCKS_WARN_ON(ww->ctx); |
| 120 | |
| 121 | /* |
| 122 | * Not quite done after calling ww_acquire_done() ? |
| 123 | */ |
| 124 | DEBUG_LOCKS_WARN_ON(ww_ctx->done_acquire); |
| 125 | |
| 126 | if (ww_ctx->contending_lock) { |
| 127 | /* |
| 128 | * After -EDEADLK you tried to |
| 129 | * acquire a different ww_mutex? Bad! |
| 130 | */ |
| 131 | DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock != ww); |
| 132 | |
| 133 | /* |
| 134 | * You called ww_mutex_lock after receiving -EDEADLK, |
| 135 | * but 'forgot' to unlock everything else first? |
| 136 | */ |
| 137 | DEBUG_LOCKS_WARN_ON(ww_ctx->acquired > 0); |
| 138 | ww_ctx->contending_lock = NULL; |
| 139 | } |
| 140 | |
| 141 | /* |
| 142 | * Naughty, using a different class will lead to undefined behavior! |
| 143 | */ |
| 144 | DEBUG_LOCKS_WARN_ON(ww_ctx->ww_class != ww->ww_class); |
| 145 | #endif |
| 146 | ww_ctx->acquired++; |
| 147 | } |
| 148 | |
| 149 | /* |
| 150 | * After acquiring lock with fastpath or when we lost out in contested |
| 151 | * slowpath, set ctx and wake up any waiters so they can recheck. |
| 152 | * |
| 153 | * This function is never called when CONFIG_DEBUG_LOCK_ALLOC is set, |
| 154 | * as the fastpath and opportunistic spinning are disabled in that case. |
| 155 | */ |
| 156 | static __always_inline void |
| 157 | ww_mutex_set_context_fastpath(struct ww_mutex *lock, |
| 158 | struct ww_acquire_ctx *ctx) |
| 159 | { |
| 160 | unsigned long flags; |
| 161 | struct mutex_waiter *cur; |
| 162 | |
| 163 | ww_mutex_lock_acquired(lock, ctx); |
| 164 | |
| 165 | lock->ctx = ctx; |
| 166 | |
| 167 | /* |
| 168 | * The lock->ctx update should be visible on all cores before |
| 169 | * the atomic read is done, otherwise contended waiters might be |
| 170 | * missed. The contended waiters will either see ww_ctx == NULL |
| 171 | * and keep spinning, or it will acquire wait_lock, add itself |
| 172 | * to waiter list and sleep. |
| 173 | */ |
| 174 | smp_mb(); /* ^^^ */ |
| 175 | |
| 176 | /* |
| 177 | * Check if lock is contended, if not there is nobody to wake up |
| 178 | */ |
| 179 | if (likely(atomic_read(&lock->base.count) == 0)) |
| 180 | return; |
| 181 | |
| 182 | /* |
| 183 | * Uh oh, we raced in fastpath, wake up everyone in this case, |
| 184 | * so they can see the new lock->ctx. |
| 185 | */ |
| 186 | spin_lock_mutex(&lock->base.wait_lock, flags); |
| 187 | list_for_each_entry(cur, &lock->base.wait_list, list) { |
| 188 | debug_mutex_wake_waiter(&lock->base, cur); |
| 189 | wake_up_process(cur->task); |
| 190 | } |
| 191 | spin_unlock_mutex(&lock->base.wait_lock, flags); |
| 192 | } |
| 193 | |
| 194 | /* |
| 195 | * After acquiring lock in the slowpath set ctx and wake up any |
| 196 | * waiters so they can recheck. |
| 197 | * |
| 198 | * Callers must hold the mutex wait_lock. |
| 199 | */ |
| 200 | static __always_inline void |
| 201 | ww_mutex_set_context_slowpath(struct ww_mutex *lock, |
| 202 | struct ww_acquire_ctx *ctx) |
| 203 | { |
| 204 | struct mutex_waiter *cur; |
| 205 | |
| 206 | ww_mutex_lock_acquired(lock, ctx); |
| 207 | lock->ctx = ctx; |
| 208 | |
| 209 | /* |
| 210 | * Give any possible sleeping processes the chance to wake up, |
| 211 | * so they can recheck if they have to back off. |
| 212 | */ |
| 213 | list_for_each_entry(cur, &lock->base.wait_list, list) { |
| 214 | debug_mutex_wake_waiter(&lock->base, cur); |
| 215 | wake_up_process(cur->task); |
| 216 | } |
| 217 | } |
| 218 | |
| 219 | #ifdef CONFIG_MUTEX_SPIN_ON_OWNER |
| 220 | /* |
| 221 | * Look out! "owner" is an entirely speculative pointer |
| 222 | * access and not reliable. |
| 223 | */ |
| 224 | static noinline |
| 225 | bool mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner) |
