| 1 | /* |
| 2 | * kernel/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/mutex-design.txt. |
| 19 | */ |
| 20 | #include <linux/mutex.h> |
| 21 | #include <linux/sched.h> |
| 22 | #include <linux/module.h> |
| 23 | #include <linux/spinlock.h> |
| 24 | #include <linux/interrupt.h> |
| 25 | #include <linux/debug_locks.h> |
| 26 | |
| 27 | /* |
| 28 | * In the DEBUG case we are using the "NULL fastpath" for mutexes, |
| 29 | * which forces all calls into the slowpath: |
| 30 | */ |
| 31 | #ifdef CONFIG_DEBUG_MUTEXES |
| 32 | # include "mutex-debug.h" |
| 33 | # include <asm-generic/mutex-null.h> |
| 34 | #else |
| 35 | # include "mutex.h" |
| 36 | # include <asm/mutex.h> |
| 37 | #endif |
| 38 | |
| 39 | /*** |
| 40 | * mutex_init - initialize the mutex |
| 41 | * @lock: the mutex to be initialized |
| 42 | * @key: the lock_class_key for the class; used by mutex lock debugging |
| 43 | * |
| 44 | * Initialize the mutex to unlocked state. |
| 45 | * |
| 46 | * It is not allowed to initialize an already locked mutex. |
| 47 | */ |
| 48 | void |
| 49 | __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key) |
| 50 | { |
| 51 | atomic_set(&lock->count, 1); |
| 52 | spin_lock_init(&lock->wait_lock); |
| 53 | INIT_LIST_HEAD(&lock->wait_list); |
| 54 | mutex_clear_owner(lock); |
| 55 | |
| 56 | debug_mutex_init(lock, name, key); |
| 57 | } |
| 58 | |
| 59 | EXPORT_SYMBOL(__mutex_init); |
| 60 | |
| 61 | #ifndef CONFIG_DEBUG_LOCK_ALLOC |
| 62 | /* |
| 63 | * We split the mutex lock/unlock logic into separate fastpath and |
| 64 | * slowpath functions, to reduce the register pressure on the fastpath. |
| 65 | * We also put the fastpath first in the kernel image, to make sure the |
| 66 | * branch is predicted by the CPU as default-untaken. |
| 67 | */ |
| 68 | static __used noinline void __sched |
| 69 | __mutex_lock_slowpath(atomic_t *lock_count); |
| 70 | |
| 71 | /*** |
| 72 | * mutex_lock - acquire the mutex |
| 73 | * @lock: the mutex to be acquired |
| 74 | * |
| 75 | * Lock the mutex exclusively for this task. If the mutex is not |
| 76 | * available right now, it will sleep until it can get it. |
| 77 | * |
| 78 | * The mutex must later on be released by the same task that |
| 79 | * acquired it. Recursive locking is not allowed. The task |
| 80 | * may not exit without first unlocking the mutex. Also, kernel |
| 81 | * memory where the mutex resides mutex must not be freed with |
| 82 | * the mutex still locked. The mutex must first be initialized |
| 83 | * (or statically defined) before it can be locked. memset()-ing |
| 84 | * the mutex to 0 is not allowed. |
| 85 | * |
| 86 | * ( The CONFIG_DEBUG_MUTEXES .config option turns on debugging |
| 87 | * checks that will enforce the restrictions and will also do |
| 88 | * deadlock debugging. ) |
| 89 | * |
| 90 | * This function is similar to (but not equivalent to) down(). |
| 91 | */ |
| 92 | void __sched mutex_lock(struct mutex *lock) |
| 93 | { |
| 94 | might_sleep(); |
| 95 | /* |
| 96 | * The locking fastpath is the 1->0 transition from |
| 97 | * 'unlocked' into 'locked' state. |
| 98 | */ |
| 99 | __mutex_fastpath_lock(&lock->count, __mutex_lock_slowpath); |
| 100 | mutex_set_owner(lock); |
| 101 | } |
| 102 | |
| 103 | EXPORT_SYMBOL(mutex_lock); |
| 104 | #endif |
| 105 | |
| 106 | static __used noinline void __sched __mutex_unlock_slowpath(atomic_t *lock_count); |
| 107 | |
| 108 | /*** |
| 109 | * mutex_unlock - release the mutex |
