| 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 | * Also see Documentation/mutex-design.txt. |
| 14 | */ |
| 15 | #include <linux/mutex.h> |
| 16 | #include <linux/sched.h> |
| 17 | #include <linux/module.h> |
| 18 | #include <linux/spinlock.h> |
| 19 | #include <linux/interrupt.h> |
| 20 | #include <linux/debug_locks.h> |
| 21 | |
| 22 | /* |
| 23 | * In the DEBUG case we are using the "NULL fastpath" for mutexes, |
| 24 | * which forces all calls into the slowpath: |
| 25 | */ |
| 26 | #ifdef CONFIG_DEBUG_MUTEXES |
| 27 | # include "mutex-debug.h" |
| 28 | # include <asm-generic/mutex-null.h> |
| 29 | #else |
| 30 | # include "mutex.h" |
| 31 | # include <asm/mutex.h> |
| 32 | #endif |
| 33 | |
| 34 | /*** |
| 35 | * mutex_init - initialize the mutex |
| 36 | * @lock: the mutex to be initialized |
| 37 | * @key: the lock_class_key for the class; used by mutex lock debugging |
| 38 | * |
| 39 | * Initialize the mutex to unlocked state. |
| 40 | * |
| 41 | * It is not allowed to initialize an already locked mutex. |
| 42 | */ |
| 43 | void |
| 44 | __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key) |
| 45 | { |
| 46 | atomic_set(&lock->count, 1); |
| 47 | spin_lock_init(&lock->wait_lock); |
| 48 | INIT_LIST_HEAD(&lock->wait_list); |
| 49 | |
| 50 | debug_mutex_init(lock, name, key); |
| 51 | } |
| 52 | |
| 53 | EXPORT_SYMBOL(__mutex_init); |
| 54 | |
| 55 | #ifndef CONFIG_DEBUG_LOCK_ALLOC |
| 56 | /* |
| 57 | * We split the mutex lock/unlock logic into separate fastpath and |
| 58 | * slowpath functions, to reduce the register pressure on the fastpath. |
| 59 | * We also put the fastpath first in the kernel image, to make sure the |
| 60 | * branch is predicted by the CPU as default-untaken. |
| 61 | */ |
| 62 | static __used noinline void __sched |
| 63 | __mutex_lock_slowpath(atomic_t *lock_count); |
| 64 | |
| 65 | /*** |
| 66 | * mutex_lock - acquire the mutex |
| 67 | * @lock: the mutex to be acquired |
| 68 | * |
| 69 | * Lock the mutex exclusively for this task. If the mutex is not |
| 70 | * available right now, it will sleep until it can get it. |
| 71 | * |
| 72 | * The mutex must later on be released by the same task that |
| 73 | * acquired it. Recursive locking is not allowed. The task |
| 74 | * may not exit without first unlocking the mutex. Also, kernel |
| 75 | * memory where the mutex resides mutex must not be freed with |
| 76 | * the mutex still locked. The mutex must first be initialized |
| 77 | * (or statically defined) before it can be locked. memset()-ing |
| 78 | * the mutex to 0 is not allowed. |
| 79 | * |
| 80 | * ( The CONFIG_DEBUG_MUTEXES .config option turns on debugging |
| 81 | * checks that will enforce the restrictions and will also do |
| 82 | * deadlock debugging. ) |
| 83 | * |
| 84 | * This function is similar to (but not equivalent to) down(). |
| 85 | */ |
| 86 | void inline __sched mutex_lock(struct mutex *lock) |
| 87 | { |
| 88 | might_sleep(); |
| 89 | /* |
| 90 | * The locking fastpath is the 1->0 transition from |
| 91 | * 'unlocked' into 'locked' state. |
| 92 | */ |
| 93 | __mutex_fastpath_lock(&lock->count, __mutex_lock_slowpath); |
| 94 | } |
| 95 | |
| 96 | EXPORT_SYMBOL(mutex_lock); |
| 97 | #endif |
| 98 | |
| 99 | static __used noinline void __sched __mutex_unlock_slowpath(atomic_t *lock_count); |
| 100 | |
| 101 | /*** |
| 102 | * mutex_unlock - release the mutex |
