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 "mcs_spinlock.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 mutex 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 #ifdef CONFIG_MUTEX_SPIN_ON_OWNER 196 /* 197 * In order to avoid a stampede of mutex spinners from acquiring the mutex 198 * more or less simultaneously, the spinners need to acquire a MCS lock 199 * first before spinning on the owner field. 200 * 201 */ 202 203 /* 204 * Mutex spinning code migrated from kernel/sched/core.c 205 */ 206 207 static inline bool owner_running(struct mutex *lock, struct task_struct *owner) 208 { 209 if (lock->owner != owner) 210 return false; 211 212 /* 213 * Ensure we emit the owner->on_cpu, dereference _after_ checking 214 * lock->owner still matches owner, if that fails, owner might 215 * point to free()d memory, if it still matches, the rcu_read_lock() 216 * ensures the memory stays valid. 217 */ 218 barrier(); 219 220 return owner->on_cpu; 221 } 222 223 /* 224 * Look out! "owner" is an entirely speculative pointer 225 * access and not reliable. 226 */ 227 static noinline 228 int mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner) 229 { 230 rcu_read_lock(); 231 while (owner_running(lock, owner)) { 232 if (need_resched()) 233 break; 234 235 cpu_relax_lowlatency(); 236 } 237 rcu_read_unlock(); 238 239 /* 240 * We break out the loop above on need_resched() and when the 241 * owner changed, which is a sign for heavy contention. Return 242 * success only when lock->owner is NULL. 243 */ 244 return lock->owner == NULL; 245 } 246 247 /* 248 * Initial check for entering the mutex spinning loop 249 */ 250 static inline int mutex_can_spin_on_owner(struct mutex *lock) 251 { 252 struct task_struct *owner; 253 int retval = 1; 254 255 if (need_resched()) 256 return 0; 257 258 rcu_read_lock(); 259 owner = ACCESS_ONCE(lock->owner); 260 if (owner) 261 retval = owner->on_cpu; 262 rcu_read_unlock(); 263 /* 264 * if lock->owner is not set, the mutex owner may have just acquired 265 * it and not set the owner yet or the mutex has been released. 266 */ 267 return retval; 268 } 269 270 /* 271 * Atomically try to take the lock when it is available 272 */ 273 static inline bool mutex_try_to_acquire(struct mutex *lock) 274 { 275 return !mutex_is_locked(lock) && 276 (atomic_cmpxchg(&lock->count, 1, 0) == 1); 277 } 278 279 /* 280 * Optimistic spinning. 281 * 282 * We try to spin for acquisition when we find that the lock owner 283 * is currently running on a (different) CPU and while we don't 284 * need to reschedule. The rationale is that if the lock owner is 285 * running, it is likely to release the lock soon. 286 * 287 * Since this needs the lock owner, and this mutex implementation 288 * doesn't track the owner atomically in the lock field, we need to 289 * track it non-atomically. 290 * 291 * We can't do this for DEBUG_MUTEXES because that relies on wait_lock 292 * to serialize everything. 293 * 294 * The mutex spinners are queued up using MCS lock so that only one 295 * spinner can compete for the mutex. However, if mutex spinning isn't 296 * going to happen, there is no point in going through the lock/unlock 297 * overhead. 298 * 299 * Returns true when the lock was taken, otherwise false, indicating 300 * that we need to jump to the slowpath and sleep. 301 */ 302 static bool mutex_optimistic_spin(struct mutex *lock, 303 struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx) 304 { 305 struct task_struct *task = current; 306 307 if (!mutex_can_spin_on_owner(lock)) 308 goto done; 309 310 if (!osq_lock(&lock->osq)) 311 goto done; 312 313 while (true) { 314 struct task_struct *owner; 315 316 if (use_ww_ctx && ww_ctx->acquired > 0) { 317 struct ww_mutex *ww; 318 319 ww = container_of(lock, struct ww_mutex, base); 320 /* 321 * If ww->ctx is set the contents are undefined, only 322 * by acquiring wait_lock there is a guarantee that 323 * they are not invalid when reading. 