| 110 | * @lock: the mutex to be released |
| 111 | * |
| 112 | * Unlock a mutex that has been locked by this task previously. |
| 113 | * |
| 114 | * This function must not be used in interrupt context. Unlocking |
| 115 | * of a not locked mutex is not allowed. |
| 116 | * |
| 117 | * This function is similar to (but not equivalent to) up(). |
| 118 | */ |
| 119 | void __sched mutex_unlock(struct mutex *lock) |
| 120 | { |
| 121 | /* |
| 122 | * The unlocking fastpath is the 0->1 transition from 'locked' |
| 123 | * into 'unlocked' state: |
| 124 | */ |
| 125 | #ifndef CONFIG_DEBUG_MUTEXES |
| 126 | /* |
| 127 | * When debugging is enabled we must not clear the owner before time, |
| 128 | * the slow path will always be taken, and that clears the owner field |
| 129 | * after verifying that it was indeed current. |
| 130 | */ |
| 131 | mutex_clear_owner(lock); |
| 132 | #endif |
| 133 | __mutex_fastpath_unlock(&lock->count, __mutex_unlock_slowpath); |
| 134 | } |
| 135 | |
| 136 | EXPORT_SYMBOL(mutex_unlock); |
| 137 | |
| 138 | /* |
| 139 | * Lock a mutex (possibly interruptible), slowpath: |
| 140 | */ |
| 141 | static inline int __sched |
| 142 | __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, |
| 143 | unsigned long ip) |
| 144 | { |
| 145 | struct task_struct *task = current; |
| 146 | struct mutex_waiter waiter; |
| 147 | unsigned long flags; |
| 148 | |
| 149 | preempt_disable(); |
| 150 | mutex_acquire(&lock->dep_map, subclass, 0, ip); |
| 151 | |
| 152 | #ifdef CONFIG_MUTEX_SPIN_ON_OWNER |
| 153 | /* |
| 154 | * Optimistic spinning. |
| 155 | * |
| 156 | * We try to spin for acquisition when we find that there are no |
| 157 | * pending waiters and the lock owner is currently running on a |
| 158 | * (different) CPU. |
| 159 | * |
| 160 | * The rationale is that if the lock owner is running, it is likely to |
| 161 | * release the lock soon. |
| 162 | * |
| 163 | * Since this needs the lock owner, and this mutex implementation |
| 164 | * doesn't track the owner atomically in the lock field, we need to |
| 165 | * track it non-atomically. |
| 166 | * |
| 167 | * We can't do this for DEBUG_MUTEXES because that relies on wait_lock |
| 168 | * to serialize everything. |
| 169 | */ |
| 170 | |
| 171 | for (;;) { |
| 172 | struct thread_info *owner; |
| 173 | |
| 174 | /* |
| 175 | * If there's an owner, wait for it to either |
| 176 | * release the lock or go to sleep. |
| 177 | */ |
| 178 | owner = ACCESS_ONCE(lock->owner); |
| 179 | if (owner && !mutex_spin_on_owner(lock, owner)) |
| 180 | break; |
| 181 | |
| 182 | if (atomic_cmpxchg(&lock->count, 1, 0) == 1) { |
| 183 | lock_acquired(&lock->dep_map, ip); |
| 184 | mutex_set_owner(lock); |
| 185 | preempt_enable(); |
| 186 | return 0; |
| 187 | } |
| 188 | |
| 189 | /* |
| 190 | * When there's no owner, we might have preempted between the |
| 191 | * owner acquiring the lock and setting the owner field. If |
| 192 | * we're an RT task that will live-lock because we won't let |
| 193 | * the owner complete. |
| 194 | */ |
| 195 | if (!owner && (need_resched() || rt_task(task))) |
| 196 | break; |
| 197 | |
| 198 | /* |
| 199 | * The cpu_relax() call is a compiler barrier which forces |
| 200 | * everything in this loop to be re-loaded. We don't need |
| 201 | * memory barriers as we'll eventually observe the right |
| 202 | * values at the cost of a few extra spins. |
| 203 | */ |
| 204 | cpu_relax(); |
