include/linux/ww_mutex.h

   1 /*
   2  * Wound/Wait Mutexes: blocking mutual exclusion locks with deadlock avoidance
   3  *
   4  * Original mutex implementation started by Ingo Molnar:
   5  *
   6  *  Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
   7  *
   8  * Wound/wait implementation:
   9  *  Copyright (C) 2013 Canonical Ltd.
  10  *
  11  * This file contains the main data structure and API definitions.
  12  */
  13
  14 #ifndef __LINUX_WW_MUTEX_H
  15 #define __LINUX_WW_MUTEX_H
  16
  17 #include <linux/mutex.h>
  18
  19 struct ww_class {
  20         atomic_long_t stamp;
  21         struct lock_class_key acquire_key;
  22         struct lock_class_key mutex_key;
  23         const char *acquire_name;
  24         const char *mutex_name;
  25 };
  26
  27 struct ww_acquire_ctx {
  28         struct task_struct *task;
  29         unsigned long stamp;
  30         unsigned acquired;
  31 #ifdef CONFIG_DEBUG_MUTEXES
  32         unsigned done_acquire;
  33         struct ww_class *ww_class;
  34         struct ww_mutex *contending_lock;
  35 #endif
  36 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  37         struct lockdep_map dep_map;
  38 #endif
  39 #ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
  40         unsigned deadlock_inject_interval;
  41         unsigned deadlock_inject_countdown;
  42 #endif
  43 };
  44
  45 struct ww_mutex {
  46         struct mutex base;
  47         struct ww_acquire_ctx *ctx;
  48 #ifdef CONFIG_DEBUG_MUTEXES
  49         struct ww_class *ww_class;
  50 #endif
  51 };
  52
  53 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  54 # define __WW_CLASS_MUTEX_INITIALIZER(lockname, class) \
  55                 , .ww_class = class
  56 #else
  57 # define __WW_CLASS_MUTEX_INITIALIZER(lockname, class)
  58 #endif
  59
  60 #define __WW_CLASS_INITIALIZER(ww_class) \
  61                 { .stamp = ATOMIC_LONG_INIT(0) \
  62                 , .acquire_name = #ww_class "_acquire" \
  63                 , .mutex_name = #ww_class "_mutex" }
  64
  65 #define __WW_MUTEX_INITIALIZER(lockname, class) \
  66                 { .base =  __MUTEX_INITIALIZER(lockname.base) \
  67                 __WW_CLASS_MUTEX_INITIALIZER(lockname, class) }
  68
  69 #define DEFINE_WW_CLASS(classname) \
  70         struct ww_class classname = __WW_CLASS_INITIALIZER(classname)
  71
  72 #define DEFINE_WW_MUTEX(mutexname, ww_class) \
  73         struct ww_mutex mutexname = __WW_MUTEX_INITIALIZER(mutexname, ww_class)
  74
  75 /**
  76  * ww_mutex_init - initialize the w/w mutex
  77  * @lock: the mutex to be initialized
  78  * @ww_class: the w/w class the mutex should belong to
  79  *
  80  * Initialize the w/w mutex to unlocked state and associate it with the given
  81  * class.
  82  *
  83  * It is not allowed to initialize an already locked mutex.
  84  */
  85 static inline void ww_mutex_init(struct ww_mutex *lock,
  86                                  struct ww_class *ww_class)
  87 {
  88         __mutex_init(&lock->base, ww_class->mutex_name, &ww_class->mutex_key);
  89         lock->ctx = NULL;
  90 #ifdef CONFIG_DEBUG_MUTEXES
  91         lock->ww_class = ww_class;
  92 #endif
  93 }
  94
  95 /**
  96  * ww_acquire_init - initialize a w/w acquire context
  97  * @ctx: w/w acquire context to initialize
  98  * @ww_class: w/w class of the context
  99  *
 100  * Initializes an context to acquire multiple mutexes of the given w/w class.
