include/linux/ww_mutex.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 /*
   3  * Wound/Wait Mutexes: blocking mutual exclusion locks with deadlock avoidance
   4  *
   5  * Original mutex implementation started by Ingo Molnar:
   6  *
   7  *  Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
   8  *
   9  * Wound/wait implementation:
  10  *  Copyright (C) 2013 Canonical Ltd.
  11  *
  12  * This file contains the main data structure and API definitions.
  13  */
  14
  15 #ifndef __LINUX_WW_MUTEX_H
  16 #define __LINUX_WW_MUTEX_H
  17
  18 #include <linux/mutex.h>
  19
  20 struct ww_class {
  21         atomic_long_t stamp;
  22         struct lock_class_key acquire_key;
  23         struct lock_class_key mutex_key;
  24         const char *acquire_name;
  25         const char *mutex_name;
  26 };
  27
  28 struct ww_acquire_ctx {
  29         struct task_struct *task;
  30         unsigned long stamp;
  31         unsigned acquired;
  32 #ifdef CONFIG_DEBUG_MUTEXES
  33         unsigned done_acquire;
  34         struct ww_class *ww_class;
  35         struct ww_mutex *contending_lock;
  36 #endif
  37 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  38         struct lockdep_map dep_map;
  39 #endif
  40 #ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
  41         unsigned deadlock_inject_interval;
  42         unsigned deadlock_inject_countdown;
  43 #endif
  44 };
  45
  46 struct ww_mutex {
  47         struct mutex base;
  48         struct ww_acquire_ctx *ctx;
  49 #ifdef CONFIG_DEBUG_MUTEXES
  50         struct ww_class *ww_class;
  51 #endif
  52 };
  53
  54 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  55 # define __WW_CLASS_MUTEX_INITIALIZER(lockname, class) \
  56                 , .ww_class = class
  57 #else
  58 # define __WW_CLASS_MUTEX_INITIALIZER(lockname, class)
  59 #endif
  60
  61 #define __WW_CLASS_INITIALIZER(ww_class) \
  62                 { .stamp = ATOMIC_LONG_INIT(0) \
  63                 , .acquire_name = #ww_class "_acquire" \
  64                 , .mutex_name = #ww_class "_mutex" }
  65
  66 #define __WW_MUTEX_INITIALIZER(lockname, class) \
  67                 { .base =  __MUTEX_INITIALIZER(lockname.base) \
  68                 __WW_CLASS_MUTEX_INITIALIZER(lockname, class) }
  69
  70 #define DEFINE_WW_CLASS(classname) \
  71         struct ww_class classname = __WW_CLASS_INITIALIZER(classname)
  72
  73 #define DEFINE_WW_MUTEX(mutexname, ww_class) \
  74         struct ww_mutex mutexname = __WW_MUTEX_INITIALIZER(mutexname, ww_class)
  75
  76 /**
  77  * ww_mutex_init - initialize the w/w mutex
  78  * @lock: the mutex to be initialized
  79  * @ww_class: the w/w class the mutex should belong to
  80  *
  81  * Initialize the w/w mutex to unlocked state and associate it with the given
  82  * class.
  83  *
  84  * It is not allowed to initialize an already locked mutex.
  85  */
  86 static inline void ww_mutex_init(struct ww_mutex *lock,
  87                                  struct ww_class *ww_class)
  88 {
  89         __mutex_init(&lock->base, ww_class->mutex_name, &ww_class->mutex_key);
  90         lock->ctx = NULL;
  91 #ifdef CONFIG_DEBUG_MUTEXES
  92         lock->ww_class = ww_class;
  93 #endif
  94 }
  95
  96 /**
  97  * ww_acquire_init - initialize a w/w acquire context
  98  * @ctx: w/w acquire context to initialize
  99  * @ww_class: w/w class of the context
 100  *
 101  * Initializes an context to acquire multiple mutexes of the given w/w class.
 102  *
 103  * Context-based w/w mutex acquiring can be done in any order whatsoever within
 104  * a given lock class. Deadlocks will be detected and handled with the
 105  * wait/wound logic.