| 226 | { |
| 227 | bool ret = true; |
| 228 | |
| 229 | rcu_read_lock(); |
| 230 | while (lock->owner == owner) { |
| 231 | /* |
| 232 | * Ensure we emit the owner->on_cpu, dereference _after_ |
| 233 | * checking lock->owner still matches owner. If that fails, |
| 234 | * owner might point to freed memory. If it still matches, |
| 235 | * the rcu_read_lock() ensures the memory stays valid. |
| 236 | */ |
| 237 | barrier(); |
| 238 | |
| 239 | if (!owner->on_cpu || need_resched()) { |
| 240 | ret = false; |
| 241 | break; |
| 242 | } |
| 243 | |
| 244 | cpu_relax_lowlatency(); |
| 245 | } |
| 246 | rcu_read_unlock(); |
| 247 | |
| 248 | return ret; |
| 249 | } |
| 250 | |
| 251 | /* |
| 252 | * Initial check for entering the mutex spinning loop |
| 253 | */ |
| 254 | static inline int mutex_can_spin_on_owner(struct mutex *lock) |
| 255 | { |
| 256 | struct task_struct *owner; |
| 257 | int retval = 1; |
| 258 | |
| 259 | if (need_resched()) |
| 260 | return 0; |
| 261 | |
| 262 | rcu_read_lock(); |
| 263 | owner = READ_ONCE(lock->owner); |
| 264 | if (owner) |
| 265 | retval = owner->on_cpu; |
| 266 | rcu_read_unlock(); |
| 267 | /* |
| 268 | * if lock->owner is not set, the mutex owner may have just acquired |
| 269 | * it and not set the owner yet or the mutex has been released. |
| 270 | */ |
| 271 | return retval; |
| 272 | } |
| 273 | |
| 274 | /* |
| 275 | * Atomically try to take the lock when it is available |
| 276 | */ |
| 277 | static inline bool mutex_try_to_acquire(struct mutex *lock) |
| 278 | { |
| 279 | return !mutex_is_locked(lock) && |
| 280 | (atomic_cmpxchg_acquire(&lock->count, 1, 0) == 1); |
| 281 | } |
| 282 | |
| 283 | /* |
| 284 | * Optimistic spinning. |
| 285 | * |
| 286 | * We try to spin for acquisition when we find that the lock owner |
| 287 | * is currently running on a (different) CPU and while we don't |
| 288 | * need to reschedule. The rationale is that if the lock owner is |
| 289 | * running, it is likely to release the lock soon. |
| 290 | * |
| 291 | * Since this needs the lock owner, and this mutex implementation |
| 292 | * doesn't track the owner atomically in the lock field, we need to |
| 293 | * track it non-atomically. |
| 294 | * |
| 295 | * We can't do this for DEBUG_MUTEXES because that relies on wait_lock |
| 296 | * to serialize everything. |
| 297 | * |
| 298 | * The mutex spinners are queued up using MCS lock so that only one |
| 299 | * spinner can compete for the mutex. However, if mutex spinning isn't |
| 300 | * going to happen, there is no point in going through the lock/unlock |
| 301 | * overhead. |
| 302 | * |
| 303 | * Returns true when the lock was taken, otherwise false, indicating |
| 304 | * that we need to jump to the slowpath and sleep. |
| 305 | */ |
| 306 | static bool mutex_optimistic_spin(struct mutex *lock, |
| 307 | struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx) |
| 308 | { |
| 309 | struct task_struct *task = current; |
| 310 | |
| 311 | if (!mutex_can_spin_on_owner(lock)) |
| 312 | goto done; |
| 313 | |
| 314 | /* |
| 315 | * In order to avoid a stampede of mutex spinners trying to |
| 316 | * acquire the mutex all at once, the spinners need to take a |
| 317 | * MCS (queued) lock first before spinning on the owner field. |
| 318 | */ |
| 319 | if (!osq_lock(&lock->osq)) |
| 320 | goto done; |
| 321 | |
| 322 | while (true) { |
| 323 | struct task_struct *owner; |
| 324 | |
| 325 | if (use_ww_ctx && ww_ctx->acquired > 0) { |
| 326 | struct ww_mutex *ww; |
| 327 | |
| 328 | ww = container_of(lock, struct ww_mutex, base); |
| 329 | /* |
| 330 | * If ww->ctx is set the contents are undefined, only |
