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 /* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Wound/Wait Mutexes: blocking mutual exclusion locks with deadlock avoidance
  *
  * Original mutex implementation started by Ingo Molnar:
  *
  *  Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
  *
  * Wait/Die implementation:
  *  Copyright (C) 2013 Canonical Ltd.
  * Choice of algorithm:
  *  Copyright (C) 2018 WMWare Inc.
  *
  * This file contains the main data structure and API definitions.
  */
 
 #ifndef __LINUX_WW_MUTEX_H
 #define __LINUX_WW_MUTEX_H
 
 #include <linux/mutex.h>
 #include <linux/rtmutex.h>
 
 #if defined(CONFIG_DEBUG_MUTEXES) || \
    (defined(CONFIG_PREEMPT_RT) && defined(CONFIG_DEBUG_RT_MUTEXES))
 #define DEBUG_WW_MUTEXES
 #endif
 
 #ifndef CONFIG_PREEMPT_RT
 #define WW_MUTEX_BASE           mutex
 #define ww_mutex_base_init(l,n,k)   __mutex_init(l,n,k)
 #define ww_mutex_base_is_locked(b)  mutex_is_locked((b))
 #else
 #define WW_MUTEX_BASE           rt_mutex
 #define ww_mutex_base_init(l,n,k)   __rt_mutex_init(l,n,k)
 #define ww_mutex_base_is_locked(b)  rt_mutex_base_is_locked(&(b)->rtmutex)
 #endif
 
 struct ww_class {
     atomic_long_t stamp;
     struct lock_class_key acquire_key;
     struct lock_class_key mutex_key;
     const char *acquire_name;
     const char *mutex_name;
     unsigned int is_wait_die;
 };
 
 struct ww_mutex {
     struct WW_MUTEX_BASE base;
     struct ww_acquire_ctx *ctx;
 #ifdef DEBUG_WW_MUTEXES
     struct ww_class *ww_class;
 #endif
 };
 
 struct ww_acquire_ctx {
     struct task_struct *task;
     unsigned long stamp;
     unsigned int acquired;
     unsigned short wounded;
     unsigned short is_wait_die;
 #ifdef DEBUG_WW_MUTEXES
     unsigned int done_acquire;
     struct ww_class *ww_class;
     void *contending_lock;
 #endif
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
     struct lockdep_map dep_map;
 #endif
 #ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
     unsigned int deadlock_inject_interval;
     unsigned int deadlock_inject_countdown;
 #endif
 };
 
 #define __WW_CLASS_INITIALIZER(ww_class, _is_wait_die)      \
         { .stamp = ATOMIC_LONG_INIT(0) \
         , .acquire_name = #ww_class "_acquire" \
         , .mutex_name = #ww_class "_mutex" \
         , .is_wait_die = _is_wait_die }
 
 #define DEFINE_WD_CLASS(classname) \
     struct ww_class classname = __WW_CLASS_INITIALIZER(classname, 1)
 
 #define DEFINE_WW_CLASS(classname) \
     struct ww_class classname = __WW_CLASS_INITIALIZER(classname, 0)
 
 /**
  * ww_mutex_init - initialize the w/w mutex
  * @lock: the mutex to be initialized
  * @ww_class: the w/w class the mutex should belong to
  *
  * Initialize the w/w mutex to unlocked state and associate it with the given
  * class. Static define macro for w/w mutex is not provided and this function
  * is the only way to properly initialize the w/w mutex.
  *
  * It is not allowed to initialize an already locked mutex.
  */
 static inline void ww_mutex_init(struct ww_mutex *lock,
                  struct ww_class *ww_class)
 {
     ww_mutex_base_init(&lock->base, ww_class->mutex_name, &ww_class->mutex_key);
     lock->ctx = NULL;
 #ifdef DEBUG_WW_MUTEXES
     lock->ww_class = ww_class;
 #endif
 }
 