 106  *
 107  * Mixing of context-based w/w mutex acquiring and single w/w mutex locking can
 108  * result in undetected deadlocks and is so forbidden. Mixing different contexts
 109  * for the same w/w class when acquiring mutexes can also result in undetected
 110  * deadlocks, and is hence also forbidden. Both types of abuse will be caught by
 111  * enabling CONFIG_PROVE_LOCKING.
 112  *
 113  * Nesting of acquire contexts for _different_ w/w classes is possible, subject
 114  * to the usual locking rules between different lock classes.
 115  *
 116  * An acquire context must be released with ww_acquire_fini by the same task
 117  * before the memory is freed. It is recommended to allocate the context itself
 118  * on the stack.
 119  */
 120 static inline void ww_acquire_init(struct ww_acquire_ctx *ctx,
 121                                    struct ww_class *ww_class)
 122 {
 123         ctx->task = current;
 124         ctx->stamp = atomic_long_inc_return_relaxed(&ww_class->stamp);
 125         ctx->acquired = 0;
 126 #ifdef CONFIG_DEBUG_MUTEXES
 127         ctx->ww_class = ww_class;
 128         ctx->done_acquire = 0;
 129         ctx->contending_lock = NULL;
 130 #endif
 131 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 132         debug_check_no_locks_freed((void *)ctx, sizeof(*ctx));
 133         lockdep_init_map(&ctx->dep_map, ww_class->acquire_name,
 134                          &ww_class->acquire_key, 0);
 135         mutex_acquire(&ctx->dep_map, 0, 0, _RET_IP_);
 136 #endif
 137 #ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
 138         ctx->deadlock_inject_interval = 1;
 139         ctx->deadlock_inject_countdown = ctx->stamp & 0xf;
 140 #endif
 141 }
 142
 143 /**
 144  * ww_acquire_done - marks the end of the acquire phase
 145  * @ctx: the acquire context
 146  *
 147  * Marks the end of the acquire phase, any further w/w mutex lock calls using
 148  * this context are forbidden.
 149  *
 150  * Calling this function is optional, it is just useful to document w/w mutex
 151  * code and clearly designated the acquire phase from actually using the locked
 152  * data structures.
 153  */
 154 static inline void ww_acquire_done(struct ww_acquire_ctx *ctx)
 155 {
 156 #ifdef CONFIG_DEBUG_MUTEXES
 157         lockdep_assert_held(ctx);
 158
 159         DEBUG_LOCKS_WARN_ON(ctx->done_acquire);
 160         ctx->done_acquire = 1;
 161 #endif
 162 }
 163
 164 /**
 165  * ww_acquire_fini - releases a w/w acquire context
 166  * @ctx: the acquire context to free
 167  *
 168  * Releases a w/w acquire context. This must be called _after_ all acquired w/w
 169  * mutexes have been released with ww_mutex_unlock.
 170  */
 171 static inline void ww_acquire_fini(struct ww_acquire_ctx *ctx)
 172 {
 173 #ifdef CONFIG_DEBUG_MUTEXES
 174         mutex_release(&ctx->dep_map, 0, _THIS_IP_);
 175
 176         DEBUG_LOCKS_WARN_ON(ctx->acquired);
 177         if (!IS_ENABLED(CONFIG_PROVE_LOCKING))
 178                 /*
 179                  * lockdep will normally handle this,
 180                  * but fail without anyway
 181                  */
 182                 ctx->done_acquire = 1;
 183
 184         if (!IS_ENABLED(CONFIG_DEBUG_LOCK_ALLOC))
 185                 /* ensure ww_acquire_fini will still fail if called twice */
 186                 ctx->acquired = ~0U;
 187 #endif
 188 }
 189
 190 /**
 191  * ww_mutex_lock - acquire the w/w mutex
 192  * @lock: the mutex to be acquired
 193  * @ctx: w/w acquire context, or NULL to acquire only a single lock.