324 * 325 * As such, when deadlock detection needs to be 326 * performed the optimistic spinning cannot be done. 327 */ 328 if (ACCESS_ONCE(ww->ctx)) 329 break; 330 } 331 332 /* 333 * If there's an owner, wait for it to either 334 * release the lock or go to sleep. 335 */ 336 owner = ACCESS_ONCE(lock->owner); 337 if (owner && !mutex_spin_on_owner(lock, owner)) 338 break; 339 340 /* Try to acquire the mutex if it is unlocked. */ 341 if (mutex_try_to_acquire(lock)) { 342 lock_acquired(&lock->dep_map, ip); 343 344 if (use_ww_ctx) { 345 struct ww_mutex *ww; 346 ww = container_of(lock, struct ww_mutex, base); 347 348 ww_mutex_set_context_fastpath(ww, ww_ctx); 349 } 350 351 mutex_set_owner(lock); 352 osq_unlock(&lock->osq); 353 return true; 354 } 355 356 /* 357 * When there's no owner, we might have preempted between the 358 * owner acquiring the lock and setting the owner field. If 359 * we're an RT task that will live-lock because we won't let 360 * the owner complete. 361 */ 362 if (!owner && (need_resched() || rt_task(task))) 363 break; 364 365 /* 366 * The cpu_relax() call is a compiler barrier which forces 367 * everything in this loop to be re-loaded. We don't need 368 * memory barriers as we'll eventually observe the right 369 * values at the cost of a few extra spins. 370 */ 371 cpu_relax_lowlatency(); 372 } 373 374 osq_unlock(&lock->osq); 375 done: 376 /* 377 * If we fell out of the spin path because of need_resched(), 378 * reschedule now, before we try-lock the mutex. This avoids getting 379 * scheduled out right after we obtained the mutex. 380 */ 381 if (need_resched()) 382 schedule_preempt_disabled(); 383 384 return false; 385 } 386 #else 387 static bool mutex_optimistic_spin(struct mutex *lock, 388 struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx) 389 { 390 return false; 391 } 392 #endif 393 394 __visible __used noinline 395 void __sched __mutex_unlock_slowpath(atomic_t *lock_count); 396 397 /** 398 * mutex_unlock - release the mutex 399 * @lock: the mutex to be released 400 * 401 * Unlock a mutex that has been locked by this task previously. 402 * 403 * This function must not be used in interrupt context. Unlocking 404 * of a not locked mutex is not allowed. 405 * 406 * This function is similar to (but not equivalent to) up(). 407 */ 408 void __sched mutex_unlock(struct mutex *lock) 409 { 410 /* 411 * The unlocking fastpath is the 0->1 transition from 'locked' 412 * into 'unlocked' state: 413 */ 414 #ifndef CONFIG_DEBUG_MUTEXES 415 /* 416 * When debugging is enabled we must not clear the owner before time, 417 * the slow path will always be taken, and that clears the owner field 418 * after verifying that it was indeed current. 419 */ 420 mutex_clear_owner(lock); 421 #endif 422 __mutex_fastpath_unlock(&lock->count, __mutex_unlock_slowpath); 423 } 424 425 EXPORT_SYMBOL(mutex_unlock); 426 427 /** 428 * ww_mutex_unlock - release the w/w mutex 429 * @lock: the mutex to be released 430 * 431 * Unlock a mutex that has been locked by this task previously with any of the 432 * ww_mutex_lock* functions (with or without an acquire context). It is 433 * forbidden to release the locks after releasing the acquire context. 434 * 435 * This function must not be used in interrupt context. Unlocking 436 * of a unlocked mutex is not allowed. 