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  *
  38  * Initialize the mutex to unlocked state.
  39  *
  40  * It is not allowed to initialize an already locked mutex.
  41  */
  42 void
  43 __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
  44 {
  45         atomic_set(&lock->count, 1);
  46         spin_lock_init(&lock->wait_lock);
  47         INIT_LIST_HEAD(&lock->wait_list);
  48
  49         debug_mutex_init(lock, name, key);
  50 }
  51
  52 EXPORT_SYMBOL(__mutex_init);
  53
  54 #ifndef CONFIG_DEBUG_LOCK_ALLOC
  55 /*
  56  * We split the mutex lock/unlock logic into separate fastpath and
  57  * slowpath functions, to reduce the register pressure on the fastpath.
  58  * We also put the fastpath first in the kernel image, to make sure the
  59  * branch is predicted by the CPU as default-untaken.
  60  */
  61 static void noinline __sched
  62 __mutex_lock_slowpath(atomic_t *lock_count);
  63
  64 /***
  65  * mutex_lock - acquire the mutex
  66  * @lock: the mutex to be acquired
  67  *
  68  * Lock the mutex exclusively for this task. If the mutex is not
  69  * available right now, it will sleep until it can get it.
  70  *
  71  * The mutex must later on be released by the same task that
  72  * acquired it. Recursive locking is not allowed. The task
  73  * may not exit without first unlocking the mutex. Also, kernel
  74  * memory where the mutex resides mutex must not be freed with
  75  * the mutex still locked. The mutex must first be initialized
  76  * (or statically defined) before it can be locked. memset()-ing
  77  * the mutex to 0 is not allowed.
  78  *
  79  * ( The CONFIG_DEBUG_MUTEXES .config option turns on debugging
  80  *   checks that will enforce the restrictions and will also do
  81  *   deadlock debugging. )
  82  *
  83  * This function is similar to (but not equivalent to) down().
  84  */
  85 void inline __sched mutex_lock(struct mutex *lock)
  86 {
  87         might_sleep();
  88         /*
  89          * The locking fastpath is the 1->0 transition from
  90          * 'unlocked' into 'locked' state.
  91          */
  92         __mutex_fastpath_lock(&lock->count, __mutex_lock_slowpath);
  93 }
  94
  95 EXPORT_SYMBOL(mutex_lock);
  96 #endif
  97
  98 static noinline void __sched __mutex_unlock_slowpath(atomic_t *lock_count);
  99
 100 /***
 101  * mutex_unlock - release the mutex
 102  * @lock: the mutex to be released
 103  *
 104  * Unlock a mutex that has been locked by this task previously.
 105  *
 106  * This function must not be used in interrupt context. Unlocking
 107  * of a not locked mutex is not allowed.
 108  *
 109  * This function is similar to (but not equivalent to) up().
 110  */
 111 void __sched mutex_unlock(struct mutex *lock)
 112 {
 113         /*
 114          * The unlocking fastpath is the 0->1 transition from 'locked'
 115          * into 'unlocked' state:
 116          */
 117         __mutex_fastpath_unlock(&lock->count, __mutex_unlock_slowpath);
 118 }
 119
 120 EXPORT_SYMBOL(mutex_unlock);
 121
 122 /*
 123  * Lock a mutex (possibly interruptible), slowpath:
 124  */
 125 static inline int __sched
 126 __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
 127                 unsigned long ip)
 128 {
 129         struct task_struct *task = current;
 130         struct mutex_waiter waiter;
 131         unsigned int old_val;
 132         unsigned long flags;
 133
 134         spin_lock_mutex(&lock->wait_lock, flags);
 135
 136         debug_mutex_lock_common(lock, &waiter);
 137         mutex_acquire(&lock->dep_map, subclass, 0, ip);
 138         debug_mutex_add_waiter(lock, &waiter, task_thread_info(task));
 139
 140         /* add waiting tasks to the end of the waitqueue (FIFO): */
 141         list_add_tail(&waiter.list, &lock->wait_list);
 142         waiter.task = task;
 143
 144         old_val = atomic_xchg(&lock->count, -1);
 145         if (old_val == 1)
 146                 goto done;
 147
 148         lock_contended(&lock->dep_map, ip);
 149
 150         for (;;) {
 151                 /*
 152                  * Lets try to take the lock again - this is needed even if
 153                  * we get here for the first time (shortly after failing to
 154                  * acquire the lock), to make sure that we get a wakeup once
 155                  * it's unlocked. Later on, if we sleep, this is the
 156                  * operation that gives us the lock. We xchg it to -1, so
 157                  * that when we release the lock, we properly wake up the
 158                  * other waiters:
 159                  */
 160                 old_val = atomic_xchg(&lock->count, -1);
 161                 if (old_val == 1)
 162                         break;
 163
 164                 /*
 165                  * got a signal? (This code gets eliminated in the
 166                  * TASK_UNINTERRUPTIBLE case.)
