kernel/mutex.c

   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 void noinline __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 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);
 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 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 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);