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  * Wait/Die implementation:
  10  *  Copyright (C) 2013 Canonical Ltd.
  11  * Choice of algorithm:
  12  *  Copyright (C) 2018 WMWare Inc.
  13  *
  14  * This file contains the main data structure and API definitions.
  15  */
  16
  17 #ifndef __LINUX_WW_MUTEX_H
  18 #define __LINUX_WW_MUTEX_H
  19
  20 #include <linux/mutex.h>
  21 #include <linux/rtmutex.h>
  22
  23 #if defined(CONFIG_DEBUG_MUTEXES) || \
  24    (defined(CONFIG_PREEMPT_RT) && defined(CONFIG_DEBUG_RT_MUTEXES))
  25 #define DEBUG_WW_MUTEXES
  26 #endif
  27
  28 #ifndef CONFIG_PREEMPT_RT
  29 #define WW_MUTEX_BASE                   mutex
  30 #define ww_mutex_base_init(l,n,k)       __mutex_init(l,n,k)
  31 #define ww_mutex_base_trylock(l)        mutex_trylock(l)
  32 #define ww_mutex_base_is_locked(b)      mutex_is_locked((b))
  33 #else
  34 #define WW_MUTEX_BASE                   rt_mutex
  35 #define ww_mutex_base_init(l,n,k)       __rt_mutex_init(l,n,k)
  36 #define ww_mutex_base_trylock(l)        rt_mutex_trylock(l)
  37 #define ww_mutex_base_is_locked(b)      rt_mutex_base_is_locked(&(b)->rtmutex)
  38 #endif
  39
  40 struct ww_class {
  41         atomic_long_t stamp;
  42         struct lock_class_key acquire_key;
  43         struct lock_class_key mutex_key;
  44         const char *acquire_name;
  45         const char *mutex_name;
  46         unsigned int is_wait_die;
  47 };
  48
  49 struct ww_mutex {
  50         struct WW_MUTEX_BASE base;
  51         struct ww_acquire_ctx *ctx;
  52 #ifdef DEBUG_WW_MUTEXES
  53         struct ww_class *ww_class;
  54 #endif
  55 };
  56
  57 struct ww_acquire_ctx {
  58         struct task_struct *task;
  59         unsigned long stamp;
  60         unsigned int acquired;
  61         unsigned short wounded;
  62         unsigned short is_wait_die;
  63 #ifdef DEBUG_WW_MUTEXES
  64         unsigned int done_acquire;
  65         struct ww_class *ww_class;
  66         void *contending_lock;
  67 #endif
  68 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  69         struct lockdep_map dep_map;
  70 #endif
  71 #ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
  72         unsigned int deadlock_inject_interval;
  73         unsigned int deadlock_inject_countdown;
  74 #endif
  75 };
  76
  77 #define __WW_CLASS_INITIALIZER(ww_class, _is_wait_die)      \
  78                 { .stamp = ATOMIC_LONG_INIT(0) \
  79                 , .acquire_name = #ww_class "_acquire" \
  80                 , .mutex_name = #ww_class "_mutex" \
  81                 , .is_wait_die = _is_wait_die }
  82
  83 #define DEFINE_WD_CLASS(classname) \
  84         struct ww_class classname = __WW_CLASS_INITIALIZER(classname, 1)
  85
  86 #define DEFINE_WW_CLASS(classname) \
  87         struct ww_class classname = __WW_CLASS_INITIALIZER(classname, 0)
  88
  89 /**
  90  * ww_mutex_init - initialize the w/w mutex
  91  * @lock: the mutex to be initialized
  92  * @ww_class: the w/w class the mutex should belong to
  93  *
  94  * Initialize the w/w mutex to unlocked state and associate it with the given
  95  * class. Static define macro for w/w mutex is not provided and this function
  96  * is the only way to properly initialize the w/w mutex.
  97  *
  98  * It is not allowed to initialize an already locked mutex.