 167                  */
 168                 if (unlikely((state == TASK_INTERRUPTIBLE &&
 169                                         signal_pending(task)) ||
 170                               (state == TASK_KILLABLE &&
 171                                         fatal_signal_pending(task)))) {
 172                         mutex_remove_waiter(lock, &waiter,
 173                                             task_thread_info(task));
 174                         mutex_release(&lock->dep_map, 1, ip);
 175                         spin_unlock_mutex(&lock->wait_lock, flags);
 176
 177                         debug_mutex_free_waiter(&waiter);
 178                         return -EINTR;
 179                 }
 180                 __set_task_state(task, state);
 181
 182                 /* didnt get the lock, go to sleep: */
 183                 spin_unlock_mutex(&lock->wait_lock, flags);
 184                 schedule();
 185                 spin_lock_mutex(&lock->wait_lock, flags);
 186         }
 187
 188 done:
 189         lock_acquired(&lock->dep_map);
 190         /* got the lock - rejoice! */
 191         mutex_remove_waiter(lock, &waiter, task_thread_info(task));
 192         debug_mutex_set_owner(lock, task_thread_info(task));
 193
 194         /* set it to 0 if there are no waiters left: */
 195         if (likely(list_empty(&lock->wait_list)))
 196                 atomic_set(&lock->count, 0);
 197
 198         spin_unlock_mutex(&lock->wait_lock, flags);
 199
 200         debug_mutex_free_waiter(&waiter);
 201
 202         return 0;
 203 }
 204
 205 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 206 void __sched
 207 mutex_lock_nested(struct mutex *lock, unsigned int subclass)
 208 {
 209         might_sleep();
 210         __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, subclass, _RET_IP_);
 211 }
 212
 213 EXPORT_SYMBOL_GPL(mutex_lock_nested);
 214
 215 int __sched
 216 mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass)
 217 {
 218         might_sleep();
 219         return __mutex_lock_common(lock, TASK_KILLABLE, subclass, _RET_IP_);
 220 }
 221 EXPORT_SYMBOL_GPL(mutex_lock_killable_nested);
 222
 223 int __sched
 224 mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass)
 225 {
 226         might_sleep();
 227         return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, subclass, _RET_IP_);
 228 }
 229
 230 EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested);
 231 #endif
 232
 233 /*
 234  * Release the lock, slowpath:
 235  */
 236 static inline void
 237 __mutex_unlock_common_slowpath(atomic_t *lock_count, int nested)
 238 {
 239         struct mutex *lock = container_of(lock_count, struct mutex, count);
 240         unsigned long flags;
 241
 242         spin_lock_mutex(&lock->wait_lock, flags);
 243         mutex_release(&lock->dep_map, nested, _RET_IP_);
 244         debug_mutex_unlock(lock);
 245
 246         /*
 247          * some architectures leave the lock unlocked in the fastpath failure
 248          * case, others need to leave it locked. In the later case we have to
 249          * unlock it here
 250          */
 251         if (__mutex_slowpath_needs_to_unlock())
 252                 atomic_set(&lock->count, 1);
 253
 254         if (!list_empty(&lock->wait_list)) {
 255                 /* get the first entry from the wait-list: */
 256                 struct mutex_waiter *waiter =
 257                                 list_entry(lock->wait_list.next,
 258                                            struct mutex_waiter, list);
 259
 260                 debug_mutex_wake_waiter(lock, waiter);
 261
 262                 wake_up_process(waiter->task);
 263         }
 264
 265         debug_mutex_clear_owner(lock);
 266
 267         spin_unlock_mutex(&lock->wait_lock, flags);
 268 }
 269
 270 /*
 271  * Release the lock, slowpath:
 272  */
 273 static noinline void
 274 __mutex_unlock_slowpath(atomic_t *lock_count)
 275 {
 276         __mutex_unlock_common_slowpath(lock_count, 1);
 277 }
 278
 279 #ifndef CONFIG_DEBUG_LOCK_ALLOC
 280 /*
 281  * Here come the less common (and hence less performance-critical) APIs:
 282  * mutex_lock_interruptible() and mutex_trylock().
