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_is_locked(b)      mutex_is_locked((b))
  32 #else
  33 #define WW_MUTEX_BASE                   rt_mutex
  34 #define ww_mutex_base_init(l,n,k)       __rt_mutex_init(l,n,k)
  35 #define ww_mutex_base_is_locked(b)      rt_mutex_base_is_locked(&(b)->rtmutex)
  36 #endif
  37
  38 struct ww_class {
  39         atomic_long_t stamp;
  40         struct lock_class_key acquire_key;
  41         struct lock_class_key mutex_key;
  42         const char *acquire_name;
  43         const char *mutex_name;
  44         unsigned int is_wait_die;
  45 };
  46
  47 struct ww_mutex {
  48         struct WW_MUTEX_BASE base;
  49         struct ww_acquire_ctx *ctx;
  50 #ifdef DEBUG_WW_MUTEXES
  51         struct ww_class *ww_class;
  52 #endif
  53 };
  54
  55 struct ww_acquire_ctx {
  56         struct task_struct *task;
  57         unsigned long stamp;
  58         unsigned int acquired;
  59         unsigned short wounded;
  60         unsigned short is_wait_die;
  61 #ifdef DEBUG_WW_MUTEXES
  62         unsigned int done_acquire;
  63         struct ww_class *ww_class;
  64         void *contending_lock;
  65 #endif
  66 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  67         struct lockdep_map dep_map;
  68         /**
  69          * @first_lock_dep_map: fake lockdep_map for first locked ww_mutex.
  70          *
  71          * lockdep requires the lockdep_map for the first locked ww_mutex
  72          * in a ww transaction to remain in memory until all ww_mutexes of
  73          * the transaction have been unlocked. Ensure this by keeping a
  74          * fake locked ww_mutex lockdep map between ww_acquire_init() and
  75          * ww_acquire_fini().
  76          */
  77         struct lockdep_map first_lock_dep_map;
  78 #endif
  79 #ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
  80         unsigned int deadlock_inject_interval;
  81         unsigned int deadlock_inject_countdown;
  82 #endif
  83 };
  84
  85 #define __WW_CLASS_INITIALIZER(ww_class, _is_wait_die)      \
  86                 { .stamp = ATOMIC_LONG_INIT(0) \
  87                 , .acquire_name = #ww_class "_acquire" \
  88                 , .mutex_name = #ww_class "_mutex" \
  89                 , .is_wait_die = _is_wait_die }
  90
  91 #define DEFINE_WD_CLASS(classname) \
  92         struct ww_class classname = __WW_CLASS_INITIALIZER(classname, 1)
  93
  94 #define DEFINE_WW_CLASS(classname) \
  95         struct ww_class classname = __WW_CLASS_INITIALIZER(classname, 0)
  96
  97 /**
  98  * ww_mutex_init - initialize the w/w mutex
  99  * @lock: the mutex to be initialized
 100  * @ww_class: the w/w class the mutex should belong to
 101  *
 102  * Initialize the w/w mutex to unlocked state and associate it with the given
 103  * class. Static define macro for w/w mutex is not provided and this function
 104  * is the only way to properly initialize the w/w mutex.
 105  *
 106  * It is not allowed to initialize an already locked mutex.
 107  */
 108 static inline void ww_mutex_init(struct ww_mutex *lock,
 109                                  struct ww_class *ww_class)
 110 {
 111         ww_mutex_base_init(&lock->base, ww_class->mutex_name, &ww_class->mutex_key);
 112         lock->ctx = NULL;
 113 #ifdef DEBUG_WW_MUTEXES
 114         lock->ww_class = ww_class;
 115 #endif
 116 }
 117
 118 /**
 119  * ww_acquire_init - initialize a w/w acquire context
 120  * @ctx: w/w acquire context to initialize
 121  * @ww_class: w/w class of the context
 122  *
 123  * Initializes an context to acquire multiple mutexes of the given w/w class.
 124  *
 125  * Context-based w/w mutex acquiring can be done in any order whatsoever within
 126  * a given lock class. Deadlocks will be detected and handled with the
 127  * wait/die logic.