  99  */
 100 static inline void ww_mutex_init(struct ww_mutex *lock,
 101                                  struct ww_class *ww_class)
 102 {
 103         ww_mutex_base_init(&lock->base, ww_class->mutex_name, &ww_class->mutex_key);
 104         lock->ctx = NULL;
 105 #ifdef DEBUG_WW_MUTEXES
 106         lock->ww_class = ww_class;
 107 #endif
 108 }
 109
 110 /**
 111  * ww_acquire_init - initialize a w/w acquire context
 112  * @ctx: w/w acquire context to initialize
 113  * @ww_class: w/w class of the context
 114  *
 115  * Initializes an context to acquire multiple mutexes of the given w/w class.
 116  *
 117  * Context-based w/w mutex acquiring can be done in any order whatsoever within
 118  * a given lock class. Deadlocks will be detected and handled with the
 119  * wait/die logic.
 120  *
 121  * Mixing of context-based w/w mutex acquiring and single w/w mutex locking can
 122  * result in undetected deadlocks and is so forbidden. Mixing different contexts
 123  * for the same w/w class when acquiring mutexes can also result in undetected
 124  * deadlocks, and is hence also forbidden. Both types of abuse will be caught by
 125  * enabling CONFIG_PROVE_LOCKING.
 126  *
 127  * Nesting of acquire contexts for _different_ w/w classes is possible, subject
 128  * to the usual locking rules between different lock classes.
 129  *
 130  * An acquire context must be released with ww_acquire_fini by the same task
 131  * before the memory is freed. It is recommended to allocate the context itself
 132  * on the stack.
 133  */
 134 static inline void ww_acquire_init(struct ww_acquire_ctx *ctx,
 135                                    struct ww_class *ww_class)
 136 {
 137         ctx->task = current;
 138         ctx->stamp = atomic_long_inc_return_relaxed(&ww_class->stamp);
 139         ctx->acquired = 0;
 140         ctx->wounded = false;
 141         ctx->is_wait_die = ww_class->is_wait_die;
 142 #ifdef DEBUG_WW_MUTEXES
 143         ctx->ww_class = ww_class;
 144         ctx->done_acquire = 0;
 145         ctx->contending_lock = NULL;
 146 #endif
 147 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 148         debug_check_no_locks_freed((void *)ctx, sizeof(*ctx));
 149         lockdep_init_map(&ctx->dep_map, ww_class->acquire_name,
 150                          &ww_class->acquire_key, 0);
 151         mutex_acquire(&ctx->dep_map, 0, 0, _RET_IP_);
 152 #endif
 153 #ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
 154         ctx->deadlock_inject_interval = 1;
 155         ctx->deadlock_inject_countdown = ctx->stamp & 0xf;
 156 #endif
 157 }
 158
 159 /**
 160  * ww_acquire_done - marks the end of the acquire phase
 161  * @ctx: the acquire context
 162  *
 163  * Marks the end of the acquire phase, any further w/w mutex lock calls using
 164  * this context are forbidden.
 165  *
 166  * Calling this function is optional, it is just useful to document w/w mutex
 167  * code and clearly designated the acquire phase from actually using the locked
 168  * data structures.
 169  */
 170 static inline void ww_acquire_done(struct ww_acquire_ctx *ctx)
 171 {
 172 #ifdef DEBUG_WW_MUTEXES
 173         lockdep_assert_held(ctx);
 174
 175         DEBUG_LOCKS_WARN_ON(ctx->done_acquire);
 176         ctx->done_acquire = 1;
 177 #endif
 178 }
 179
 180 /**
 181  * ww_acquire_fini - releases a w/w acquire context
 182  * @ctx: the acquire context to free
 183  *
 184  * Releases a w/w acquire context. This must be called _after_ all acquired w/w
 185  * mutexes have been released with ww_mutex_unlock.
 186  */
 187 static inline void ww_acquire_fini(struct ww_acquire_ctx *ctx)
 188 {
 189 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 190         mutex_release(&ctx->dep_map, _THIS_IP_);
 191 #endif
 192 #ifdef DEBUG_WW_MUTEXES
 193         DEBUG_LOCKS_WARN_ON(ctx->acquired);
 194         if (!IS_ENABLED(CONFIG_PROVE_LOCKING))
 195                 /*
 196                  * lockdep will normally handle this,
 197                  * but fail without anyway
 198                  */
 199                 ctx->done_acquire = 1;
 200
 201         if (!IS_ENABLED(CONFIG_DEBUG_LOCK_ALLOC))
 202                 /* ensure ww_acquire_fini will still fail if called twice */
 203                 ctx->acquired = ~0U;
 204 #endif
 205 }
 206
 207 /**
 208  * ww_mutex_lock - acquire the w/w mutex
 209  * @lock: the mutex to be acquired
 210  * @ctx: w/w acquire context, or NULL to acquire only a single lock.