 283  */
 284 static noinline int __sched
 285 __mutex_lock_killable_slowpath(atomic_t *lock_count);
 286
 287 static noinline int __sched
 288 __mutex_lock_interruptible_slowpath(atomic_t *lock_count);
 289
 290 /***
 291  * mutex_lock_interruptible - acquire the mutex, interruptable
 292  * @lock: the mutex to be acquired
 293  *
 294  * Lock the mutex like mutex_lock(), and return 0 if the mutex has
 295  * been acquired or sleep until the mutex becomes available. If a
 296  * signal arrives while waiting for the lock then this function
 297  * returns -EINTR.
 298  *
 299  * This function is similar to (but not equivalent to) down_interruptible().
 300  */
 301 int __sched mutex_lock_interruptible(struct mutex *lock)
 302 {
 303         might_sleep();
 304         return __mutex_fastpath_lock_retval
 305                         (&lock->count, __mutex_lock_interruptible_slowpath);
 306 }
 307
 308 EXPORT_SYMBOL(mutex_lock_interruptible);
 309
 310 int __sched mutex_lock_killable(struct mutex *lock)
 311 {
 312         might_sleep();
 313         return __mutex_fastpath_lock_retval
 314                         (&lock->count, __mutex_lock_killable_slowpath);
 315 }
 316 EXPORT_SYMBOL(mutex_lock_killable);
 317
 318 static noinline void __sched
 319 __mutex_lock_slowpath(atomic_t *lock_count)
 320 {
 321         struct mutex *lock = container_of(lock_count, struct mutex, count);
 322
 323         __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0, _RET_IP_);
 324 }
 325
 326 static noinline int __sched
 327 __mutex_lock_killable_slowpath(atomic_t *lock_count)
 328 {
 329         struct mutex *lock = container_of(lock_count, struct mutex, count);
 330
 331         return __mutex_lock_common(lock, TASK_KILLABLE, 0, _RET_IP_);
 332 }
 333
 334 static noinline int __sched
 335 __mutex_lock_interruptible_slowpath(atomic_t *lock_count)
 336 {
 337         struct mutex *lock = container_of(lock_count, struct mutex, count);
 338
 339         return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, 0, _RET_IP_);
 340 }
 341 #endif
 342
 343 /*
 344  * Spinlock based trylock, we take the spinlock and check whether we
 345  * can get the lock:
 346  */
 347 static inline int __mutex_trylock_slowpath(atomic_t *lock_count)
 348 {
 349         struct mutex *lock = container_of(lock_count, struct mutex, count);
 350         unsigned long flags;
 351         int prev;
 352
 353         spin_lock_mutex(&lock->wait_lock, flags);
 354
 355         prev = atomic_xchg(&lock->count, -1);
 356         if (likely(prev == 1)) {
 357                 debug_mutex_set_owner(lock, current_thread_info());
 358                 mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
 359         }
 360         /* Set it back to 0 if there are no waiters: */
 361         if (likely(list_empty(&lock->wait_list)))
 362                 atomic_set(&lock->count, 0);
 363
 364         spin_unlock_mutex(&lock->wait_lock, flags);
 365
 366         return prev == 1;
 367 }
 368
 369 /***
 370  * mutex_trylock - try acquire the mutex, without waiting
 371  * @lock: the mutex to be acquired
 372  *
 373  * Try to acquire the mutex atomically. Returns 1 if the mutex
 374  * has been acquired successfully, and 0 on contention.
 375  *
 376  * NOTE: this function follows the spin_trylock() convention, so
 377  * it is negated to the down_trylock() return values! Be careful
 378  * about this when converting semaphore users to mutexes.
 379  *
 380  * This function must not be used in interrupt context. The
 381  * mutex must be released by the same task that acquired it.
 382  */
 383 int __sched mutex_trylock(struct mutex *lock)
 384 {
 385         return __mutex_fastpath_trylock(&lock->count,
 386                                         __mutex_trylock_slowpath);
 387 }
 388
 389 EXPORT_SYMBOL(mutex_trylock);