 /**
  * ww_acquire_init - initialize a w/w acquire context
  * @ctx: w/w acquire context to initialize
  * @ww_class: w/w class of the context
  *
  * Initializes an context to acquire multiple mutexes of the given w/w class.
  *
  * Context-based w/w mutex acquiring can be done in any order whatsoever within
  * a given lock class. Deadlocks will be detected and handled with the
  * wait/die logic.
  *
  * Mixing of context-based w/w mutex acquiring and single w/w mutex locking can
  * result in undetected deadlocks and is so forbidden. Mixing different contexts
  * for the same w/w class when acquiring mutexes can also result in undetected
  * deadlocks, and is hence also forbidden. Both types of abuse will be caught by
  * enabling CONFIG_PROVE_LOCKING.
  *
  * Nesting of acquire contexts for _different_ w/w classes is possible, subject
  * to the usual locking rules between different lock classes.
  *
  * An acquire context must be released with ww_acquire_fini by the same task
  * before the memory is freed. It is recommended to allocate the context itself
  * on the stack.
  */
 static inline void ww_acquire_init(struct ww_acquire_ctx *ctx,
                    struct ww_class *ww_class)
 {
     ctx->task = current;
     ctx->stamp = atomic_long_inc_return_relaxed(&ww_class->stamp);
     ctx->acquired = 0;
     ctx->wounded = false;
     ctx->is_wait_die = ww_class->is_wait_die;
 #ifdef DEBUG_WW_MUTEXES
     ctx->ww_class = ww_class;
     ctx->done_acquire = 0;
     ctx->contending_lock = NULL;
 #endif
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
     debug_check_no_locks_freed((void *)ctx, sizeof(*ctx));
     lockdep_init_map(&ctx->dep_map, ww_class->acquire_name,
              &ww_class->acquire_key, 0);
     mutex_acquire(&ctx->dep_map, 0, 0, _RET_IP_);
 #endif
 #ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
     ctx->deadlock_inject_interval = 1;
     ctx->deadlock_inject_countdown = ctx->stamp & 0xf;
 #endif
 }
 
 /**
  * ww_acquire_done - marks the end of the acquire phase
  * @ctx: the acquire context
  *
  * Marks the end of the acquire phase, any further w/w mutex lock calls using
  * this context are forbidden.
  *
  * Calling this function is optional, it is just useful to document w/w mutex
  * code and clearly designated the acquire phase from actually using the locked
  * data structures.
  */
 static inline void ww_acquire_done(struct ww_acquire_ctx *ctx)
 {
 #ifdef DEBUG_WW_MUTEXES
     lockdep_assert_held(ctx);
 
     DEBUG_LOCKS_WARN_ON(ctx->done_acquire);
     ctx->done_acquire = 1;
 #endif
 }
 
 /**
  * ww_acquire_fini - releases a w/w acquire context
  * @ctx: the acquire context to free
  *
  * Releases a w/w acquire context. This must be called _after_ all acquired w/w
  * mutexes have been released with ww_mutex_unlock.
  */
 static inline void ww_acquire_fini(struct ww_acquire_ctx *ctx)
 {
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
     mutex_release(&ctx->dep_map, _THIS_IP_);
 #endif
 #ifdef DEBUG_WW_MUTEXES
     DEBUG_LOCKS_WARN_ON(ctx->acquired);
     if (!IS_ENABLED(CONFIG_PROVE_LOCKING))
         /*
          * lockdep will normally handle this,
          * but fail without anyway
          */
         ctx->done_acquire = 1;
 
     if (!IS_ENABLED(CONFIG_DEBUG_LOCK_ALLOC))
         /* ensure ww_acquire_fini will still fail if called twice */
         ctx->acquired = ~0U;
 #endif
 }
 
 /**
  * ww_mutex_lock - acquire the w/w mutex
  * @lock: the mutex to be acquired
  * @ctx: w/w acquire context, or NULL to acquire only a single lock.
  *
  * Lock the w/w mutex exclusively for this task.
  *
  * Deadlocks within a given w/w class of locks are detected and handled with the
  * wait/die algorithm. If the lock isn't immediately available this function
  * will either sleep until it is (wait case). Or it selects the current context
  * for backing off by returning -EDEADLK (die case). Trying to acquire the
  * same lock with the same context twice is also detected and signalled by
  * returning -EALREADY. Returns 0 if the mutex was successfully acquired.
  *
  * In the die case the caller must release all currently held w/w mutexes for
  * the given context and then wait for this contending lock to be available by
  * calling ww_mutex_lock_slow. Alternatively callers can opt to not acquire this
  * lock and proceed with trying to acquire further w/w mutexes (e.g. when
  * scanning through lru lists trying to free resources).
  *
  * The mutex must later on be released by the same task that
  * acquired it. The task may not exit without first unlocking the mutex. Also,
  * kernel memory where the mutex resides must not be freed with the mutex still
  * locked. The mutex must first be initialized (or statically defined) before it
  * can be locked. memset()-ing the mutex to 0 is not allowed. The mutex must be
  * of the same w/w lock class as was used to initialize the acquire context.
  *
  * A mutex acquired with this function must be released with ww_mutex_unlock.
  */
 extern int /* __must_check */ ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx);
 