437 */ 438 void __sched ww_mutex_unlock(struct ww_mutex *lock) 439 { 440 /* 441 * The unlocking fastpath is the 0->1 transition from 'locked' 442 * into 'unlocked' state: 443 */ 444 if (lock->ctx) { 445 #ifdef CONFIG_DEBUG_MUTEXES 446 DEBUG_LOCKS_WARN_ON(!lock->ctx->acquired); 447 #endif 448 if (lock->ctx->acquired > 0) 449 lock->ctx->acquired--; 450 lock->ctx = NULL; 451 } 452 453 #ifndef CONFIG_DEBUG_MUTEXES 454 /* 455 * When debugging is enabled we must not clear the owner before time, 456 * the slow path will always be taken, and that clears the owner field 457 * after verifying that it was indeed current. 458 */ 459 mutex_clear_owner(&lock->base); 460 #endif 461 __mutex_fastpath_unlock(&lock->base.count, __mutex_unlock_slowpath); 462 } 463 EXPORT_SYMBOL(ww_mutex_unlock); 464 465 static inline int __sched 466 __mutex_lock_check_stamp(struct mutex *lock, struct ww_acquire_ctx *ctx) 467 { 468 struct ww_mutex *ww = container_of(lock, struct ww_mutex, base); 469 struct ww_acquire_ctx *hold_ctx = ACCESS_ONCE(ww->ctx); 470 471 if (!hold_ctx) 472 return 0; 473 474 if (unlikely(ctx == hold_ctx)) 475 return -EALREADY; 476 477 if (ctx->stamp - hold_ctx->stamp <= LONG_MAX && 478 (ctx->stamp != hold_ctx->stamp || ctx > hold_ctx)) { 479 #ifdef CONFIG_DEBUG_MUTEXES 480 DEBUG_LOCKS_WARN_ON(ctx->contending_lock); 481 ctx->contending_lock = ww; 482 #endif 483 return -EDEADLK; 484 } 485 486 return 0; 487 } 488 489 /* 490 * Lock a mutex (possibly interruptible), slowpath: 491 */ 492 static __always_inline int __sched 493 __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, 494 struct lockdep_map *nest_lock, unsigned long ip, 495 struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx) 496 { 497 struct task_struct *task = current; 498 struct mutex_waiter waiter; 499 unsigned long flags; 500 int ret; 501 502 preempt_disable(); 503 mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip); 504 505 if (mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx)) { 506 /* got the lock, yay! */ 507 preempt_enable(); 508 return 0; 509 } 510 511 spin_lock_mutex(&lock->wait_lock, flags); 512 513 /* 514 * Once more, try to acquire the lock. Only try-lock the mutex if 515 * it is unlocked to reduce unnecessary xchg() operations. 516 */ 517 if (!mutex_is_locked(lock) && (atomic_xchg(&lock->count, 0) == 1)) 518 goto skip_wait; 519 520 debug_mutex_lock_common(lock, &waiter); 521 debug_mutex_add_waiter(lock, &waiter, task_thread_info(task)); 522 523 /* add waiting tasks to the end of the waitqueue (FIFO): */ 524 list_add_tail(&waiter.list, &lock->wait_list); 525 waiter.task = task; 526 527 lock_contended(&lock->dep_map, ip); 528 529 for (;;) { 530 /* 531 * Lets try to take the lock again - this is needed even if 532 * we get here for the first time (shortly after failing to 533 * acquire the lock), to make sure that we get a wakeup once 534 * it's unlocked. Later on, if we sleep, this is the 535 * operation that gives us the lock. We xchg it to -1, so 536 * that when we release the lock, we properly wake up the 537 * other waiters. We only attempt the xchg if the count is 538 * non-negative in order to avoid unnecessary xchg operations: 539 */ 540 if (atomic_read(&lock->count) >= 0 && 541 (atomic_xchg(&lock->count, -1) == 1)) 542 break; 543 544 /* 545 * got a signal? (This code gets eliminated in the 546 * TASK_UNINTERRUPTIBLE case.) 547 */ 548 if (unlikely(signal_pending_state(state, task))) { 549 ret = -EINTR; 550 goto err; 551 } 552 553 if (use_ww_ctx && ww_ctx->acquired > 0) { 554 ret = __mutex_lock_check_stamp(lock, ww_ctx); 555 if (ret) 556 goto err; 557 } 558 559 __set_task_state(task, state); 560 561 /* didn't get the lock, go to sleep: */ 562 spin_unlock_mutex(&lock->wait_lock, flags); 563 schedule_preempt_disabled(); 564 spin_lock_mutex(&lock->wait_lock, flags); 565 } 566 mutex_remove_waiter(lock, &waiter, current_thread_info()); 567 /* set it to 0 if there are no waiters