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(signal_pending_state(state, task))) {
 169                         mutex_remove_waiter(lock, &waiter,
 170                                             task_thread_info(task));
 171                         mutex_release(&lock->dep_map, 1, ip);
 172                         spin_unlock_mutex(&lock->wait_lock, flags);
 173
 174                         debug_mutex_free_waiter(&waiter);
 175                         return -EINTR;
 176                 }
 177                 __set_task_state(task, state);
 178
 179                 /* didnt get the lock, go to sleep: */
 180                 spin_unlock_mutex(&lock->wait_lock, flags);
 181                 schedule();
 182                 spin_lock_mutex(&lock->wait_lock, flags);
 183         }
 184
 185 done:
 186         lock_acquired(&lock->dep_map);
 187         /* got the lock - rejoice! */
 188         mutex_remove_waiter(lock, &waiter, task_thread_info(task));
 189         debug_mutex_set_owner(lock, task_thread_info(task));
 190
 191         /* set it to 0 if there are no waiters left: */
 192         if (likely(list_empty(&lock->wait_list)))
 193                 atomic_set(&lock->count, 0);
 194
 195         spin_unlock_mutex(&lock->wait_lock, flags);
 196
 197         debug_mutex_free_waiter(&waiter);
 198
 199         return 0;
 200 }
 201
 202 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 203 void __sched
 204 mutex_lock_nested(struct mutex *lock, unsigned int subclass)
 205 {
 206         might_sleep();
 207         __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, subclass, _RET_IP_);
 208 }
 209
 210 EXPORT_SYMBOL_GPL(mutex_lock_nested);
 211
 212 int __sched
 213 mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass)
 214 {
 215         might_sleep();
 216         return __mutex_lock_common(lock, TASK_KILLABLE, subclass, _RET_IP_);
 217 }
 218 EXPORT_SYMBOL_GPL(mutex_lock_killable_nested);
 219
 220 int __sched
 221 mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass)
 222 {
 223         might_sleep();
 224         return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, subclass, _RET_IP_);
 225 }
 226
 227 EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested);
 228 #endif
 229
 230 /*
 231  * Release the lock, slowpath:
 232  */
 233 static inline void
 234 __mutex_unlock_common_slowpath(atomic_t *lock_count, int nested)
 235 {
 236         struct mutex *lock = container_of(lock_count, struct mutex, count);
 237         unsigned long flags;
 238
 239         spin_lock_mutex(&lock->wait_lock, flags);
 240         mutex_release(&lock->dep_map, nested, _RET_IP_);
 241         debug_mutex_unlock(lock);
 242
 243         /*
 244          * some architectures leave the lock unlocked in the fastpath failure
 245          * case, others need to leave it locked. In the later case we have to
 246          * unlock it here
 247          */
 248         if (__mutex_slowpath_needs_to_unlock())
 249                 atomic_set(&lock->count, 1);
 250
 251         if (!list_empty(&lock->wait_list)) {
 252                 /* get the first entry from the wait-list: */
 253                 struct mutex_waiter *waiter =
 254                                 list_entry(lock->wait_list.next,
 255                                            struct mutex_waiter, list);
 256
 257                 debug_mutex_wake_waiter(lock, waiter);
 258
 259                 wake_up_process(waiter->task);
 260         }
 261
 262         debug_mutex_clear_owner(lock);
 263
 264         spin_unlock_mutex(&lock->wait_lock, flags);
 265 }
 266
 267 /*
 268  * Release the lock, slowpath:
 269  */
 270 static noinline void
 271 __mutex_unlock_slowpath(atomic_t *lock_count)
 272 {
 273         __mutex_unlock_common_slowpath(lock_count, 1);
 274 }
 275
 276 #ifndef CONFIG_DEBUG_LOCK_ALLOC
 277 /*
 278  * Here come the less common (and hence less performance-critical) APIs:
 279  * mutex_lock_interruptible() and mutex_trylock().