| 205 | } |
| 206 | #endif |
| 207 | spin_lock_mutex(&lock->wait_lock, flags); |
| 208 | |
| 209 | debug_mutex_lock_common(lock, &waiter); |
| 210 | debug_mutex_add_waiter(lock, &waiter, task_thread_info(task)); |
| 211 | |
| 212 | /* add waiting tasks to the end of the waitqueue (FIFO): */ |
| 213 | list_add_tail(&waiter.list, &lock->wait_list); |
| 214 | waiter.task = task; |
| 215 | |
| 216 | if (atomic_xchg(&lock->count, -1) == 1) |
| 217 | goto done; |
| 218 | |
| 219 | lock_contended(&lock->dep_map, ip); |
| 220 | |
| 221 | for (;;) { |
| 222 | /* |
| 223 | * Lets try to take the lock again - this is needed even if |
| 224 | * we get here for the first time (shortly after failing to |
| 225 | * acquire the lock), to make sure that we get a wakeup once |
| 226 | * it's unlocked. Later on, if we sleep, this is the |
| 227 | * operation that gives us the lock. We xchg it to -1, so |
| 228 | * that when we release the lock, we properly wake up the |
| 229 | * other waiters: |
| 230 | */ |
| 231 | if (atomic_xchg(&lock->count, -1) == 1) |
| 232 | break; |
| 233 | |
| 234 | /* |
| 235 | * got a signal? (This code gets eliminated in the |
| 236 | * TASK_UNINTERRUPTIBLE case.) |
| 237 | */ |
| 238 | if (unlikely(signal_pending_state(state, task))) { |
| 239 | mutex_remove_waiter(lock, &waiter, |
| 240 | task_thread_info(task)); |
| 241 | mutex_release(&lock->dep_map, 1, ip); |
| 242 | spin_unlock_mutex(&lock->wait_lock, flags); |
| 243 | |
| 244 | debug_mutex_free_waiter(&waiter); |
| 245 | preempt_enable(); |
| 246 | return -EINTR; |
| 247 | } |
| 248 | __set_task_state(task, state); |
| 249 | |
| 250 | /* didnt get the lock, go to sleep: */ |
| 251 | spin_unlock_mutex(&lock->wait_lock, flags); |
| 252 | preempt_enable_no_resched(); |
| 253 | schedule(); |
| 254 | preempt_disable(); |
| 255 | spin_lock_mutex(&lock->wait_lock, flags); |
| 256 | } |
| 257 | |
| 258 | done: |
| 259 | lock_acquired(&lock->dep_map, ip); |
| 260 | /* got the lock - rejoice! */ |
| 261 | mutex_remove_waiter(lock, &waiter, current_thread_info()); |
| 262 | mutex_set_owner(lock); |
| 263 | |
| 264 | /* set it to 0 if there are no waiters left: */ |
| 265 | if (likely(list_empty(&lock->wait_list))) |
| 266 | atomic_set(&lock->count, 0); |
| 267 | |
| 268 | spin_unlock_mutex(&lock->wait_lock, flags); |
| 269 | |
| 270 | debug_mutex_free_waiter(&waiter); |
| 271 | preempt_enable(); |
| 272 | |
| 273 | return 0; |
| 274 | } |
| 275 | |
| 276 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
| 277 | void __sched |
| 278 | mutex_lock_nested(struct mutex *lock, unsigned int subclass) |
| 279 | { |
| 280 | might_sleep(); |
| 281 | __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, subclass, _RET_IP_); |
| 282 | } |
| 283 | |
| 284 | EXPORT_SYMBOL_GPL(mutex_lock_nested); |
| 285 | |
| 286 | int __sched |
| 287 | mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass) |
| 288 | { |
| 289 | might_sleep(); |
| 290 | return __mutex_lock_common(lock, TASK_KILLABLE, subclass, _RET_IP_); |
| 291 | } |
| 292 | EXPORT_SYMBOL_GPL(mutex_lock_killable_nested); |
| 293 | |
| 294 | int __sched |
| 295 | mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass) |
| 296 | { |
| 297 | might_sleep(); |
| 298 | return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, |
| 299 | subclass, _RET_IP_); |
| 300 | } |
| 301 | |
| 302 | EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested); |
| 303 | #endif |