 211  *
 212  * Lock the w/w mutex exclusively for this task.
 213  *
 214  * Deadlocks within a given w/w class of locks are detected and handled with the
 215  * wait/die algorithm. If the lock isn't immediately available this function
 216  * will either sleep until it is (wait case). Or it selects the current context
 217  * for backing off by returning -EDEADLK (die case). Trying to acquire the
 218  * same lock with the same context twice is also detected and signalled by
 219  * returning -EALREADY. Returns 0 if the mutex was successfully acquired.
 220  *
 221  * In the die case the caller must release all currently held w/w mutexes for
 222  * the given context and then wait for this contending lock to be available by
 223  * calling ww_mutex_lock_slow. Alternatively callers can opt to not acquire this
 224  * lock and proceed with trying to acquire further w/w mutexes (e.g. when
 225  * scanning through lru lists trying to free resources).
 226  *
 227  * The mutex must later on be released by the same task that
 228  * acquired it. The task may not exit without first unlocking the mutex. Also,
 229  * kernel memory where the mutex resides must not be freed with the mutex still
 230  * locked. The mutex must first be initialized (or statically defined) before it
 231  * can be locked. memset()-ing the mutex to 0 is not allowed. The mutex must be
 232  * of the same w/w lock class as was used to initialize the acquire context.
 233  *
 234  * A mutex acquired with this function must be released with ww_mutex_unlock.
 235  */
 236 extern int /* __must_check */ ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx);
 237
 238 /**
 239  * ww_mutex_lock_interruptible - acquire the w/w mutex, interruptible
 240  * @lock: the mutex to be acquired
 241  * @ctx: w/w acquire context
 242  *
 243  * Lock the w/w mutex exclusively for this task.
 244  *
 245  * Deadlocks within a given w/w class of locks are detected and handled with the
 246  * wait/die algorithm. If the lock isn't immediately available this function
 247  * will either sleep until it is (wait case). Or it selects the current context
 248  * for backing off by returning -EDEADLK (die case). Trying to acquire the
 249  * same lock with the same context twice is also detected and signalled by
 250  * returning -EALREADY. Returns 0 if the mutex was successfully acquired. If a
 251  * signal arrives while waiting for the lock then this function returns -EINTR.
 252  *
 253  * In the die case the caller must release all currently held w/w mutexes for
 254  * the given context and then wait for this contending lock to be available by
 255  * calling ww_mutex_lock_slow_interruptible. Alternatively callers can opt to
 256  * not acquire this lock and proceed with trying to acquire further w/w mutexes
 257  * (e.g. when scanning through lru lists trying to free resources).
 258  *
 259  * The mutex must later on be released by the same task that
 260  * acquired it. The task may not exit without first unlocking the mutex. Also,
 261  * kernel memory where the mutex resides must not be freed with the mutex still
 262  * locked. The mutex must first be initialized (or statically defined) before it
 263  * can be locked. memset()-ing the mutex to 0 is not allowed. The mutex must be
 264  * of the same w/w lock class as was used to initialize the acquire context.
 265  *
 266  * A mutex acquired with this function must be released with ww_mutex_unlock.
 267  */
 268 extern int __must_check ww_mutex_lock_interruptible(struct ww_mutex *lock,
 269                                                     struct ww_acquire_ctx *ctx);
 270
 271 /**
 272  * ww_mutex_lock_slow - slowpath acquiring of the w/w mutex
 273  * @lock: the mutex to be acquired
 274  * @ctx: w/w acquire context
 275  *
 276  * Acquires a w/w mutex with the given context after a die case. This function
 277  * will sleep until the lock becomes available.
 278  *
 279  * The caller must have released all w/w mutexes already acquired with the
 280  * context and then call this function on the contended lock.