 101  *
 102  * Context-based w/w mutex acquiring can be done in any order whatsoever within
 103  * a given lock class. Deadlocks will be detected and handled with the
 104  * wait/wound logic.
 105  *
 106  * Mixing of context-based w/w mutex acquiring and single w/w mutex locking can
 107  * result in undetected deadlocks and is so forbidden. Mixing different contexts
 108  * for the same w/w class when acquiring mutexes can also result in undetected
 109  * deadlocks, and is hence also forbidden. Both types of abuse will be caught by
 110  * enabling CONFIG_PROVE_LOCKING.
 111  *
 112  * Nesting of acquire contexts for _different_ w/w classes is possible, subject
 113  * to the usual locking rules between different lock classes.
 114  *
 115  * An acquire context must be released with ww_acquire_fini by the same task
 116  * before the memory is freed. It is recommended to allocate the context itself
 117  * on the stack.
 118  */
 119 static inline void ww_acquire_init(struct ww_acquire_ctx *ctx,
 120                                    struct ww_class *ww_class)
 121 {
 122         ctx->task = current;
 123         ctx->stamp = atomic_long_inc_return_relaxed(&ww_class->stamp);
 124         ctx->acquired = 0;
 125 #ifdef CONFIG_DEBUG_MUTEXES
 126         ctx->ww_class = ww_class;
 127         ctx->done_acquire = 0;
 128         ctx->contending_lock = NULL;
 129 #endif
 130 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 131         debug_check_no_locks_freed((void *)ctx, sizeof(*ctx));
 132         lockdep_init_map(&ctx->dep_map, ww_class->acquire_name,
 133                          &ww_class->acquire_key, 0);
 134         mutex_acquire(&ctx->dep_map, 0, 0, _RET_IP_);
 135 #endif
 136 #ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
 137         ctx->deadlock_inject_interval = 1;
 138         ctx->deadlock_inject_countdown = ctx->stamp & 0xf;
 139 #endif
 140 }
 141
 142 /**
 143  * ww_acquire_done - marks the end of the acquire phase
 144  * @ctx: the acquire context
 145  *
 146  * Marks the end of the acquire phase, any further w/w mutex lock calls using
 147  * this context are forbidden.
 148  *
 149  * Calling this function is optional, it is just useful to document w/w mutex
 150  * code and clearly designated the acquire phase from actually using the locked
 151  * data structures.
 152  */
 153 static inline void ww_acquire_done(struct ww_acquire_ctx *ctx)
 154 {
 155 #ifdef CONFIG_DEBUG_MUTEXES
 156         lockdep_assert_held(ctx);
 157
 158         DEBUG_LOCKS_WARN_ON(ctx->done_acquire);
 159         ctx->done_acquire = 1;
 160 #endif
 161 }
 162
 163 /**
 164  * ww_acquire_fini - releases a w/w acquire context
 165  * @ctx: the acquire context to free
 166  *
 167  * Releases a w/w acquire context. This must be called _after_ all acquired w/w
 168  * mutexes have been released with ww_mutex_unlock.
 169  */
 170 static inline void ww_acquire_fini(struct ww_acquire_ctx *ctx)
 171 {
 172 #ifdef CONFIG_DEBUG_MUTEXES
 173         mutex_release(&ctx->dep_map, 0, _THIS_IP_);
 174
 175         DEBUG_LOCKS_WARN_ON(ctx->acquired);
 176         if (!IS_ENABLED(CONFIG_PROVE_LOCKING))
 177                 /*
 178                  * lockdep will normally handle this,
 179                  * but fail without anyway
 180                  */
 181                 ctx->done_acquire = 1;
 182
 183         if (!IS_ENABLED(CONFIG_DEBUG_LOCK_ALLOC))
 184                 /* ensure ww_acquire_fini will still fail if called twice */
 185                 ctx->acquired = ~0U;
 186 #endif
 187 }
 188
 189 /**
 190  * ww_mutex_lock - acquire the w/w mutex
 191  * @lock: the mutex to be acquired
 192  * @ctx: w/w acquire context, or NULL to acquire only a single lock.