| 331 | * by acquiring wait_lock there is a guarantee that |
| 332 | * they are not invalid when reading. |
| 333 | * |
| 334 | * As such, when deadlock detection needs to be |
| 335 | * performed the optimistic spinning cannot be done. |
| 336 | */ |
| 337 | if (READ_ONCE(ww->ctx)) |
| 338 | break; |
| 339 | } |
| 340 | |
| 341 | /* |
| 342 | * If there's an owner, wait for it to either |
| 343 | * release the lock or go to sleep. |
| 344 | */ |
| 345 | owner = READ_ONCE(lock->owner); |
| 346 | if (owner && !mutex_spin_on_owner(lock, owner)) |
| 347 | break; |
| 348 | |
| 349 | /* Try to acquire the mutex if it is unlocked. */ |
| 350 | if (mutex_try_to_acquire(lock)) { |
| 351 | lock_acquired(&lock->dep_map, ip); |
| 352 | |
| 353 | if (use_ww_ctx) { |
| 354 | struct ww_mutex *ww; |
| 355 | ww = container_of(lock, struct ww_mutex, base); |
| 356 | |
| 357 | ww_mutex_set_context_fastpath(ww, ww_ctx); |
| 358 | } |
| 359 | |
| 360 | mutex_set_owner(lock); |
| 361 | osq_unlock(&lock->osq); |
| 362 | return true; |
| 363 | } |
| 364 | |
| 365 | /* |
| 366 | * When there's no owner, we might have preempted between the |
| 367 | * owner acquiring the lock and setting the owner field. If |
| 368 | * we're an RT task that will live-lock because we won't let |
| 369 | * the owner complete. |
| 370 | */ |
| 371 | if (!owner && (need_resched() || rt_task(task))) |
| 372 | break; |
| 373 | |
| 374 | /* |
| 375 | * The cpu_relax() call is a compiler barrier which forces |
| 376 | * everything in this loop to be re-loaded. We don't need |
| 377 | * memory barriers as we'll eventually observe the right |
| 378 | * values at the cost of a few extra spins. |
| 379 | */ |
| 380 | cpu_relax_lowlatency(); |
| 381 | } |
| 382 | |
| 383 | osq_unlock(&lock->osq); |
| 384 | done: |
| 385 | /* |
| 386 | * If we fell out of the spin path because of need_resched(), |
| 387 | * reschedule now, before we try-lock the mutex. This avoids getting |
| 388 | * scheduled out right after we obtained the mutex. |
| 389 | */ |
| 390 | if (need_resched()) { |
| 391 | /* |
| 392 | * We _should_ have TASK_RUNNING here, but just in case |
| 393 | * we do not, make it so, otherwise we might get stuck. |
| 394 | */ |
| 395 | __set_current_state(TASK_RUNNING); |
| 396 | schedule_preempt_disabled(); |
| 397 | } |
| 398 | |
| 399 | return false; |
| 400 | } |
| 401 | #else |
| 402 | static bool mutex_optimistic_spin(struct mutex *lock, |
| 403 | struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx) |
| 404 | { |
| 405 | return false; |
| 406 | } |
| 407 | #endif |
| 408 | |
| 409 | __visible __used noinline |
| 410 | void __sched __mutex_unlock_slowpath(atomic_t *lock_count); |
| 411 | |
| 412 | /** |
| 413 | * mutex_unlock - release the mutex |
| 414 | * @lock: the mutex to be released |
| 415 | * |
| 416 | * Unlock a mutex that has been locked by this task previously. |
| 417 | * |
| 418 | * This function must not be used in interrupt context. Unlocking |
| 419 | * of a not locked mutex is not allowed. |
| 420 | * |
| 421 | * This function is similar to (but not equivalent to) up(). |
| 422 | */ |
| 423 | void __sched mutex_unlock(struct mutex *lock) |
| 424 | { |
| 425 | /* |
| 426 | * The unlocking fastpath is the 0->1 transition from 'locked' |
| 427 | * into 'unlocked' state: |
| 428 | */ |
| 429 | #ifndef CONFIG_DEBUG_MUTEXES |
| 430 | /* |
| 431 | * When debugging is enabled we must not clear the owner before time, |
| 432 | * the slow path will always be taken, and that clears the owner field |
| 433 | * after verifying that it was indeed current. |
| 434 | */ |
| 435 | mutex_clear_owner(lock); |
| 436 | #endif |
| 437 | __mutex_fastpath_unlock(&lock->count, __mutex_unlock_slowpath); |