| 103 | * @lock: the mutex to be released |
| 104 | * |
| 105 | * Unlock a mutex that has been locked by this task previously. |
| 106 | * |
| 107 | * This function must not be used in interrupt context. Unlocking |
| 108 | * of a not locked mutex is not allowed. |
| 109 | * |
| 110 | * This function is similar to (but not equivalent to) up(). |
| 111 | */ |
| 112 | void __sched mutex_unlock(struct mutex *lock) |
| 113 | { |
| 114 | /* |
| 115 | * The unlocking fastpath is the 0->1 transition from 'locked' |
| 116 | * into 'unlocked' state: |
| 117 | */ |
| 118 | __mutex_fastpath_unlock(&lock->count, __mutex_unlock_slowpath); |
| 119 | } |
| 120 | |
| 121 | EXPORT_SYMBOL(mutex_unlock); |
| 122 | |
| 123 | /* |
| 124 | * Lock a mutex (possibly interruptible), slowpath: |
| 125 | */ |
| 126 | static inline int __sched |
| 127 | __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, |
| 128 | unsigned long ip) |
| 129 | { |
| 130 | struct task_struct *task = current; |
| 131 | struct mutex_waiter waiter; |
| 132 | unsigned int old_val; |
| 133 | unsigned long flags; |
| 134 | |
| 135 | spin_lock_mutex(&lock->wait_lock, flags); |
| 136 | |
| 137 | debug_mutex_lock_common(lock, &waiter); |
| 138 | mutex_acquire(&lock->dep_map, subclass, 0, ip); |
| 139 | debug_mutex_add_waiter(lock, &waiter, task_thread_info(task)); |
| 140 | |
| 141 | /* add waiting tasks to the end of the waitqueue (FIFO): */ |
| 142 | list_add_tail(&waiter.list, &lock->wait_list); |
| 143 | waiter.task = task; |
| 144 | |
| 145 | old_val = atomic_xchg(&lock->count, -1); |
| 146 | if (old_val == 1) |
| 147 | goto done; |
| 148 | |
| 149 | lock_contended(&lock->dep_map, ip); |
| 150 | |
| 151 | for (;;) { |
| 152 | /* |
| 153 | * Lets try to take the lock again - this is needed even if |
| 154 | * we get here for the first time (shortly after failing to |
| 155 | * acquire the lock), to make sure that we get a wakeup once |
| 156 | * it's unlocked. Later on, if we sleep, this is the |
| 157 | * operation that gives us the lock. We xchg it to -1, so |
| 158 | * that when we release the lock, we properly wake up the |
| 159 | * other waiters: |
| 160 | */ |
| 161 | old_val = atomic_xchg(&lock->count, -1); |
| 162 | if (old_val == 1) |
| 163 | break; |
| 164 | |
| 165 | /* |
| 166 | * got a signal? (This code gets eliminated in the |
| 167 | * TASK_UNINTERRUPTIBLE case.) |
| 168 | */ |
| 169 | if (unlikely(signal_pending_state(state, task))) { |
| 170 | mutex_remove_waiter(lock, &waiter, |
| 171 | task_thread_info(task)); |
| 172 | mutex_release(&lock->dep_map, 1, ip); |
| 173 | spin_unlock_mutex(&lock->wait_lock, flags); |
| 174 | |
| 175 | debug_mutex_free_waiter(&waiter); |
| 176 | return -EINTR; |
| 177 | } |
| 178 | __set_task_state(task, state); |
| 179 | |
| 180 | /* didnt get the lock, go to sleep: */ |
| 181 | spin_unlock_mutex(&lock->wait_lock, flags); |
| 182 | schedule(); |
| 183 | spin_lock_mutex(&lock->wait_lock, flags); |
| 184 | } |
| 185 | |
| 186 | done: |
| 187 | lock_acquired(&lock->dep_map, ip); |
| 188 | /* got the lock - rejoice! */ |
| 189 | mutex_remove_waiter(lock, &waiter, task_thread_info(task)); |
| 190 | debug_mutex_set_owner(lock, task_thread_info(task)); |
| 191 | |
| 192 | /* set it to 0 if there are no waiters left: */ |
| 193 | if (likely(list_empty(&lock->wait_list))) |
| 194 | atomic_set(&lock->count, 0); |
| 195 | |
| 196 | spin_unlock_mutex(&lock->wait_lock, flags); |