 194  *
 195  * Lock the w/w mutex exclusively for this task.
 196  *
 197  * Deadlocks within a given w/w class of locks are detected and handled with the
 198  * wait/wound algorithm. If the lock isn't immediately avaiable this function
 199  * will either sleep until it is (wait case). Or it selects the current context
 200  * for backing off by returning -EDEADLK (wound case). Trying to acquire the
 201  * same lock with the same context twice is also detected and signalled by
 202  * returning -EALREADY. Returns 0 if the mutex was successfully acquired.
 203  *
 204  * In the wound case the caller must release all currently held w/w mutexes for
 205  * the given context and then wait for this contending lock to be available by
 206  * calling ww_mutex_lock_slow. Alternatively callers can opt to not acquire this
 207  * lock and proceed with trying to acquire further w/w mutexes (e.g. when
 208  * scanning through lru lists trying to free resources).
 209  *
 210  * The mutex must later on be released by the same task that
 211  * acquired it. The task may not exit without first unlocking the mutex. Also,
 212  * kernel memory where the mutex resides must not be freed with the mutex still
 213  * locked. The mutex must first be initialized (or statically defined) before it
 214  * can be locked. memset()-ing the mutex to 0 is not allowed. The mutex must be
 215  * of the same w/w lock class as was used to initialize the acquire context.
 216  *
 217  * A mutex acquired with this function must be released with ww_mutex_unlock.
 218  */
 219 extern int /* __must_check */ ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx);
 220
 221 /**
 222  * ww_mutex_lock_interruptible - acquire the w/w mutex, interruptible
 223  * @lock: the mutex to be acquired
 224  * @ctx: w/w acquire context
 225  *
 226  * Lock the w/w mutex exclusively for this task.
 227  *
 228  * Deadlocks within a given w/w class of locks are detected and handled with the
 229  * wait/wound algorithm. If the lock isn't immediately avaiable this function
 230  * will either sleep until it is (wait case). Or it selects the current context
 231  * for backing off by returning -EDEADLK (wound case). Trying to acquire the
 232  * same lock with the same context twice is also detected and signalled by
 233  * returning -EALREADY. Returns 0 if the mutex was successfully acquired. If a
 234  * signal arrives while waiting for the lock then this function returns -EINTR.
 235  *
 236  * In the wound case the caller must release all currently held w/w mutexes for
 237  * the given context and then wait for this contending lock to be available by
 238  * calling ww_mutex_lock_slow_interruptible. Alternatively callers can opt to
 239  * not acquire this lock and proceed with trying to acquire further w/w mutexes
 240  * (e.g. when scanning through lru lists trying to free resources).
 241  *
 242  * The mutex must later on be released by the same task that
 243  * acquired it. The task may not exit without first unlocking the mutex. Also,
 244  * kernel memory where the mutex resides must not be freed with the mutex still
 245  * locked. The mutex must first be initialized (or statically defined) before it
 246  * can be locked. memset()-ing the mutex to 0 is not allowed. The mutex must be
 247  * of the same w/w lock class as was used to initialize the acquire context.
 248  *
 249  * A mutex acquired with this function must be released with ww_mutex_unlock.
 250  */
 251 extern int __must_check ww_mutex_lock_interruptible(struct ww_mutex *lock,
 252                                                     struct ww_acquire_ctx *ctx);
 253
 254 /**
 255  * ww_mutex_lock_slow - slowpath acquiring of the w/w mutex
 256  * @lock: the mutex to be acquired
 257  * @ctx: w/w acquire context
 258  *
 259  * Acquires a w/w mutex with the given context after a wound case. This function
 260  * will sleep until the lock becomes available.
 261  *
 262  * The caller must have released all w/w mutexes already acquired with the
 263  * context and then call this function on the contended lock.
 264  *
 265  * Afterwards the caller may continue to (re)acquire the other w/w mutexes it
 266  * needs with ww_mutex_lock. Note that the -EALREADY return code from
 267  * ww_mutex_lock can be used to avoid locking this contended mutex twice.