 281  *
 282  * Afterwards the caller may continue to (re)acquire the other w/w mutexes it
 283  * needs with ww_mutex_lock. Note that the -EALREADY return code from
 284  * ww_mutex_lock can be used to avoid locking this contended mutex twice.
 285  *
 286  * It is forbidden to call this function with any other w/w mutexes associated
 287  * with the context held. It is forbidden to call this on anything else than the
 288  * contending mutex.
 289  *
 290  * Note that the slowpath lock acquiring can also be done by calling
 291  * ww_mutex_lock directly. This function here is simply to help w/w mutex
 292  * locking code readability by clearly denoting the slowpath.
 293  */
 294 static inline void
 295 ww_mutex_lock_slow(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 296 {
 297         int ret;
 298 #ifdef DEBUG_WW_MUTEXES
 299         DEBUG_LOCKS_WARN_ON(!ctx->contending_lock);
 300 #endif
 301         ret = ww_mutex_lock(lock, ctx);
 302         (void)ret;
 303 }
 304
 305 /**
 306  * ww_mutex_lock_slow_interruptible - slowpath acquiring of the w/w mutex, interruptible
 307  * @lock: the mutex to be acquired
 308  * @ctx: w/w acquire context
 309  *
 310  * Acquires a w/w mutex with the given context after a die case. This function
 311  * will sleep until the lock becomes available and returns 0 when the lock has
 312  * been acquired. If a signal arrives while waiting for the lock then this
 313  * function returns -EINTR.
 314  *
 315  * The caller must have released all w/w mutexes already acquired with the
 316  * context and then call this function on the contended lock.
 317  *
 318  * Afterwards the caller may continue to (re)acquire the other w/w mutexes it
 319  * needs with ww_mutex_lock. Note that the -EALREADY return code from
 320  * ww_mutex_lock can be used to avoid locking this contended mutex twice.
 321  *
 322  * It is forbidden to call this function with any other w/w mutexes associated
 323  * with the given context held. It is forbidden to call this on anything else
 324  * than the contending mutex.
 325  *
 326  * Note that the slowpath lock acquiring can also be done by calling
 327  * ww_mutex_lock_interruptible directly. This function here is simply to help
 328  * w/w mutex locking code readability by clearly denoting the slowpath.
 329  */
 330 static inline int __must_check
 331 ww_mutex_lock_slow_interruptible(struct ww_mutex *lock,
 332                                  struct ww_acquire_ctx *ctx)
 333 {
 334 #ifdef DEBUG_WW_MUTEXES
 335         DEBUG_LOCKS_WARN_ON(!ctx->contending_lock);
 336 #endif
 337         return ww_mutex_lock_interruptible(lock, ctx);
 338 }
 339
 340 extern void ww_mutex_unlock(struct ww_mutex *lock);
 341
 342 /**
 343  * ww_mutex_trylock - tries to acquire the w/w mutex without acquire context
 344  * @lock: mutex to lock
 345  *
 346  * Trylocks a mutex without acquire context, so no deadlock detection is
 347  * possible. Returns 1 if the mutex has been acquired successfully, 0 otherwise.
 348  */
 349 static inline int __must_check ww_mutex_trylock(struct ww_mutex *lock)
 350 {
 351         return ww_mutex_base_trylock(&lock->base);
 352 }
 353
 354 /***
 355  * ww_mutex_destroy - mark a w/w mutex unusable
 356  * @lock: the mutex to be destroyed
 357  *
 358  * This function marks the mutex uninitialized, and any subsequent
 359  * use of the mutex is forbidden. The mutex must not be locked when
 360  * this function is called.
 361  */
 362 static inline void ww_mutex_destroy(struct ww_mutex *lock)
 363 {
 364 #ifndef CONFIG_PREEMPT_RT
 365         mutex_destroy(&lock->base);
 366 #endif
 367 }
 368
 369 /**
 370  * ww_mutex_is_locked - is the w/w mutex locked
 371  * @lock: the mutex to be queried
 372  *
 373  * Returns 1 if the mutex is locked, 0 if unlocked.
 374  */
 375 static inline bool ww_mutex_is_locked(struct ww_mutex *lock)
 376 {
 377         return ww_mutex_base_is_locked(&lock->base);
 378 }
 379
 380 #endif