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 fastcall 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 fastcall __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 void fastcall noinline __sched
  99 __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 fastcall __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(state == TASK_INTERRUPTIBLE &&
 170                                                 signal_pending(task))) {
 171                         mutex_remove_waiter(lock, &waiter, 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_interruptible_nested(struct mutex *lock, unsigned int subclass)
 215 {
 216         might_sleep();
 217         return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, subclass, _RET_IP_);
 218 }
 219
 220 EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested);
 221 #endif
 222
 223 /*
 224  * Release the lock, slowpath:
 225  */
 226 static fastcall inline void
 227 __mutex_unlock_common_slowpath(atomic_t *lock_count, int nested)
 228 {
 229         struct mutex *lock = container_of(lock_count, struct mutex, count);
 230         unsigned long flags;
 231
 232         spin_lock_mutex(&lock->wait_lock, flags);
 233         mutex_release(&lock->dep_map, nested, _RET_IP_);
 234         debug_mutex_unlock(lock);
 235
 236         /*
 237          * some architectures leave the lock unlocked in the fastpath failure
 238          * case, others need to leave it locked. In the later case we have to
 239          * unlock it here
 240          */
 241         if (__mutex_slowpath_needs_to_unlock())
 242                 atomic_set(&lock->count, 1);
 243
 244         if (!list_empty(&lock->wait_list)) {
 245                 /* get the first entry from the wait-list: */
 246                 struct mutex_waiter *waiter =
 247                                 list_entry(lock->wait_list.next,
 248                                            struct mutex_waiter, list);
 249
 250                 debug_mutex_wake_waiter(lock, waiter);
 251
 252                 wake_up_process(waiter->task);
 253         }
 254
 255         debug_mutex_clear_owner(lock);
 256
 257         spin_unlock_mutex(&lock->wait_lock, flags);
 258 }
 259
 260 /*
 261  * Release the lock, slowpath:
 262  */
 263 static fastcall noinline void
 264 __mutex_unlock_slowpath(atomic_t *lock_count)
 265 {
 266         __mutex_unlock_common_slowpath(lock_count, 1);
 267 }
 268
 269 #ifndef CONFIG_DEBUG_LOCK_ALLOC
 270 /*
 271  * Here come the less common (and hence less performance-critical) APIs:
 272  * mutex_lock_interruptible() and mutex_trylock().
 273  */
 274 static int fastcall noinline __sched
 275 __mutex_lock_interruptible_slowpath(atomic_t *lock_count);
 276
 277 /***
 278  * mutex_lock_interruptible - acquire the mutex, interruptable
 279  * @lock: the mutex to be acquired
 280  *
 281  * Lock the mutex like mutex_lock(), and return 0 if the mutex has
 282  * been acquired or sleep until the mutex becomes available. If a
 283  * signal arrives while waiting for the lock then this function
 284  * returns -EINTR.
 285  *
 286  * This function is similar to (but not equivalent to) down_interruptible().
 287  */
 288 int fastcall __sched mutex_lock_interruptible(struct mutex *lock)
 289 {
 290         might_sleep();
 291         return __mutex_fastpath_lock_retval
 292                         (&lock->count, __mutex_lock_interruptible_slowpath);
 293 }
 294
 295 EXPORT_SYMBOL(mutex_lock_interruptible);
 296
 297 static void fastcall noinline __sched
 298 __mutex_lock_slowpath(atomic_t *lock_count)
 299 {
 300         struct mutex *lock = container_of(lock_count, struct mutex, count);
 301
 302         __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0, _RET_IP_);
 303 }
 304
 305 static int fastcall noinline __sched
 306 __mutex_lock_interruptible_slowpath(atomic_t *lock_count)
 307 {
 308         struct mutex *lock = container_of(lock_count, struct mutex, count);
 309
 310         return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, 0, _RET_IP_);
 311 }
 312 #endif
 313
 314 /*
 315  * Spinlock based trylock, we take the spinlock and check whether we
 316  * can get the lock:
 317  */
 318 static inline int __mutex_trylock_slowpath(atomic_t *lock_count)
 319 {
 320         struct mutex *lock = container_of(lock_count, struct mutex, count);
 321         unsigned long flags;
 322         int prev;
 323
 324         spin_lock_mutex(&lock->wait_lock, flags);
 325
 326         prev = atomic_xchg(&lock->count, -1);
 327         if (likely(prev == 1)) {
 328                 debug_mutex_set_owner(lock, current_thread_info());
 329                 mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
 330         }
 331         /* Set it back to 0 if there are no waiters: */
 332         if (likely(list_empty(&lock->wait_list)))
 333                 atomic_set(&lock->count, 0);
 334
 335         spin_unlock_mutex(&lock->wait_lock, flags);
 336
 337         return prev == 1;
 338 }
 339
 340 /***
 341  * mutex_trylock - try acquire the mutex, without waiting
 342  * @lock: the mutex to be acquired
 343  *
 344  * Try to acquire the mutex atomically. Returns 1 if the mutex
 345  * has been acquired successfully, and 0 on contention.
 346  *
 347  * NOTE: this function follows the spin_trylock() convention, so
 348  * it is negated to the down_trylock() return values! Be careful
 349  * about this when converting semaphore users to mutexes.
 350  *
 351  * This function must not be used in interrupt context. The
 352  * mutex must be released by the same task that acquired it.
 353  */
 354 int fastcall __sched mutex_trylock(struct mutex *lock)
 355 {
 356         return __mutex_fastpath_trylock(&lock->count,
 357                                         __mutex_trylock_slowpath);
 358 }
 359
 360 EXPORT_SYMBOL(mutex_trylock);