| 304 | |
| 305 | /* |
| 306 | * Release the lock, slowpath: |
| 307 | */ |
| 308 | static inline void |
| 309 | __mutex_unlock_common_slowpath(atomic_t *lock_count, int nested) |
| 310 | { |
| 311 | struct mutex *lock = container_of(lock_count, struct mutex, count); |
| 312 | unsigned long flags; |
| 313 | |
| 314 | spin_lock_mutex(&lock->wait_lock, flags); |
| 315 | mutex_release(&lock->dep_map, nested, _RET_IP_); |
| 316 | debug_mutex_unlock(lock); |
| 317 | |
| 318 | /* |
| 319 | * some architectures leave the lock unlocked in the fastpath failure |
| 320 | * case, others need to leave it locked. In the later case we have to |
| 321 | * unlock it here |
| 322 | */ |
| 323 | if (__mutex_slowpath_needs_to_unlock()) |
| 324 | atomic_set(&lock->count, 1); |
| 325 | |
| 326 | if (!list_empty(&lock->wait_list)) { |
| 327 | /* get the first entry from the wait-list: */ |
| 328 | struct mutex_waiter *waiter = |
| 329 | list_entry(lock->wait_list.next, |
| 330 | struct mutex_waiter, list); |
| 331 | |
| 332 | debug_mutex_wake_waiter(lock, waiter); |
| 333 | |
| 334 | wake_up_process(waiter->task); |
| 335 | } |
| 336 | |
| 337 | spin_unlock_mutex(&lock->wait_lock, flags); |
| 338 | } |
| 339 | |
| 340 | /* |
| 341 | * Release the lock, slowpath: |
| 342 | */ |
| 343 | static __used noinline void |
| 344 | __mutex_unlock_slowpath(atomic_t *lock_count) |
| 345 | { |
| 346 | __mutex_unlock_common_slowpath(lock_count, 1); |
| 347 | } |
| 348 | |
| 349 | #ifndef CONFIG_DEBUG_LOCK_ALLOC |
| 350 | /* |
| 351 | * Here come the less common (and hence less performance-critical) APIs: |
| 352 | * mutex_lock_interruptible() and mutex_trylock(). |
| 353 | */ |
| 354 | static noinline int __sched |
| 355 | __mutex_lock_killable_slowpath(atomic_t *lock_count); |
| 356 | |
| 357 | static noinline int __sched |
| 358 | __mutex_lock_interruptible_slowpath(atomic_t *lock_count); |
| 359 | |
| 360 | /*** |
| 361 | * mutex_lock_interruptible - acquire the mutex, interruptable |
| 362 | * @lock: the mutex to be acquired |
| 363 | * |
| 364 | * Lock the mutex like mutex_lock(), and return 0 if the mutex has |
| 365 | * been acquired or sleep until the mutex becomes available. If a |
| 366 | * signal arrives while waiting for the lock then this function |
| 367 | * returns -EINTR. |
| 368 | * |
| 369 | * This function is similar to (but not equivalent to) down_interruptible(). |
| 370 | */ |
| 371 | int __sched mutex_lock_interruptible(struct mutex *lock) |
| 372 | { |
| 373 | int ret; |
| 374 | |
| 375 | might_sleep(); |
| 376 | ret = __mutex_fastpath_lock_retval |
| 377 | (&lock->count, __mutex_lock_interruptible_slowpath); |
| 378 | if (!ret) |
| 379 | mutex_set_owner(lock); |
| 380 | |
| 381 | return ret; |
| 382 | } |
| 383 | |
| 384 | EXPORT_SYMBOL(mutex_lock_interruptible); |
| 385 | |
| 386 | int __sched mutex_lock_killable(struct mutex *lock) |
| 387 | { |
| 388 | int ret; |
| 389 | |
| 390 | might_sleep(); |
| 391 | ret = __mutex_fastpath_lock_retval |
| 392 | (&lock->count, __mutex_lock_killable_slowpath); |
| 393 | if (!ret) |
| 394 | mutex_set_owner(lock); |
| 395 | |
| 396 | return ret; |
| 397 | } |
| 398 | EXPORT_SYMBOL(mutex_lock_killable); |
| 399 | |
| 400 | static __used noinline void __sched |
| 401 | __mutex_lock_slowpath(atomic_t *lock_count) |
| 402 | { |
| 403 | struct mutex *lock = container_of(lock_count, struct mutex, count); |
| 404 | |
| 405 | __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0, _RET_IP_); |