 128  *
 129  * Mixing of context-based w/w mutex acquiring and single w/w mutex locking can
 130  * result in undetected deadlocks and is so forbidden. Mixing different contexts
 131  * for the same w/w class when acquiring mutexes can also result in undetected
 132  * deadlocks, and is hence also forbidden. Both types of abuse will be caught by
 133  * enabling CONFIG_PROVE_LOCKING.
 134  *
 135  * Nesting of acquire contexts for _different_ w/w classes is possible, subject
 136  * to the usual locking rules between different lock classes.
 137  *
 138  * An acquire context must be released with ww_acquire_fini by the same task
 139  * before the memory is freed. It is recommended to allocate the context itself
 140  * on the stack.
 141  */
 142 static inline void ww_acquire_init(struct ww_acquire_ctx *ctx,
 143                                    struct ww_class *ww_class)
 144 {
 145         ctx->task = current;
 146         ctx->stamp = atomic_long_inc_return_relaxed(&ww_class->stamp);
 147         ctx->acquired = 0;
 148         ctx->wounded = false;
 149         ctx->is_wait_die = ww_class->is_wait_die;
 150 #ifdef DEBUG_WW_MUTEXES
 151         ctx->ww_class = ww_class;
 152         ctx->done_acquire = 0;
 153         ctx->contending_lock = NULL;
 154 #endif
 155 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 156         debug_check_no_locks_freed((void *)ctx, sizeof(*ctx));
 157         lockdep_init_map(&ctx->dep_map, ww_class->acquire_name,
 158                          &ww_class->acquire_key, 0);
 159         lockdep_init_map(&ctx->first_lock_dep_map, ww_class->mutex_name,
 160                          &ww_class->mutex_key, 0);
 161         mutex_acquire(&ctx->dep_map, 0, 0, _RET_IP_);
 162         mutex_acquire_nest(&ctx->first_lock_dep_map, 0, 0, &ctx->dep_map, _RET_IP_);
 163 #endif
 164 #ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
 165         ctx->deadlock_inject_interval = 1;
 166         ctx->deadlock_inject_countdown = ctx->stamp & 0xf;
 167 #endif
 168 }
 169
 170 /**
 171  * ww_acquire_done - marks the end of the acquire phase
 172  * @ctx: the acquire context
 173  *
 174  * Marks the end of the acquire phase, any further w/w mutex lock calls using
 175  * this context are forbidden.
 176  *
 177  * Calling this function is optional, it is just useful to document w/w mutex
 178  * code and clearly designated the acquire phase from actually using the locked
 179  * data structures.
 180  */
 181 static inline void ww_acquire_done(struct ww_acquire_ctx *ctx)
 182 {
 183 #ifdef DEBUG_WW_MUTEXES
 184         lockdep_assert_held(ctx);
 185
 186         DEBUG_LOCKS_WARN_ON(ctx->done_acquire);
 187         ctx->done_acquire = 1;
 188 #endif
 189 }
 190
 191 /**
 192  * ww_acquire_fini - releases a w/w acquire context
 193  * @ctx: the acquire context to free
 194  *
 195  * Releases a w/w acquire context. This must be called _after_ all acquired w/w
 196  * mutexes have been released with ww_mutex_unlock.
 197  */
 198 static inline void ww_acquire_fini(struct ww_acquire_ctx *ctx)
 199 {
 200 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 201         mutex_release(&ctx->first_lock_dep_map, _THIS_IP_);
 202         mutex_release(&ctx->dep_map, _THIS_IP_);
 203 #endif
 204 #ifdef DEBUG_WW_MUTEXES
 205         DEBUG_LOCKS_WARN_ON(ctx->acquired);
 206         if (!IS_ENABLED(CONFIG_PROVE_LOCKING))
 207                 /*
 208                  * lockdep will normally handle this,
 209                  * but fail without anyway
 210                  */
 211                 ctx->done_acquire = 1;
 212
 213         if (!IS_ENABLED(CONFIG_DEBUG_LOCK_ALLOC))
 214                 /* ensure ww_acquire_fini will still fail if called twice */
 215                 ctx->acquired = ~0U;
 216 #endif
 217 }
 218
 219 /**
 220  * ww_mutex_lock - acquire the w/w mutex
 221  * @lock: the mutex to be acquired
 222  * @ctx: w/w acquire context, or NULL to acquire only a single lock.