| 438 | } |
| 439 | |
| 440 | EXPORT_SYMBOL(mutex_unlock); |
| 441 | |
| 442 | /** |
| 443 | * ww_mutex_unlock - release the w/w mutex |
| 444 | * @lock: the mutex to be released |
| 445 | * |
| 446 | * Unlock a mutex that has been locked by this task previously with any of the |
| 447 | * ww_mutex_lock* functions (with or without an acquire context). It is |
| 448 | * forbidden to release the locks after releasing the acquire context. |
| 449 | * |
| 450 | * This function must not be used in interrupt context. Unlocking |
| 451 | * of a unlocked mutex is not allowed. |
| 452 | */ |
| 453 | void __sched ww_mutex_unlock(struct ww_mutex *lock) |
| 454 | { |
| 455 | /* |
| 456 | * The unlocking fastpath is the 0->1 transition from 'locked' |
| 457 | * into 'unlocked' state: |
| 458 | */ |
| 459 | if (lock->ctx) { |
| 460 | #ifdef CONFIG_DEBUG_MUTEXES |
| 461 | DEBUG_LOCKS_WARN_ON(!lock->ctx->acquired); |
| 462 | #endif |
| 463 | if (lock->ctx->acquired > 0) |
| 464 | lock->ctx->acquired--; |
| 465 | lock->ctx = NULL; |
| 466 | } |
| 467 | |
| 468 | #ifndef CONFIG_DEBUG_MUTEXES |
| 469 | /* |
| 470 | * When debugging is enabled we must not clear the owner before time, |
| 471 | * the slow path will always be taken, and that clears the owner field |
| 472 | * after verifying that it was indeed current. |
| 473 | */ |
| 474 | mutex_clear_owner(&lock->base); |
| 475 | #endif |
| 476 | __mutex_fastpath_unlock(&lock->base.count, __mutex_unlock_slowpath); |
| 477 | } |
| 478 | EXPORT_SYMBOL(ww_mutex_unlock); |
| 479 | |
| 480 | static inline int __sched |
| 481 | __ww_mutex_lock_check_stamp(struct mutex *lock, struct ww_acquire_ctx *ctx) |
| 482 | { |
| 483 | struct ww_mutex *ww = container_of(lock, struct ww_mutex, base); |
| 484 | struct ww_acquire_ctx *hold_ctx = READ_ONCE(ww->ctx); |
| 485 | |
| 486 | if (!hold_ctx) |
| 487 | return 0; |
| 488 | |
| 489 | if (unlikely(ctx == hold_ctx)) |
| 490 | return -EALREADY; |
| 491 | |
| 492 | if (ctx->stamp - hold_ctx->stamp <= LONG_MAX && |
| 493 | (ctx->stamp != hold_ctx->stamp || ctx > hold_ctx)) { |
| 494 | #ifdef CONFIG_DEBUG_MUTEXES |
| 495 | DEBUG_LOCKS_WARN_ON(ctx->contending_lock); |
| 496 | ctx->contending_lock = ww; |
| 497 | #endif |
| 498 | return -EDEADLK; |
| 499 | } |
| 500 | |
| 501 | return 0; |
| 502 | } |
| 503 | |
| 504 | /* |
| 505 | * Lock a mutex (possibly interruptible), slowpath: |
| 506 | */ |
| 507 | static __always_inline int __sched |
| 508 | __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, |
| 509 | struct lockdep_map *nest_lock, unsigned long ip, |
| 510 | struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx) |
| 511 | { |
| 512 | struct task_struct *task = current; |
| 513 | struct mutex_waiter waiter; |
| 514 | unsigned long flags; |
| 515 | int ret; |
| 516 | |
| 517 | preempt_disable(); |
| 518 | mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip); |
| 519 | |
| 520 | if (mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx)) { |
| 521 | /* got the lock, yay! */ |
| 522 | preempt_enable(); |
| 523 | return 0; |
| 524 | } |
| 525 | |
| 526 | spin_lock_mutex(&lock->wait_lock, flags); |
| 527 | |
| 528 | /* |
| 529 | * Once more, try to acquire the lock. Only try-lock the mutex if |
| 530 | * it is unlocked to reduce unnecessary xchg() operations. |
| 531 | */ |
| 532 | if (!mutex_is_locked(lock) && |
| 533 | (atomic_xchg_acquire(&lock->count, 0) == 1)) |
| 534 | goto skip_wait; |
| 535 | |
| 536 | debug_mutex_lock_common(lock, &waiter); |
| 537 | debug_mutex_add_waiter(lock, &waiter, task_thread_info(task)); |
| 538 | |
| 539 | /* add waiting tasks to the end of the waitqueue (FIFO): */ |
| 540 | list_add_tail(&waiter.list, &lock->wait_list); |
