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