left: */ 568 if (likely(list_empty(&lock->wait_list))) 569 atomic_set(&lock->count, 0); 570 debug_mutex_free_waiter(&waiter); 571 572 skip_wait: 573 /* got the lock - cleanup and rejoice! */ 574 lock_acquired(&lock->dep_map, ip); 575 mutex_set_owner(lock); 576 577 if (use_ww_ctx) { 578 struct ww_mutex *ww = container_of(lock, struct ww_mutex, base); 579 struct mutex_waiter *cur; 580 581 /* 582 * This branch gets optimized out for the common case, 583 * and is only important for ww_mutex_lock. 584 */ 585 ww_mutex_lock_acquired(ww, ww_ctx); 586 ww->ctx = ww_ctx; 587 588 /* 589 * Give any possible sleeping processes the chance to wake up, 590 * so they can recheck if they have to back off. 591 */ 592 list_for_each_entry(cur, &lock->wait_list, list) { 593 debug_mutex_wake_waiter(lock, cur); 594 wake_up_process(cur->task); 595 } 596 } 597 598 spin_unlock_mutex(&lock->wait_lock, flags); 599 preempt_enable(); 600 return 0; 601 602 err: 603 mutex_remove_waiter(lock, &waiter, task_thread_info(task)); 604 spin_unlock_mutex(&lock->wait_lock, flags); 605 debug_mutex_free_waiter(&waiter); 606 mutex_release(&lock->dep_map, 1, ip); 607 preempt_enable(); 608 return ret; 609 } 610 611 #ifdef CONFIG_DEBUG_LOCK_ALLOC 612 void __sched 613 mutex_lock_nested(struct mutex *lock, unsigned int subclass) 614 { 615 might_sleep(); 616 __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 617 subclass, NULL, _RET_IP_, NULL, 0); 618 } 619 620 EXPORT_SYMBOL_GPL(mutex_lock_nested); 621 622 void __sched 623 _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest) 624 { 625 might_sleep(); 626 __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 627 0, nest, _RET_IP_, NULL, 0); 628 } 629 630 EXPORT_SYMBOL_GPL(_mutex_lock_nest_lock); 631 632 int __sched 633 mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass) 634 { 635 might_sleep(); 636 return __mutex_lock_common(lock, TASK_KILLABLE, 637 subclass, NULL, _RET_IP_, NULL, 0); 638 } 639 EXPORT_SYMBOL_GPL(mutex_lock_killable_nested); 640 641 int __sched 642 mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass) 643 { 644 might_sleep(); 645 return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, 646 subclass, NULL, _RET_IP_, NULL, 0); 647 } 648 649 EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested); 650 651 static inline int 652 ww_mutex_deadlock_injection(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) 653 { 654 #ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH 655 unsigned tmp; 656 657 if (ctx->deadlock_inject_countdown-- == 0) { 658 tmp = ctx->deadlock_inject_interval; 659 if (tmp > UINT_MAX/4) 660 tmp = UINT_MAX; 661 else 662 tmp = tmp*2 + tmp + tmp/2; 663 664 ctx->deadlock_inject_interval = tmp; 665 ctx->deadlock_inject_countdown = tmp; 666 ctx->contending_lock = lock; 667 668 ww_mutex_unlock(lock); 669 670 return -EDEADLK; 671 } 672 #endif 673 674 return 0; 675 } 676 677 int __sched 678 __ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) 679 { 680 int ret; 681 682 might_sleep(); 683 ret = __mutex_lock_common(&lock->base, TASK_UNINTERRUPTIBLE, 684 0, &ctx->dep_map, _RET_IP_, ctx, 1); 685 if (!ret && ctx->acquired > 1) 686 return ww_mutex_deadlock_injection(lock, ctx); 687 688 return ret; 689 } 690 EXPORT_SYMBOL_GPL(__ww_mutex_lock); 691 692 int __sched 693 __ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) 694 { 695 int ret; 696 697 might_sleep(); 698 ret = __mutex_lock_common(&lock->base, TASK_INTERRUPTIBLE, 699 0, &ctx->dep_map, _RET_IP_, ctx, 1); 700 701 if (!ret && ctx->acquired > 1) 702 return ww_mutex_deadlock_injection(lock, ctx); 703 704 return ret; 705 } 706 EXPORT_SYMBOL_GPL(__ww_mutex_lock_interruptible); 707 708 #endif 709 710 /* 711 * Release the lock, slowpath: 712 */ 713 static inline void 714 __mutex_unlock_common_slowpath(struct mutex *lock, int nested) 715 { 716 unsigned long flags; 717 718 /* 719 * As a performance measurement, release the lock before doing other 720 * wakeup related duties to follow. This allows other tasks to acquire 721 * the lock sooner, while still handling cleanups in past unlock calls. 