 223  *
 224  * Lock the w/w mutex exclusively for this task.
 225  *
 226  * Deadlocks within a given w/w class of locks are detected and handled with the
 227  * wait/die algorithm. If the lock isn't immediately available this function
 228  * will either sleep until it is (wait case). Or it selects the current context
 229  * for backing off by returning -EDEADLK (die case). Trying to acquire the
 230  * same lock with the same context twice is also detected and signalled by
 231  * returning -EALREADY. Returns 0 if the mutex was successfully acquired.
 232  *
 233  * In the die case the caller must release all currently held w/w mutexes for
 234  * the given context and then wait for this contending lock to be available by
 235  * calling ww_mutex_lock_slow. Alternatively callers can opt to not acquire this
 236  * lock and proceed with trying to acquire further w/w mutexes (e.g. when
 237  * scanning through lru lists trying to free resources).
 238  *
 239  * The mutex must later on be released by the same task that
 240  * acquired it. The task may not exit without first unlocking the mutex. Also,
 241  * kernel memory where the mutex resides must not be freed with the mutex still
 242  * locked. The mutex must first be initialized (or statically defined) before it
 243  * can be locked. memset()-ing the mutex to 0 is not allowed. The mutex must be
 244  * of the same w/w lock class as was used to initialize the acquire context.
 245  *
 246  * A mutex acquired with this function must be released with ww_mutex_unlock.
 247  */
 248 extern int /* __must_check */ ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx);
 249
 250 /**
 251  * ww_mutex_lock_interruptible - acquire the w/w mutex, interruptible
 252  * @lock: the mutex to be acquired
 253  * @ctx: w/w acquire context
 254  *
 255  * Lock the w/w mutex exclusively for this task.
 256  *
 257  * Deadlocks within a given w/w class of locks are detected and handled with the
 258  * wait/die algorithm. If the lock isn't immediately available this function
 259  * will either sleep until it is (wait case). Or it selects the current context
 260  * for backing off by returning -EDEADLK (die case). Trying to acquire the
 261  * same lock with the same context twice is also detected and signalled by
 262  * returning -EALREADY. Returns 0 if the mutex was successfully acquired. If a
 263  * signal arrives while waiting for the lock then this function returns -EINTR.
 264  *
 265  * In the die case the caller must release all currently held w/w mutexes for
 266  * the given context and then wait for this contending lock to be available by
 267  * calling ww_mutex_lock_slow_interruptible. Alternatively callers can opt to
 268  * not acquire this lock and proceed with trying to acquire further w/w mutexes
 269  * (e.g. when scanning through lru lists trying to free resources).
 270  *
 271  * The mutex must later on be released by the same task that
 272  * acquired it. The task may not exit without first unlocking the mutex. Also,
 273  * kernel memory where the mutex resides must not be freed with the mutex still
 274  * locked. The mutex must first be initialized (or statically defined) before it
 275  * can be locked. memset()-ing the mutex to 0 is not allowed. The mutex must be
 276  * of the same w/w lock class as was used to initialize the acquire context.
 277  *
 278  * A mutex acquired with this function must be released with ww_mutex_unlock.
 279  */
 280 extern int __must_check ww_mutex_lock_interruptible(struct ww_mutex *lock,
 281                                                     struct ww_acquire_ctx *ctx);
 282
 283 /**
 284  * ww_mutex_lock_slow - slowpath acquiring of the w/w mutex
 285  * @lock: the mutex to be acquired
 286  * @ctx: w/w acquire context
 287  *
 288  * Acquires a w/w mutex with the given context after a die case. This function
 289  * will sleep until the lock becomes available.
