Line data    Source code

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