| 541 | waiter.task = task; |
| 542 | |
| 543 | lock_contended(&lock->dep_map, ip); |
| 544 | |
| 545 | for (;;) { |
| 546 | /* |
| 547 | * Lets try to take the lock again - this is needed even if |
| 548 | * we get here for the first time (shortly after failing to |
| 549 | * acquire the lock), to make sure that we get a wakeup once |
| 550 | * it's unlocked. Later on, if we sleep, this is the |
| 551 | * operation that gives us the lock. We xchg it to -1, so |
| 552 | * that when we release the lock, we properly wake up the |
| 553 | * other waiters. We only attempt the xchg if the count is |
| 554 | * non-negative in order to avoid unnecessary xchg operations: |
| 555 | */ |
| 556 | if (atomic_read(&lock->count) >= 0 && |
| 557 | (atomic_xchg_acquire(&lock->count, -1) == 1)) |
| 558 | break; |
| 559 | |
| 560 | /* |
| 561 | * got a signal? (This code gets eliminated in the |
| 562 | * TASK_UNINTERRUPTIBLE case.) |
| 563 | */ |
| 564 | if (unlikely(signal_pending_state(state, task))) { |
| 565 | ret = -EINTR; |
| 566 | goto err; |
| 567 | } |
| 568 | |
| 569 | if (use_ww_ctx && ww_ctx->acquired > 0) { |
| 570 | ret = __ww_mutex_lock_check_stamp(lock, ww_ctx); |
| 571 | if (ret) |
| 572 | goto err; |
| 573 | } |
| 574 | |
| 575 | __set_task_state(task, state); |
| 576 | |
| 577 | /* didn't get the lock, go to sleep: */ |
| 578 | spin_unlock_mutex(&lock->wait_lock, flags); |
| 579 | schedule_preempt_disabled(); |
| 580 | spin_lock_mutex(&lock->wait_lock, flags); |
| 581 | } |
| 582 | __set_task_state(task, TASK_RUNNING); |
| 583 | |
| 584 | mutex_remove_waiter(lock, &waiter, current_thread_info()); |
| 585 | /* set it to 0 if there are no waiters left: */ |
| 586 | if (likely(list_empty(&lock->wait_list))) |
| 587 | atomic_set(&lock->count, 0); |
| 588 | debug_mutex_free_waiter(&waiter); |
| 589 | |
| 590 | skip_wait: |
| 591 | /* got the lock - cleanup and rejoice! */ |
| 592 | lock_acquired(&lock->dep_map, ip); |
| 593 | mutex_set_owner(lock); |
| 594 | |
| 595 | if (use_ww_ctx) { |
| 596 | struct ww_mutex *ww = container_of(lock, struct ww_mutex, base); |
| 597 | ww_mutex_set_context_slowpath(ww, ww_ctx); |
| 598 | } |
| 599 | |
| 600 | spin_unlock_mutex(&lock->wait_lock, flags); |
| 601 | preempt_enable(); |
| 602 | return 0; |
| 603 | |
| 604 | err: |
| 605 | mutex_remove_waiter(lock, &waiter, task_thread_info(task)); |
| 606 | spin_unlock_mutex(&lock->wait_lock, flags); |
| 607 | debug_mutex_free_waiter(&waiter); |
| 608 | mutex_release(&lock->dep_map, 1, ip); |
| 609 | preempt_enable(); |
| 610 | return ret; |
| 611 | } |
| 612 | |
| 613 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
| 614 | void __sched |
| 615 | mutex_lock_nested(struct mutex *lock, unsigned int subclass) |
| 616 | { |
| 617 | might_sleep(); |
| 618 | __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, |
| 619 | subclass, NULL, _RET_IP_, NULL, 0); |
| 620 | } |
| 621 | |
| 622 | EXPORT_SYMBOL_GPL(mutex_lock_nested); |
| 623 | |
| 624 | void __sched |
| 625 | _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest) |
| 626 | { |
| 627 | might_sleep(); |
| 628 | __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, |
| 629 | 0, nest, _RET_IP_, NULL, 0); |
| 630 | } |
| 631 | |
| 632 | EXPORT_SYMBOL_GPL(_mutex_lock_nest_lock); |
| 633 | |
| 634 | int __sched |
| 635 | mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass) |
| 636 | { |
| 637 | might_sleep(); |
| 638 | return __mutex_lock_common(lock, TASK_KILLABLE, |
| 639 | subclass, NULL, _RET_IP_, NULL, 0); |
| 640 | } |
| 641 | EXPORT_SYMBOL_GPL(mutex_lock_killable_nested); |
| 642 | |
| 643 | int __sched |
| 644 | mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass) |
| 645 | { |