| 197 | |
| 198 | debug_mutex_free_waiter(&waiter); |
| 199 | |
| 200 | return 0; |
| 201 | } |
| 202 | |
| 203 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
| 204 | void __sched |
| 205 | mutex_lock_nested(struct mutex *lock, unsigned int subclass) |
| 206 | { |
| 207 | might_sleep(); |
| 208 | __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, subclass, _RET_IP_); |
| 209 | } |
| 210 | |
| 211 | EXPORT_SYMBOL_GPL(mutex_lock_nested); |
| 212 | |
| 213 | int __sched |
| 214 | mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass) |
| 215 | { |
| 216 | might_sleep(); |
| 217 | return __mutex_lock_common(lock, TASK_KILLABLE, subclass, _RET_IP_); |
| 218 | } |
| 219 | EXPORT_SYMBOL_GPL(mutex_lock_killable_nested); |
| 220 | |
| 221 | int __sched |
| 222 | mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass) |
| 223 | { |
| 224 | might_sleep(); |
| 225 | return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, subclass, _RET_IP_); |
| 226 | } |
| 227 | |
| 228 | EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested); |
| 229 | #endif |
| 230 | |
| 231 | /* |
| 232 | * Release the lock, slowpath: |
| 233 | */ |
| 234 | static inline void |
| 235 | __mutex_unlock_common_slowpath(atomic_t *lock_count, int nested) |
| 236 | { |
| 237 | struct mutex *lock = container_of(lock_count, struct mutex, count); |
| 238 | unsigned long flags; |
| 239 | |
| 240 | spin_lock_mutex(&lock->wait_lock, flags); |
| 241 | mutex_release(&lock->dep_map, nested, _RET_IP_); |
| 242 | debug_mutex_unlock(lock); |
| 243 | |
| 244 | /* |
| 245 | * some architectures leave the lock unlocked in the fastpath failure |
| 246 | * case, others need to leave it locked. In the later case we have to |
| 247 | * unlock it here |
| 248 | */ |
| 249 | if (__mutex_slowpath_needs_to_unlock()) |
| 250 | atomic_set(&lock->count, 1); |
| 251 | |
| 252 | if (!list_empty(&lock->wait_list)) { |
| 253 | /* get the first entry from the wait-list: */ |
| 254 | struct mutex_waiter *waiter = |
| 255 | list_entry(lock->wait_list.next, |
| 256 | struct mutex_waiter, list); |
| 257 | |
| 258 | debug_mutex_wake_waiter(lock, waiter); |
| 259 | |
| 260 | wake_up_process(waiter->task); |
| 261 | } |
| 262 | |
| 263 | debug_mutex_clear_owner(lock); |
| 264 | |
| 265 | spin_unlock_mutex(&lock->wait_lock, flags); |
| 266 | } |
| 267 | |
| 268 | /* |
| 269 | * Release the lock, slowpath: |
| 270 | */ |
| 271 | static __used noinline void |
| 272 | __mutex_unlock_slowpath(atomic_t *lock_count) |
| 273 | { |
| 274 | __mutex_unlock_common_slowpath(lock_count, 1); |
| 275 | } |
| 276 | |
| 277 | #ifndef CONFIG_DEBUG_LOCK_ALLOC |
| 278 | /* |
| 279 | * Here come the less common (and hence less performance-critical) APIs: |
| 280 | * mutex_lock_interruptible() and mutex_trylock(). |
| 281 | */ |
| 282 | static noinline int __sched |
| 283 | __mutex_lock_killable_slowpath(atomic_t *lock_count); |
| 284 | |
| 285 | static noinline int __sched |
| 286 | __mutex_lock_interruptible_slowpath(atomic_t *lock_count); |
| 287 | |
| 288 | /*** |
| 289 | * mutex_lock_interruptible - acquire the mutex, interruptable |
| 290 | * @lock: the mutex to be acquired |
| 291 | * |
| 292 | * Lock the mutex like mutex_lock(), and return 0 if the mutex has |
| 293 | * been acquired or sleep until the mutex becomes available. If a |
| 294 | * signal arrives while waiting for the lock then this function |
| 295 | * returns -EINTR. |