 193  *
 194  * Lock the w/w mutex exclusively for this task.
 195  *
 196  * Deadlocks within a given w/w class of locks are detected and handled with the
 197  * wait/wound algorithm. If the lock isn't immediately avaiable this function
 198  * will either sleep until it is (wait case). Or it selects the current context
 199  * for backing off by returning -EDEADLK (wound case). Trying to acquire the
 200  * same lock with the same context twice is also detected and signalled by
 201  * returning -EALREADY. Returns 0 if the mutex was successfully acquired.
 202  *
 203  * In the wound case the caller must release all currently held w/w mutexes for
 204  * the given context and then wait for this contending lock to be available by
 205  * calling ww_mutex_lock_slow. Alternatively callers can opt to not acquire this
 206  * lock and proceed with trying to acquire further w/w mutexes (e.g. when
 207  * scanning through lru lists trying to free resources).
 208  *
 209  * The mutex must later on be released by the same task that
 210  * acquired it. The task may not exit without first unlocking the mutex. Also,
 211  * kernel memory where the mutex resides must not be freed with the mutex still
 212  * locked. The mutex must first be initialized (or statically defined) before it
 213  * can be locked. memset()-ing the mutex to 0 is not allowed. The mutex must be
 214  * of the same w/w lock class as was used to initialize the acquire context.
 215  *
 216  * A mutex acquired with this function must be released with ww_mutex_unlock.
 217  */
 218 extern int /* __must_check */ ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx);
 219
 220 /**
 221  * ww_mutex_lock_interruptible - acquire the w/w mutex, interruptible
 222  * @lock: the mutex to be acquired
 223  * @ctx: w/w acquire context
 224  *
 225  * Lock the w/w mutex exclusively for this task.
 226  *
 227  * Deadlocks within a given w/w class of locks are detected and handled with the
 228  * wait/wound algorithm. If the lock isn't immediately avaiable this function
 229  * will either sleep until it is (wait case). Or it selects the current context
 230  * for backing off by returning -EDEADLK (wound case). Trying to acquire the
 231  * same lock with the same context twice is also detected and signalled by
 232  * returning -EALREADY. Returns 0 if the mutex was successfully acquired. If a
 233  * signal arrives while waiting for the lock then this function returns -EINTR.
 234  *
 235  * In the wound case the caller must release all currently held w/w mutexes for
 236  * the given context and then wait for this contending lock to be available by
 237  * calling ww_mutex_lock_slow_interruptible. Alternatively callers can opt to
 238  * not acquire this lock and proceed with trying to acquire further w/w mutexes
 239  * (e.g. when scanning through lru lists trying to free resources).
 240  *
 241  * The mutex must later on be released by the same task that
 242  * acquired it. The task may not exit without first unlocking the mutex. Also,
 243  * kernel memory where the mutex resides must not be freed with the mutex still
 244  * locked. The mutex must first be initialized (or statically defined) before it
 245  * can be locked. memset()-ing the mutex to 0 is not allowed. The mutex must be
 246  * of the same w/w lock class as was used to initialize the acquire context.
 247  *
 248  * A mutex acquired with this function must be released with ww_mutex_unlock.
 249  */
 250 extern int __must_check ww_mutex_lock_interruptible(struct ww_mutex *lock,
 251                                                     struct ww_acquire_ctx *ctx);
 252
 253 /**
 254  * ww_mutex_lock_slow - slowpath acquiring of the w/w mutex
 255  * @lock: the mutex to be acquired
 256  * @ctx: w/w acquire context
 257  *
 258  * Acquires a w/w mutex with the given context after a wound case. This function
 259  * will sleep until the lock becomes available.
 260  *
 261  * The caller must have released all w/w mutexes already acquired with the
 262  * context and then call this function on the contended lock.
 263  *
 264  * Afterwards the caller may continue to (re)acquire the other w/w mutexes it
 265  * needs with ww_mutex_lock. Note that the -EALREADY return code from
 266  * ww_mutex_lock can be used to avoid locking this contended mutex twice.