| 646 | might_sleep(); |
| 647 | return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, |
| 648 | subclass, NULL, _RET_IP_, NULL, 0); |
| 649 | } |
| 650 | |
| 651 | EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested); |
| 652 | |
| 653 | static inline int |
| 654 | ww_mutex_deadlock_injection(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) |
| 655 | { |
| 656 | #ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH |
| 657 | unsigned tmp; |
| 658 | |
| 659 | if (ctx->deadlock_inject_countdown-- == 0) { |
| 660 | tmp = ctx->deadlock_inject_interval; |
| 661 | if (tmp > UINT_MAX/4) |
| 662 | tmp = UINT_MAX; |
| 663 | else |
| 664 | tmp = tmp*2 + tmp + tmp/2; |
| 665 | |
| 666 | ctx->deadlock_inject_interval = tmp; |
| 667 | ctx->deadlock_inject_countdown = tmp; |
| 668 | ctx->contending_lock = lock; |
| 669 | |
| 670 | ww_mutex_unlock(lock); |
| 671 | |
| 672 | return -EDEADLK; |
| 673 | } |
| 674 | #endif |
| 675 | |
| 676 | return 0; |
| 677 | } |
| 678 | |
| 679 | int __sched |
| 680 | __ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) |
| 681 | { |
| 682 | int ret; |
| 683 | |
| 684 | might_sleep(); |
| 685 | ret = __mutex_lock_common(&lock->base, TASK_UNINTERRUPTIBLE, |
| 686 | 0, &ctx->dep_map, _RET_IP_, ctx, 1); |
| 687 | if (!ret && ctx->acquired > 1) |
| 688 | return ww_mutex_deadlock_injection(lock, ctx); |
| 689 | |
| 690 | return ret; |
| 691 | } |
| 692 | EXPORT_SYMBOL_GPL(__ww_mutex_lock); |
| 693 | |
| 694 | int __sched |
| 695 | __ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) |
| 696 | { |
| 697 | int ret; |
| 698 | |
| 699 | might_sleep(); |
| 700 | ret = __mutex_lock_common(&lock->base, TASK_INTERRUPTIBLE, |
| 701 | 0, &ctx->dep_map, _RET_IP_, ctx, 1); |
| 702 | |
| 703 | if (!ret && ctx->acquired > 1) |
| 704 | return ww_mutex_deadlock_injection(lock, ctx); |
| 705 | |
| 706 | return ret; |
| 707 | } |
| 708 | EXPORT_SYMBOL_GPL(__ww_mutex_lock_interruptible); |
| 709 | |
| 710 | #endif |
| 711 | |
| 712 | /* |
| 713 | * Release the lock, slowpath: |
| 714 | */ |
| 715 | static inline void |
| 716 | __mutex_unlock_common_slowpath(struct mutex *lock, int nested) |
| 717 | { |
| 718 | unsigned long flags; |
| 719 | WAKE_Q(wake_q); |
| 720 | |
| 721 | /* |
| 722 | * As a performance measurement, release the lock before doing other |
| 723 | * wakeup related duties to follow. This allows other tasks to acquire |
| 724 | * the lock sooner, while still handling cleanups in past unlock calls. |
| 725 | * This can be done as we do not enforce strict equivalence between the |
| 726 | * mutex counter and wait_list. |
| 727 | * |
| 728 | * |
| 729 | * Some architectures leave the lock unlocked in the fastpath failure |
| 730 | * case, others need to leave it locked. In the later case we have to |
| 731 | * unlock it here - as the lock counter is currently 0 or negative. |
| 732 | */ |
| 733 | if (__mutex_slowpath_needs_to_unlock()) |
| 734 | atomic_set(&lock->count, 1); |
| 735 | |
| 736 | spin_lock_mutex(&lock->wait_lock, flags); |
| 737 | mutex_release(&lock->dep_map, nested, _RET_IP_); |
| 738 | debug_mutex_unlock(lock); |
| 739 | |
| 740 | if (!list_empty(&lock->wait_list)) { |
| 741 | /* get the first entry from the wait-list: */ |
| 742 | struct mutex_waiter *waiter = |
| 743 | list_entry(lock->wait_list.next, |
| 744 | struct mutex_waiter, list); |
| 745 | |
| 746 | debug_mutex_wake_waiter(lock, waiter); |
| 747 | wake_q_add(&wake_q, waiter->task); |
| 748 | } |
| 749 | |
| 750 | spin_unlock_mutex(&lock->wait_lock, flags); |
| 751 | wake_up_q(&wake_q); |
| 752 | } |
| 753 | |
| 754 | /* |
| 755 | * Release the lock, slowpath: |
| 756 | */ |
| 757 | __visible void |