722 * This can be done as we do not enforce strict equivalence between the 723 * mutex counter and wait_list. 724 * 725 * 726 * Some architectures leave the lock unlocked in the fastpath failure 727 * case, others need to leave it locked. In the later case we have to 728 * unlock it here - as the lock counter is currently 0 or negative. 729 */ 730 if (__mutex_slowpath_needs_to_unlock()) 731 atomic_set(&lock->count, 1); 732 733 spin_lock_mutex(&lock->wait_lock, flags); 734 mutex_release(&lock->dep_map, nested, _RET_IP_); 735 debug_mutex_unlock(lock); 736 737 if (!list_empty(&lock->wait_list)) { 738 /* get the first entry from the wait-list: */ 739 struct mutex_waiter *waiter = 740 list_entry(lock->wait_list.next, 741 struct mutex_waiter, list); 742 743 debug_mutex_wake_waiter(lock, waiter); 744 745 wake_up_process(waiter->task); 746 } 747 748 spin_unlock_mutex(&lock->wait_lock, flags); 749 } 750 751 /* 752 * Release the lock, slowpath: 753 */ 754 __visible void 755 __mutex_unlock_slowpath(atomic_t *lock_count) 756 { 757 struct mutex *lock = container_of(lock_count, struct mutex, count); 758 759 __mutex_unlock_common_slowpath(lock, 1); 760 } 761 762 #ifndef CONFIG_DEBUG_LOCK_ALLOC 763 /* 764 * Here come the less common (and hence less performance-critical) APIs: 765 * mutex_lock_interruptible() and mutex_trylock(). 766 */ 767 static noinline int __sched 768 __mutex_lock_killable_slowpath(struct mutex *lock); 769 770 static noinline int __sched 771 __mutex_lock_interruptible_slowpath(struct mutex *lock); 772 773 /** 774 * mutex_lock_interruptible - acquire the mutex, interruptible 775 * @lock: the mutex to be acquired 776 * 777 * Lock the mutex like mutex_lock(), and return 0 if the mutex has 778 * been acquired or sleep until the mutex becomes available. If a 779 * signal arrives while waiting for the lock then this function 780 * returns -EINTR. 781 * 782 * This function is similar to (but not equivalent to) down_interruptible(). 783 */ 784 int __sched mutex_lock_interruptible(struct mutex *lock) 785 { 786 int ret; 787 788 might_sleep(); 789 ret = __mutex_fastpath_lock_retval(&lock->count); 790 if (likely(!ret)) { 791 mutex_set_owner(lock); 792 return 0; 793 } else 794 return __mutex_lock_interruptible_slowpath(lock); 795 } 796 797 EXPORT_SYMBOL(mutex_lock_interruptible); 798 799 int __sched mutex_lock_killable(struct mutex *lock) 800 { 801 int ret; 802 803 might_sleep(); 804 ret = __mutex_fastpath_lock_retval(&lock->count); 805 if (likely(!ret)) { 806 mutex_set_owner(lock); 807 return 0; 808 } else 809 return __mutex_lock_killable_slowpath(lock); 810 } 811 EXPORT_SYMBOL(mutex_lock_killable); 812 813 __visible void __sched 814 __mutex_lock_slowpath(atomic_t *lock_count) 815 { 816 struct mutex *lock = container_of(lock_count, struct mutex, count); 817 818 __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0, 819 NULL, _RET_IP_, NULL, 0); 820 } 821 822 static noinline int __sched 823 __mutex_lock_killable_slowpath(struct mutex *lock) 824 { 825 return __mutex_lock_common(lock, TASK_KILLABLE, 0, 826 NULL, _RET_IP_, NULL, 0); 827 } 828 829 static noinline int __sched 830 __mutex_lock_interruptible_slowpath(struct mutex *lock) 831 { 832 return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, 0, 833 NULL, _RET_IP_, NULL, 0); 834 } 835 836 static noinline int __sched 837 __ww_mutex_lock_slowpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) 