 267  *
 268  * It is forbidden to call this function with any other w/w mutexes associated
 269  * with the context held. It is forbidden to call this on anything else than the
 270  * contending mutex.
 271  *
 272  * Note that the slowpath lock acquiring can also be done by calling
 273  * ww_mutex_lock directly. This function here is simply to help w/w mutex
 274  * locking code readability by clearly denoting the slowpath.
 275  */
 276 static inline void
 277 ww_mutex_lock_slow(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 278 {
 279         int ret;
 280 #ifdef CONFIG_DEBUG_MUTEXES
 281         DEBUG_LOCKS_WARN_ON(!ctx->contending_lock);
 282 #endif
 283         ret = ww_mutex_lock(lock, ctx);
 284         (void)ret;
 285 }
 286
 287 /**
 288  * ww_mutex_lock_slow_interruptible - slowpath acquiring of the w/w mutex, interruptible
 289  * @lock: the mutex to be acquired
 290  * @ctx: w/w acquire context
 291  *
 292  * Acquires a w/w mutex with the given context after a wound case. This function
 293  * will sleep until the lock becomes available and returns 0 when the lock has
 294  * been acquired. If a signal arrives while waiting for the lock then this
 295  * function returns -EINTR.
 296  *
 297  * The caller must have released all w/w mutexes already acquired with the
 298  * context and then call this function on the contended lock.
 299  *
 300  * Afterwards the caller may continue to (re)acquire the other w/w mutexes it
 301  * needs with ww_mutex_lock. Note that the -EALREADY return code from
 302  * ww_mutex_lock can be used to avoid locking this contended mutex twice.
 303  *
 304  * It is forbidden to call this function with any other w/w mutexes associated
 305  * with the given context held. It is forbidden to call this on anything else
 306  * than the contending mutex.
 307  *
 308  * Note that the slowpath lock acquiring can also be done by calling
 309  * ww_mutex_lock_interruptible directly. This function here is simply to help
 310  * w/w mutex locking code readability by clearly denoting the slowpath.
 311  */
 312 static inline int __must_check
 313 ww_mutex_lock_slow_interruptible(struct ww_mutex *lock,
 314                                  struct ww_acquire_ctx *ctx)
 315 {
 316 #ifdef CONFIG_DEBUG_MUTEXES
 317         DEBUG_LOCKS_WARN_ON(!ctx->contending_lock);
 318 #endif
 319         return ww_mutex_lock_interruptible(lock, ctx);
 320 }
 321
 322 extern void ww_mutex_unlock(struct ww_mutex *lock);
 323
 324 /**
 325  * ww_mutex_trylock - tries to acquire the w/w mutex without acquire context
 326  * @lock: mutex to lock
 327  *
 328  * Trylocks a mutex without acquire context, so no deadlock detection is
 329  * possible. Returns 1 if the mutex has been acquired successfully, 0 otherwise.
 330  */
 331 static inline int __must_check ww_mutex_trylock(struct ww_mutex *lock)
 332 {
 333         return mutex_trylock(&lock->base);
 334 }
 335
 336 /***
 337  * ww_mutex_destroy - mark a w/w mutex unusable
 338  * @lock: the mutex to be destroyed
 339  *
 340  * This function marks the mutex uninitialized, and any subsequent
 341  * use of the mutex is forbidden. The mutex must not be locked when
 342  * this function is called.
 343  */
 344 static inline void ww_mutex_destroy(struct ww_mutex *lock)
 345 {
 346         mutex_destroy(&lock->base);
 347 }
 348
 349 /**
 350  * ww_mutex_is_locked - is the w/w mutex locked
 351  * @lock: the mutex to be queried
 352  *
 353  * Returns 1 if the mutex is locked, 0 if unlocked.
 354  */
 355 static inline bool ww_mutex_is_locked(struct ww_mutex *lock)
 356 {
 357         return mutex_is_locked(&lock->base);
 358 }
 359
 360 #endif