 /**
  * ww_mutex_lock_interruptible - acquire the w/w mutex, interruptible
  * @lock: the mutex to be acquired
  * @ctx: w/w acquire context
  *
  * Lock the w/w mutex exclusively for this task.
  *
  * Deadlocks within a given w/w class of locks are detected and handled with the
  * wait/die algorithm. If the lock isn't immediately available this function
  * will either sleep until it is (wait case). Or it selects the current context
  * for backing off by returning -EDEADLK (die case). Trying to acquire the
  * same lock with the same context twice is also detected and signalled by
  * returning -EALREADY. Returns 0 if the mutex was successfully acquired. If a
  * signal arrives while waiting for the lock then this function returns -EINTR.
  *
  * In the die case the caller must release all currently held w/w mutexes for
  * the given context and then wait for this contending lock to be available by
  * calling ww_mutex_lock_slow_interruptible. Alternatively callers can opt to
  * not acquire this lock and proceed with trying to acquire further w/w mutexes
  * (e.g. when scanning through lru lists trying to free resources).
  *
  * The mutex must later on be released by the same task that
  * acquired it. The task may not exit without first unlocking the mutex. Also,
  * kernel memory where the mutex resides must not be freed with the mutex still
  * locked. The mutex must first be initialized (or statically defined) before it
  * can be locked. memset()-ing the mutex to 0 is not allowed. The mutex must be
  * of the same w/w lock class as was used to initialize the acquire context.
  *
  * A mutex acquired with this function must be released with ww_mutex_unlock.
  */
 extern int __must_check ww_mutex_lock_interruptible(struct ww_mutex *lock,
                             struct ww_acquire_ctx *ctx);
 
 /**
  * ww_mutex_lock_slow - slowpath acquiring of the w/w mutex
  * @lock: the mutex to be acquired
  * @ctx: w/w acquire context
  *
  * Acquires a w/w mutex with the given context after a die case. This function
  * will sleep until the lock becomes available.
  *
  * The caller must have released all w/w mutexes already acquired with the
  * context and then call this function on the contended lock.
  *
  * Afterwards the caller may continue to (re)acquire the other w/w mutexes it
  * needs with ww_mutex_lock. Note that the -EALREADY return code from
  * ww_mutex_lock can be used to avoid locking this contended mutex twice.
  *
  * It is forbidden to call this function with any other w/w mutexes associated
  * with the context held. It is forbidden to call this on anything else than the
  * contending mutex.
  *
  * Note that the slowpath lock acquiring can also be done by calling
  * ww_mutex_lock directly. This function here is simply to help w/w mutex
  * locking code readability by clearly denoting the slowpath.
  */
 static inline void
 ww_mutex_lock_slow(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 {
     int ret;
 #ifdef DEBUG_WW_MUTEXES
     DEBUG_LOCKS_WARN_ON(!ctx->contending_lock);
 #endif
     ret = ww_mutex_lock(lock, ctx);
     (void)ret;
 }
 
 /**
  * ww_mutex_lock_slow_interruptible - slowpath acquiring of the w/w mutex, interruptible
  * @lock: the mutex to be acquired
  * @ctx: w/w acquire context
  *
  * Acquires a w/w mutex with the given context after a die case. This function
  * will sleep until the lock becomes available and returns 0 when the lock has
  * been acquired. If a signal arrives while waiting for the lock then this
  * function returns -EINTR.
  *
  * The caller must have released all w/w mutexes already acquired with the
  * context and then call this function on the contended lock.
  *
  * Afterwards the caller may continue to (re)acquire the other w/w mutexes it
  * needs with ww_mutex_lock. Note that the -EALREADY return code from
  * ww_mutex_lock can be used to avoid locking this contended mutex twice.
  *
  * It is forbidden to call this function with any other w/w mutexes associated
  * with the given context held. It is forbidden to call this on anything else
  * than the contending mutex.
  *
  * Note that the slowpath lock acquiring can also be done by calling
  * ww_mutex_lock_interruptible directly. This function here is simply to help
  * w/w mutex locking code readability by clearly denoting the slowpath.
  */
 static inline int __must_check
 ww_mutex_lock_slow_interruptible(struct ww_mutex *lock,
                  struct ww_acquire_ctx *ctx)
 {
 #ifdef DEBUG_WW_MUTEXES
     DEBUG_LOCKS_WARN_ON(!ctx->contending_lock);
 #endif
     return ww_mutex_lock_interruptible(lock, ctx);
 }
 
 extern void ww_mutex_unlock(struct ww_mutex *lock);
 
 extern int __must_check ww_mutex_trylock(struct ww_mutex *lock,
                      struct ww_acquire_ctx *ctx);
 
 /***
  * ww_mutex_destroy - mark a w/w mutex unusable
  * @lock: the mutex to be destroyed
  *
  * This function marks the mutex uninitialized, and any subsequent
  * use of the mutex is forbidden. The mutex must not be locked when
  * this function is called.
  */
 static inline void ww_mutex_destroy(struct ww_mutex *lock)
 {
 #ifndef CONFIG_PREEMPT_RT
     mutex_destroy(&lock->base);
 #endif
 }
 
 /**
  * ww_mutex_is_locked - is the w/w mutex locked
  * @lock: the mutex to be queried
  *
  * Returns 1 if the mutex is locked, 0 if unlocked.
  */
 static inline bool ww_mutex_is_locked(struct ww_mutex *lock)
 {
     return ww_mutex_base_is_locked(&lock->base);
 }
 
 #endif

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