 280  */
 281 static noinline int __sched
 282 __mutex_lock_killable_slowpath(atomic_t *lock_count);
 283
 284 static noinline int __sched
 285 __mutex_lock_interruptible_slowpath(atomic_t *lock_count);
 286
 287 /***
 288  * mutex_lock_interruptible - acquire the mutex, interruptable
 289  * @lock: the mutex to be acquired
 290  *
 291  * Lock the mutex like mutex_lock(), and return 0 if the mutex has
 292  * been acquired or sleep until the mutex becomes available. If a
 293  * signal arrives while waiting for the lock then this function
 294  * returns -EINTR.
 295  *
 296  * This function is similar to (but not equivalent to) down_interruptible().
 297  */
 298 int __sched mutex_lock_interruptible(struct mutex *lock)
 299 {
 300         might_sleep();
 301         return __mutex_fastpath_lock_retval
 302                         (&lock->count, __mutex_lock_interruptible_slowpath);
 303 }
 304
 305 EXPORT_SYMBOL(mutex_lock_interruptible);
 306
 307 int __sched mutex_lock_killable(struct mutex *lock)
 308 {
 309         might_sleep();
 310         return __mutex_fastpath_lock_retval
 311                         (&lock->count, __mutex_lock_killable_slowpath);
 312 }
 313 EXPORT_SYMBOL(mutex_lock_killable);
 314
 315 static noinline void __sched
 316 __mutex_lock_slowpath(atomic_t *lock_count)
 317 {
 318         struct mutex *lock = container_of(lock_count, struct mutex, count);
 319
 320         __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0, _RET_IP_);
 321 }
 322
 323 static noinline int __sched
 324 __mutex_lock_killable_slowpath(atomic_t *lock_count)
 325 {
 326         struct mutex *lock = container_of(lock_count, struct mutex, count);
 327
 328         return __mutex_lock_common(lock, TASK_KILLABLE, 0, _RET_IP_);
 329 }
 330
 331 static noinline int __sched
 332 __mutex_lock_interruptible_slowpath(atomic_t *lock_count)
 333 {
 334         struct mutex *lock = container_of(lock_count, struct mutex, count);
 335
 336         return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, 0, _RET_IP_);
 337 }
 338 #endif
 339
 340 /*
 341  * Spinlock based trylock, we take the spinlock and check whether we
 342  * can get the lock:
 343  */
 344 static inline int __mutex_trylock_slowpath(atomic_t *lock_count)
 345 {
 346         struct mutex *lock = container_of(lock_count, struct mutex, count);
 347         unsigned long flags;
 348         int prev;
 349
 350         spin_lock_mutex(&lock->wait_lock, flags);
 351
 352         prev = atomic_xchg(&lock->count, -1);
 353         if (likely(prev == 1)) {
 354                 debug_mutex_set_owner(lock, current_thread_info());
 355                 mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
 356         }
 357         /* Set it back to 0 if there are no waiters: */
 358         if (likely(list_empty(&lock->wait_list)))
 359                 atomic_set(&lock->count, 0);
 360
 361         spin_unlock_mutex(&lock->wait_lock, flags);
 362
 363         return prev == 1;
 364 }
 365
 366 /***
 367  * mutex_trylock - try acquire the mutex, without waiting
 368  * @lock: the mutex to be acquired
 369  *
 370  * Try to acquire the mutex atomically. Returns 1 if the mutex
 371  * has been acquired successfully, and 0 on contention.
 372  *
 373  * NOTE: this function follows the spin_trylock() convention, so
 374  * it is negated to the down_trylock() return values! Be careful
 375  * about this when converting semaphore users to mutexes.
 376  *
 377  * This function must not be used in interrupt context. The
 378  * mutex must be released by the same task that acquired it.
 379  */
 380 int __sched mutex_trylock(struct mutex *lock)
 381 {
 382         return __mutex_fastpath_trylock(&lock->count,
 383                                         __mutex_trylock_slowpath);
 384 }
 385
 386 EXPORT_SYMBOL(mutex_trylock);