| 406 | } |
| 407 | |
| 408 | static noinline int __sched |
| 409 | __mutex_lock_killable_slowpath(atomic_t *lock_count) |
| 410 | { |
| 411 | struct mutex *lock = container_of(lock_count, struct mutex, count); |
| 412 | |
| 413 | return __mutex_lock_common(lock, TASK_KILLABLE, 0, _RET_IP_); |
| 414 | } |
| 415 | |
| 416 | static noinline int __sched |
| 417 | __mutex_lock_interruptible_slowpath(atomic_t *lock_count) |
| 418 | { |
| 419 | struct mutex *lock = container_of(lock_count, struct mutex, count); |
| 420 | |
| 421 | return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, 0, _RET_IP_); |
| 422 | } |
| 423 | #endif |
| 424 | |
| 425 | /* |
| 426 | * Spinlock based trylock, we take the spinlock and check whether we |
| 427 | * can get the lock: |
| 428 | */ |
| 429 | static inline int __mutex_trylock_slowpath(atomic_t *lock_count) |
| 430 | { |
| 431 | struct mutex *lock = container_of(lock_count, struct mutex, count); |
| 432 | unsigned long flags; |
| 433 | int prev; |
| 434 | |
| 435 | spin_lock_mutex(&lock->wait_lock, flags); |
| 436 | |
| 437 | prev = atomic_xchg(&lock->count, -1); |
| 438 | if (likely(prev == 1)) { |
| 439 | mutex_set_owner(lock); |
| 440 | mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_); |
| 441 | } |
| 442 | |
| 443 | /* Set it back to 0 if there are no waiters: */ |
| 444 | if (likely(list_empty(&lock->wait_list))) |
| 445 | atomic_set(&lock->count, 0); |
| 446 | |
| 447 | spin_unlock_mutex(&lock->wait_lock, flags); |
| 448 | |
| 449 | return prev == 1; |
| 450 | } |
| 451 | |
| 452 | /*** |
| 453 | * mutex_trylock - try acquire the mutex, without waiting |
| 454 | * @lock: the mutex to be acquired |
| 455 | * |
| 456 | * Try to acquire the mutex atomically. Returns 1 if the mutex |
| 457 | * has been acquired successfully, and 0 on contention. |
| 458 | * |
| 459 | * NOTE: this function follows the spin_trylock() convention, so |
| 460 | * it is negated to the down_trylock() return values! Be careful |
| 461 | * about this when converting semaphore users to mutexes. |
| 462 | * |
| 463 | * This function must not be used in interrupt context. The |
| 464 | * mutex must be released by the same task that acquired it. |
| 465 | */ |
| 466 | int __sched mutex_trylock(struct mutex *lock) |
| 467 | { |
| 468 | int ret; |
| 469 | |
| 470 | ret = __mutex_fastpath_trylock(&lock->count, __mutex_trylock_slowpath); |
| 471 | if (ret) |
| 472 | mutex_set_owner(lock); |
| 473 | |
| 474 | return ret; |
| 475 | } |
| 476 | EXPORT_SYMBOL(mutex_trylock); |
| 477 | |
| 478 | /** |
| 479 | * atomic_dec_and_mutex_lock - return holding mutex if we dec to 0 |
| 480 | * @cnt: the atomic which we are to dec |
| 481 | * @lock: the mutex to return holding if we dec to 0 |
| 482 | * |
| 483 | * return true and hold lock if we dec to 0, return false otherwise |
| 484 | */ |
| 485 | int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock) |
| 486 | { |
| 487 | /* dec if we can't possibly hit 0 */ |
| 488 | if (atomic_add_unless(cnt, -1, 1)) |
| 489 | return 0; |
| 490 | /* we might hit 0, so take the lock */ |
| 491 | mutex_lock(lock); |
| 492 | if (!atomic_dec_and_test(cnt)) { |
| 493 | /* when we actually did the dec, we didn't hit 0 */ |
| 494 | mutex_unlock(lock); |
| 495 | return 0; |
| 496 | } |
| 497 | /* we hit 0, and we hold the lock */ |
| 498 | return 1; |
| 499 | } |
| 500 | EXPORT_SYMBOL(atomic_dec_and_mutex_lock); |