| 758 | __mutex_unlock_slowpath(atomic_t *lock_count) |
| 759 | { |
| 760 | struct mutex *lock = container_of(lock_count, struct mutex, count); |
| 761 | |
| 762 | __mutex_unlock_common_slowpath(lock, 1); |
| 763 | } |
| 764 | |
| 765 | #ifndef CONFIG_DEBUG_LOCK_ALLOC |
| 766 | /* |
| 767 | * Here come the less common (and hence less performance-critical) APIs: |
| 768 | * mutex_lock_interruptible() and mutex_trylock(). |
| 769 | */ |
| 770 | static noinline int __sched |
| 771 | __mutex_lock_killable_slowpath(struct mutex *lock); |
| 772 | |
| 773 | static noinline int __sched |
| 774 | __mutex_lock_interruptible_slowpath(struct mutex *lock); |
| 775 | |
| 776 | /** |
| 777 | * mutex_lock_interruptible - acquire the mutex, interruptible |
| 778 | * @lock: the mutex to be acquired |
| 779 | * |
| 780 | * Lock the mutex like mutex_lock(), and return 0 if the mutex has |
| 781 | * been acquired or sleep until the mutex becomes available. If a |
| 782 | * signal arrives while waiting for the lock then this function |
| 783 | * returns -EINTR. |
| 784 | * |
| 785 | * This function is similar to (but not equivalent to) down_interruptible(). |
| 786 | */ |
| 787 | int __sched mutex_lock_interruptible(struct mutex *lock) |
| 788 | { |
| 789 | int ret; |
| 790 | |
| 791 | might_sleep(); |
| 792 | ret = __mutex_fastpath_lock_retval(&lock->count); |
| 793 | if (likely(!ret)) { |
| 794 | mutex_set_owner(lock); |
| 795 | return 0; |
| 796 | } else |
| 797 | return __mutex_lock_interruptible_slowpath(lock); |
| 798 | } |
| 799 | |
| 800 | EXPORT_SYMBOL(mutex_lock_interruptible); |
| 801 | |
| 802 | int __sched mutex_lock_killable(struct mutex *lock) |
| 803 | { |
| 804 | int ret; |
| 805 | |
| 806 | might_sleep(); |
| 807 | ret = __mutex_fastpath_lock_retval(&lock->count); |
| 808 | if (likely(!ret)) { |
| 809 | mutex_set_owner(lock); |
| 810 | return 0; |
| 811 | } else |
| 812 | return __mutex_lock_killable_slowpath(lock); |
| 813 | } |
| 814 | EXPORT_SYMBOL(mutex_lock_killable); |
| 815 | |
| 816 | __visible void __sched |
| 817 | __mutex_lock_slowpath(atomic_t *lock_count) |
| 818 | { |
| 819 | struct mutex *lock = container_of(lock_count, struct mutex, count); |
| 820 | |
| 821 | __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0, |
| 822 | NULL, _RET_IP_, NULL, 0); |
| 823 | } |
| 824 | |
| 825 | static noinline int __sched |
| 826 | __mutex_lock_killable_slowpath(struct mutex *lock) |
| 827 | { |
| 828 | return __mutex_lock_common(lock, TASK_KILLABLE, 0, |
| 829 | NULL, _RET_IP_, NULL, 0); |
| 830 | } |
| 831 | |
| 832 | static noinline int __sched |
| 833 | __mutex_lock_interruptible_slowpath(struct mutex *lock) |
| 834 | { |
| 835 | return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, 0, |
| 836 | NULL, _RET_IP_, NULL, 0); |
| 837 | } |
| 838 | |
| 839 | static noinline int __sched |
| 840 | __ww_mutex_lock_slowpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) |
| 841 | { |
| 842 | return __mutex_lock_common(&lock->base, TASK_UNINTERRUPTIBLE, 0, |
| 843 | NULL, _RET_IP_, ctx, 1); |
| 844 | } |
| 845 | |
| 846 | static noinline int __sched |
| 847 | __ww_mutex_lock_interruptible_slowpath(struct ww_mutex *lock, |
| 848 | struct ww_acquire_ctx *ctx) |
| 849 | { |
| 850 | return __mutex_lock_common(&lock->base, TASK_INTERRUPTIBLE, 0, |
| 851 | NULL, _RET_IP_, ctx, 1); |
| 852 | } |
| 853 | |
| 854 | #endif |
| 855 | |
| 856 | /* |
| 857 | * Spinlock based trylock, we take the spinlock and check whether we |
| 858 | * can get the lock: |
| 859 | */ |
| 860 | static inline int __mutex_trylock_slowpath(atomic_t *lock_count) |
| 861 | { |
| 862 | struct mutex *lock = container_of(lock_count, struct mutex, count); |
| 863 | unsigned long flags; |