 290  *
 291  * The caller must have released all w/w mutexes already acquired with the
 292  * context and then call this function on the contended lock.
 293  *
 294  * Afterwards the caller may continue to (re)acquire the other w/w mutexes it
 295  * needs with ww_mutex_lock. Note that the -EALREADY return code from
 296  * ww_mutex_lock can be used to avoid locking this contended mutex twice.
 297  *
 298  * It is forbidden to call this function with any other w/w mutexes associated
 299  * with the context held. It is forbidden to call this on anything else than the
 300  * contending mutex.
 301  *
 302  * Note that the slowpath lock acquiring can also be done by calling
 303  * ww_mutex_lock directly. This function here is simply to help w/w mutex
 304  * locking code readability by clearly denoting the slowpath.
 305  */
 306 static inline void
 307 ww_mutex_lock_slow(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 308 {
 309         int ret;
 310 #ifdef DEBUG_WW_MUTEXES
 311         DEBUG_LOCKS_WARN_ON(!ctx->contending_lock);
 312 #endif
 313         ret = ww_mutex_lock(lock, ctx);
 314         (void)ret;
 315 }
 316
 317 /**
 318  * ww_mutex_lock_slow_interruptible - slowpath acquiring of the w/w mutex, interruptible
 319  * @lock: the mutex to be acquired
 320  * @ctx: w/w acquire context
 321  *
 322  * Acquires a w/w mutex with the given context after a die case. This function
 323  * will sleep until the lock becomes available and returns 0 when the lock has
 324  * been acquired. If a signal arrives while waiting for the lock then this
 325  * function returns -EINTR.
 326  *
 327  * The caller must have released all w/w mutexes already acquired with the
 328  * context and then call this function on the contended lock.
 329  *
 330  * Afterwards the caller may continue to (re)acquire the other w/w mutexes it
 331  * needs with ww_mutex_lock. Note that the -EALREADY return code from
 332  * ww_mutex_lock can be used to avoid locking this contended mutex twice.
 333  *
 334  * It is forbidden to call this function with any other w/w mutexes associated
 335  * with the given context held. It is forbidden to call this on anything else
 336  * than the contending mutex.
 337  *
 338  * Note that the slowpath lock acquiring can also be done by calling
 339  * ww_mutex_lock_interruptible directly. This function here is simply to help
 340  * w/w mutex locking code readability by clearly denoting the slowpath.
 341  */
 342 static inline int __must_check
 343 ww_mutex_lock_slow_interruptible(struct ww_mutex *lock,
 344                                  struct ww_acquire_ctx *ctx)
 345 {
 346 #ifdef DEBUG_WW_MUTEXES
 347         DEBUG_LOCKS_WARN_ON(!ctx->contending_lock);
 348 #endif
 349         return ww_mutex_lock_interruptible(lock, ctx);
 350 }
 351
 352 extern void ww_mutex_unlock(struct ww_mutex *lock);
 353
 354 extern int __must_check ww_mutex_trylock(struct ww_mutex *lock,
 355                                          struct ww_acquire_ctx *ctx);
 356
 357 /***
 358  * ww_mutex_destroy - mark a w/w mutex unusable
 359  * @lock: the mutex to be destroyed
 360  *
 361  * This function marks the mutex uninitialized, and any subsequent
 362  * use of the mutex is forbidden. The mutex must not be locked when
 363  * this function is called.
 364  */
 365 static inline void ww_mutex_destroy(struct ww_mutex *lock)
 366 {
 367 #ifndef CONFIG_PREEMPT_RT
 368         mutex_destroy(&lock->base);
 369 #endif
 370 }
 371
 372 /**
 373  * ww_mutex_is_locked - is the w/w mutex locked
 374  * @lock: the mutex to be queried
 375  *
 376  * Returns 1 if the mutex is locked, 0 if unlocked.
 377  */
 378 static inline bool ww_mutex_is_locked(struct ww_mutex *lock)
 379 {
 380         return ww_mutex_base_is_locked(&lock->base);
 381 }
 382
 383 #endif