| 296 | * |
| 297 | * This function is similar to (but not equivalent to) down_interruptible(). |
| 298 | */ |
| 299 | int __sched mutex_lock_interruptible(struct mutex *lock) |
| 300 | { |
| 301 | might_sleep(); |
| 302 | return __mutex_fastpath_lock_retval |
| 303 | (&lock->count, __mutex_lock_interruptible_slowpath); |
| 304 | } |
| 305 | |
| 306 | EXPORT_SYMBOL(mutex_lock_interruptible); |
| 307 | |
| 308 | int __sched mutex_lock_killable(struct mutex *lock) |
| 309 | { |
| 310 | might_sleep(); |
| 311 | return __mutex_fastpath_lock_retval |
| 312 | (&lock->count, __mutex_lock_killable_slowpath); |
| 313 | } |
| 314 | EXPORT_SYMBOL(mutex_lock_killable); |
| 315 | |
| 316 | static __used noinline void __sched |
| 317 | __mutex_lock_slowpath(atomic_t *lock_count) |
| 318 | { |
| 319 | struct mutex *lock = container_of(lock_count, struct mutex, count); |
| 320 | |
| 321 | __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0, _RET_IP_); |
| 322 | } |
| 323 | |
| 324 | static noinline int __sched |
| 325 | __mutex_lock_killable_slowpath(atomic_t *lock_count) |
| 326 | { |
| 327 | struct mutex *lock = container_of(lock_count, struct mutex, count); |
| 328 | |
| 329 | return __mutex_lock_common(lock, TASK_KILLABLE, 0, _RET_IP_); |
| 330 | } |
| 331 | |
| 332 | static noinline int __sched |
| 333 | __mutex_lock_interruptible_slowpath(atomic_t *lock_count) |
| 334 | { |
| 335 | struct mutex *lock = container_of(lock_count, struct mutex, count); |
| 336 | |
| 337 | return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, 0, _RET_IP_); |
| 338 | } |
| 339 | #endif |
| 340 | |
| 341 | /* |
| 342 | * Spinlock based trylock, we take the spinlock and check whether we |
| 343 | * can get the lock: |
| 344 | */ |
| 345 | static inline int __mutex_trylock_slowpath(atomic_t *lock_count) |
| 346 | { |
| 347 | struct mutex *lock = container_of(lock_count, struct mutex, count); |
| 348 | unsigned long flags; |
| 349 | int prev; |
| 350 | |
| 351 | spin_lock_mutex(&lock->wait_lock, flags); |
| 352 | |
| 353 | prev = atomic_xchg(&lock->count, -1); |
| 354 | if (likely(prev == 1)) { |
| 355 | debug_mutex_set_owner(lock, current_thread_info()); |
| 356 | mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_); |
| 357 | } |
| 358 | /* Set it back to 0 if there are no waiters: */ |
| 359 | if (likely(list_empty(&lock->wait_list))) |
| 360 | atomic_set(&lock->count, 0); |
| 361 | |
| 362 | spin_unlock_mutex(&lock->wait_lock, flags); |
| 363 | |
| 364 | return prev == 1; |
| 365 | } |
| 366 | |
| 367 | /*** |
| 368 | * mutex_trylock - try acquire the mutex, without waiting |
| 369 | * @lock: the mutex to be acquired |
| 370 | * |
| 371 | * Try to acquire the mutex atomically. Returns 1 if the mutex |
| 372 | * has been acquired successfully, and 0 on contention. |
| 373 | * |
| 374 | * NOTE: this function follows the spin_trylock() convention, so |
| 375 | * it is negated to the down_trylock() return values! Be careful |
| 376 | * about this when converting semaphore users to mutexes. |
| 377 | * |
| 378 | * This function must not be used in interrupt context. The |
| 379 | * mutex must be released by the same task that acquired it. |
| 380 | */ |
| 381 | int __sched mutex_trylock(struct mutex *lock) |
| 382 | { |
| 383 | return __mutex_fastpath_trylock(&lock->count, |
| 384 | __mutex_trylock_slowpath); |
| 385 | } |
| 386 | |
| 387 | EXPORT_SYMBOL(mutex_trylock); |