| 864 | int prev; |
| 865 | |
| 866 | /* No need to trylock if the mutex is locked. */ |
| 867 | if (mutex_is_locked(lock)) |
| 868 | return 0; |
| 869 | |
| 870 | spin_lock_mutex(&lock->wait_lock, flags); |
| 871 | |
| 872 | prev = atomic_xchg_acquire(&lock->count, -1); |
| 873 | if (likely(prev == 1)) { |
| 874 | mutex_set_owner(lock); |
| 875 | mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_); |
| 876 | } |
| 877 | |
| 878 | /* Set it back to 0 if there are no waiters: */ |
| 879 | if (likely(list_empty(&lock->wait_list))) |
| 880 | atomic_set(&lock->count, 0); |
| 881 | |
| 882 | spin_unlock_mutex(&lock->wait_lock, flags); |
| 883 | |
| 884 | return prev == 1; |
| 885 | } |
| 886 | |
| 887 | /** |
| 888 | * mutex_trylock - try to acquire the mutex, without waiting |
| 889 | * @lock: the mutex to be acquired |
| 890 | * |
| 891 | * Try to acquire the mutex atomically. Returns 1 if the mutex |
| 892 | * has been acquired successfully, and 0 on contention. |
| 893 | * |
| 894 | * NOTE: this function follows the spin_trylock() convention, so |
| 895 | * it is negated from the down_trylock() return values! Be careful |
| 896 | * about this when converting semaphore users to mutexes. |
| 897 | * |
| 898 | * This function must not be used in interrupt context. The |
| 899 | * mutex must be released by the same task that acquired it. |
| 900 | */ |
| 901 | int __sched mutex_trylock(struct mutex *lock) |
| 902 | { |
| 903 | int ret; |
| 904 | |
| 905 | ret = __mutex_fastpath_trylock(&lock->count, __mutex_trylock_slowpath); |
| 906 | if (ret) |
| 907 | mutex_set_owner(lock); |
| 908 | |
| 909 | return ret; |
| 910 | } |
| 911 | EXPORT_SYMBOL(mutex_trylock); |
| 912 | |
| 913 | #ifndef CONFIG_DEBUG_LOCK_ALLOC |
| 914 | int __sched |
| 915 | __ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) |
| 916 | { |
| 917 | int ret; |
| 918 | |
| 919 | might_sleep(); |
| 920 | |
| 921 | ret = __mutex_fastpath_lock_retval(&lock->base.count); |
| 922 | |
| 923 | if (likely(!ret)) { |
| 924 | ww_mutex_set_context_fastpath(lock, ctx); |
| 925 | mutex_set_owner(&lock->base); |
| 926 | } else |
| 927 | ret = __ww_mutex_lock_slowpath(lock, ctx); |
| 928 | return ret; |
| 929 | } |
| 930 | EXPORT_SYMBOL(__ww_mutex_lock); |
| 931 | |
| 932 | int __sched |
| 933 | __ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) |
| 934 | { |
| 935 | int ret; |
| 936 | |
| 937 | might_sleep(); |
| 938 | |
| 939 | ret = __mutex_fastpath_lock_retval(&lock->base.count); |
| 940 | |
| 941 | if (likely(!ret)) { |
| 942 | ww_mutex_set_context_fastpath(lock, ctx); |
| 943 | mutex_set_owner(&lock->base); |
| 944 | } else |
| 945 | ret = __ww_mutex_lock_interruptible_slowpath(lock, ctx); |
| 946 | return ret; |
| 947 | } |
| 948 | EXPORT_SYMBOL(__ww_mutex_lock_interruptible); |
| 949 | |
| 950 | #endif |
| 951 | |
| 952 | /** |
| 953 | * atomic_dec_and_mutex_lock - return holding mutex if we dec to 0 |
| 954 | * @cnt: the atomic which we are to dec |
| 955 | * @lock: the mutex to return holding if we dec to 0 |
| 956 | * |
| 957 | * return true and hold lock if we dec to 0, return false otherwise |
| 958 | */ |
| 959 | int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock) |
| 960 | { |
| 961 | /* dec if we can't possibly hit 0 */ |
| 962 | if (atomic_add_unless(cnt, -1, 1)) |
| 963 | return 0; |
| 964 | /* we might hit 0, so take the lock */ |
| 965 | mutex_lock(lock); |
| 966 | if (!atomic_dec_and_test(cnt)) { |
| 967 | /* when we actually did the dec, we didn't hit 0 */ |
| 968 | mutex_unlock(lock); |
| 969 | return 0; |
| 970 | } |
| 971 | /* we hit 0, and we hold the lock */ |
| 972 | return 1; |
| 973 | } |
| 974 | EXPORT_SYMBOL(atomic_dec_and_mutex_lock); |