 268  *
 269  * It is forbidden to call this function with any other w/w mutexes associated
 270  * with the context held. It is forbidden to call this on anything else than the
 271  * contending mutex.
 272  *
 273  * Note that the slowpath lock acquiring can also be done by calling
 274  * ww_mutex_lock directly. This function here is simply to help w/w mutex
 275  * locking code readability by clearly denoting the slowpath.
 276  */
 277 static inline void
 278 ww_mutex_lock_slow(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 279 {
 280         int ret;
 281 #ifdef CONFIG_DEBUG_MUTEXES
 282         DEBUG_LOCKS_WARN_ON(!ctx->contending_lock);
 283 #endif
 284         ret = ww_mutex_lock(lock, ctx);
 285         (void)ret;
 286 }
 287
 288 /**
 289  * ww_mutex_lock_slow_interruptible - slowpath acquiring of the w/w mutex, interruptible
 290  * @lock: the mutex to be acquired
 291  * @ctx: w/w acquire context
 292  *
 293  * Acquires a w/w mutex with the given context after a wound case. This function
 294  * will sleep until the lock becomes available and returns 0 when the lock has
 295  * been acquired. If a signal arrives while waiting for the lock then this
 296  * function returns -EINTR.
 297  *
 298  * The caller must have released all w/w mutexes already acquired with the
 299  * context and then call this function on the contended lock.
 300  *
 301  * Afterwards the caller may continue to (re)acquire the other w/w mutexes it
 302  * needs with ww_mutex_lock. Note that the -EALREADY return code from
 303  * ww_mutex_lock can be used to avoid locking this contended mutex twice.
 304  *
 305  * It is forbidden to call this function with any other w/w mutexes associated
 306  * with the given context held. It is forbidden to call this on anything else
 307  * than the contending mutex.
 308  *
 309  * Note that the slowpath lock acquiring can also be done by calling
 310  * ww_mutex_lock_interruptible directly. This function here is simply to help
 311  * w/w mutex locking code readability by clearly denoting the slowpath.
 312  */
 313 static inline int __must_check
 314 ww_mutex_lock_slow_interruptible(struct ww_mutex *lock,
 315                                  struct ww_acquire_ctx *ctx)
 316 {
 317 #ifdef CONFIG_DEBUG_MUTEXES
 318         DEBUG_LOCKS_WARN_ON(!ctx->contending_lock);
 319 #endif
 320         return ww_mutex_lock_interruptible(lock, ctx);
 321 }
 322
 323 extern void ww_mutex_unlock(struct ww_mutex *lock);
 324
 325 /**
 326  * ww_mutex_trylock - tries to acquire the w/w mutex without acquire context
 327  * @lock: mutex to lock
 328  *
 329  * Trylocks a mutex without acquire context, so no deadlock detection is
 330  * possible. Returns 1 if the mutex has been acquired successfully, 0 otherwise.
 331  */
 332 static inline int __must_check ww_mutex_trylock(struct ww_mutex *lock)
 333 {
 334         return mutex_trylock(&lock->base);
 335 }
 336
 337 /***
 338  * ww_mutex_destroy - mark a w/w mutex unusable
 339  * @lock: the mutex to be destroyed
 340  *
 341  * This function marks the mutex uninitialized, and any subsequent
 342  * use of the mutex is forbidden. The mutex must not be locked when
 343  * this function is called.
 344  */
 345 static inline void ww_mutex_destroy(struct ww_mutex *lock)
 346 {
 347         mutex_destroy(&lock->base);
 348 }
 349
 350 /**
 351  * ww_mutex_is_locked - is the w/w mutex locked
 352  * @lock: the mutex to be queried
 353  *
 354  * Returns 1 if the mutex is locked, 0 if unlocked.
 355  */
 356 static inline bool ww_mutex_is_locked(struct ww_mutex *lock)
 357 {
 358         return mutex_is_locked(&lock->base);
 359 }
 360
 361 #endif