838 { 839 return __mutex_lock_common(&lock->base, TASK_UNINTERRUPTIBLE, 0, 840 NULL, _RET_IP_, ctx, 1); 841 } 842 843 static noinline int __sched 844 __ww_mutex_lock_interruptible_slowpath(struct ww_mutex *lock, 845 struct ww_acquire_ctx *ctx) 846 { 847 return __mutex_lock_common(&lock->base, TASK_INTERRUPTIBLE, 0, 848 NULL, _RET_IP_, ctx, 1); 849 } 850 851 #endif 852 853 /* 854 * Spinlock based trylock, we take the spinlock and check whether we 855 * can get the lock: 856 */ 857 static inline int __mutex_trylock_slowpath(atomic_t *lock_count) 858 { 859 struct mutex *lock = container_of(lock_count, struct mutex, count); 860 unsigned long flags; 861 int prev; 862 863 /* No need to trylock if the mutex is locked. */ 864 if (mutex_is_locked(lock)) 865 return 0; 866 867 spin_lock_mutex(&lock->wait_lock, flags); 868 869 prev = atomic_xchg(&lock->count, -1); 870 if (likely(prev == 1)) { 871 mutex_set_owner(lock); 872 mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_); 873 } 874 875 /* Set it back to 0 if there are no waiters: */ 876 if (likely(list_empty(&lock->wait_list))) 877 atomic_set(&lock->count, 0); 878 879 spin_unlock_mutex(&lock->wait_lock, flags); 880 881 return prev == 1; 882 } 883 884 /** 885 * mutex_trylock - try to acquire the mutex, without waiting 886 * @lock: the mutex to be acquired 887 * 888 * Try to acquire the mutex atomically. Returns 1 if the mutex 889 * has been acquired successfully, and 0 on contention. 890 * 891 * NOTE: this function follows the spin_trylock() convention, so 892 * it is negated from the down_trylock() return values! Be careful 893 * about this when converting semaphore users to mutexes. 894 * 895 * This function must not be used in interrupt context. The 896 * mutex must be released by the same task that acquired it. 897 */ 898 int __sched mutex_trylock(struct mutex *lock) 899 { 900 int ret; 901 902 ret = __mutex_fastpath_trylock(&lock->count, __mutex_trylock_slowpath); 903 if (ret) 904 mutex_set_owner(lock); 905 906 return ret; 907 } 908 EXPORT_SYMBOL(mutex_trylock); 909 910 #ifndef CONFIG_DEBUG_LOCK_ALLOC 911 int __sched 912 __ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) 913 { 914 int ret; 915 916 might_sleep(); 917 918 ret = __mutex_fastpath_lock_retval(&lock->base.count); 919 920 if (likely(!ret)) { 921 ww_mutex_set_context_fastpath(lock, ctx); 922 mutex_set_owner(&lock->base); 923 } else 924 ret = __ww_mutex_lock_slowpath(lock, ctx); 925 return ret; 926 } 927 EXPORT_SYMBOL(__ww_mutex_lock); 928 929 int __sched 930 __ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) 931 { 932 int ret; 933 934 might_sleep(); 935 936 ret = __mutex_fastpath_lock_retval(&lock->base.count); 937 938 if (likely(!ret)) { 939 ww_mutex_set_context_fastpath(lock, ctx); 940 mutex_set_owner(&lock->base); 941 } else 942 ret = __ww_mutex_lock_interruptible_slowpath(lock, ctx); 943 return ret; 944 } 945 EXPORT_SYMBOL(__ww_mutex_lock_interruptible); 946 947 #endif 948 949 /** 950 * atomic_dec_and_mutex_lock - return holding mutex if we dec to 0 951 * @cnt: the atomic which we are to dec 952 * @lock: the mutex to return holding if we dec to 0 953 * 954 * return true and hold lock if we dec to 0, return false otherwise 955 */ 956 int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock) 957 { 958 /* dec if we can't possibly hit 0 */ 959 if (atomic_add_unless(cnt, -1, 1)) 960 return 0; 961 /* we might hit 0, so take the lock */ 962 mutex_lock(lock); 963 if (!atomic_dec_and_test(cnt)) { 964 /* when we actually did the dec, we didn't hit 0 */ 965 mutex_unlock(lock); 966 return 0; 967 } 968 /* we hit 0, and we hold the lock */ 969 return 1; 970 } 971 EXPORT_SYMBOL(atomic_dec_and_mutex_lock); 972