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 // SPDX-License-Identifier: GPL-2.0-only
 /*
  * kernel/locking/mutex.c
  *
  * Mutexes: blocking mutual exclusion locks
  *
  * Started by Ingo Molnar:
  *
  *  Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
  *
  * Many thanks to Arjan van de Ven, Thomas Gleixner, Steven Rostedt and
  * David Howells for suggestions and improvements.
  *
  *  - Adaptive spinning for mutexes by Peter Zijlstra. (Ported to mainline
  *    from the -rt tree, where it was originally implemented for rtmutexes
  *    by Steven Rostedt, based on work by Gregory Haskins, Peter Morreale
  *    and Sven Dietrich.
  *
  * Also see Documentation/locking/mutex-design.rst.
  */
 #include <linux/mutex.h>
 #include <linux/ww_mutex.h>
 #include <linux/sched/signal.h>
 #include <linux/sched/rt.h>
 #include <linux/sched/wake_q.h>
 #include <linux/sched/debug.h>
 #include <linux/export.h>
 #include <linux/spinlock.h>
 #include <linux/interrupt.h>
 #include <linux/debug_locks.h>
 #include <linux/osq_lock.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/lock.h>
 
 #ifndef CONFIG_PREEMPT_RT
 #include "mutex.h"
 
 #ifdef CONFIG_DEBUG_MUTEXES
 # define MUTEX_WARN_ON(cond) DEBUG_LOCKS_WARN_ON(cond)
 #else
 # define MUTEX_WARN_ON(cond)
 #endif
 
 void
 __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
 {
     atomic_long_set(&lock->owner, 0);
     raw_spin_lock_init(&lock->wait_lock);
     INIT_LIST_HEAD(&lock->wait_list);
 #ifdef CONFIG_MUTEX_SPIN_ON_OWNER
     osq_lock_init(&lock->osq);
 #endif
 
     debug_mutex_init(lock, name, key);
 }
 EXPORT_SYMBOL(__mutex_init);
 
 /*
  * @owner: contains: 'struct task_struct *' to the current lock owner,
  * NULL means not owned. Since task_struct pointers are aligned at
  * at least L1_CACHE_BYTES, we have low bits to store extra state.
  *
  * Bit0 indicates a non-empty waiter list; unlock must issue a wakeup.
  * Bit1 indicates unlock needs to hand the lock to the top-waiter
  * Bit2 indicates handoff has been done and we're waiting for pickup.
  */
 #define MUTEX_FLAG_WAITERS  0x01
 #define MUTEX_FLAG_HANDOFF  0x02
 #define MUTEX_FLAG_PICKUP   0x04
 
 #define MUTEX_FLAGS     0x07
 
 /*
  * Internal helper function; C doesn't allow us to hide it :/
  *
  * DO NOT USE (outside of mutex code).
  */
 static inline struct task_struct *__mutex_owner(struct mutex *lock)
 {
     return (struct task_struct *)(atomic_long_read(&lock->owner) & ~MUTEX_FLAGS);
 }
 
 static inline struct task_struct *__owner_task(unsigned long owner)
 {
     return (struct task_struct *)(owner & ~MUTEX_FLAGS);
 }
 
 bool mutex_is_locked(struct mutex *lock)
 {
     return __mutex_owner(lock) != NULL;
 }
 EXPORT_SYMBOL(mutex_is_locked);
 
 static inline unsigned long __owner_flags(unsigned long owner)
 {
     return owner & MUTEX_FLAGS;
 }
 
 /*
  * Returns: __mutex_owner(lock) on failure or NULL on success.
  */
 static inline struct task_struct *__mutex_trylock_common(struct mutex *lock, bool handoff)
 {
     unsigned long owner, curr = (unsigned long)current;
 
     owner = atomic_long_read(&lock->owner);
     for (;;) { /* must loop, can race against a flag */
         unsigned long flags = __owner_flags(owner);
         unsigned long task = owner & ~MUTEX_FLAGS;
 
         if (task) {
             if (flags & MUTEX_FLAG_PICKUP) {
                 if (task != curr)
                     break;
                 flags &= ~MUTEX_FLAG_PICKUP;
             } else if (handoff) {
                 if (flags & MUTEX_FLAG_HANDOFF)
                     break;
                 flags |= MUTEX_FLAG_HANDOFF;
             } else {
                 break;
             }
         } else {
             MUTEX_WARN_ON(flags & (MUTEX_FLAG_HANDOFF | MUTEX_FLAG_PICKUP));
             task = curr;
         }
 
         if (atomic_long_try_cmpxchg_acquire(&lock->owner, &owner, task | flags)) {
             if (task == curr)
                 return NULL;
             break;
         }
     }
 
     return __owner_task(owner);
 }
 
 /*
  * Trylock or set HANDOFF
  */
 static inline bool __mutex_trylock_or_handoff(struct mutex *lock, bool handoff)
 {
     return !__mutex_trylock_common(lock, handoff);
 }
 
 /*
  * Actual trylock that will work on any unlocked state.
  */
 static inline bool __mutex_trylock(struct mutex *lock)
 {
     return !__mutex_trylock_common(lock, false);
 }
 
 #ifndef CONFIG_DEBUG_LOCK_ALLOC
 /*
  * Lockdep annotations are contained to the slow paths for simplicity.
  * There is nothing that would stop spreading the lockdep annotations outwards
  * except more code.
  */
 
 /*
  * Optimistic trylock that only works in the uncontended case. Make sure to
  * follow with a __mutex_trylock() before failing.
  */
 static __always_inline bool __mutex_trylock_fast(struct mutex *lock)
 {
     unsigned long curr = (unsigned long)current;
     unsigned long zero = 0UL;
 
     if (atomic_long_try_cmpxchg_acquire(&lock->owner, &zero, curr))
         return true;
 
     return false;
 }
 
 static __always_inline bool __mutex_unlock_fast(struct mutex *lock)
 {
     unsigned long curr = (unsigned long)current;
 
     return atomic_long_try_cmpxchg_release(&lock->owner, &curr, 0UL);
 }
 #endif
 
 static inline void __mutex_set_flag(struct mutex *lock, unsigned long flag)
 {
     atomic_long_or(flag, &lock->owner);
 }
 
 static inline void __mutex_clear_flag(struct mutex *lock, unsigned long flag)
 {
     atomic_long_andnot(flag, &lock->owner);
 }
 
 static inline bool __mutex_waiter_is_first(struct mutex *lock, struct mutex_waiter *waiter)
 {
     return list_first_entry(&lock->wait_list, struct mutex_waiter, list) == waiter;
 }
 
 /*
  * Add @waiter to a given location in the lock wait_list and set the
  * FLAG_WAITERS flag if it's the first waiter.
  */
 static void
 __mutex_add_waiter(struct mutex *lock, struct mutex_waiter *waiter,
            struct list_head *list)
 {
     debug_mutex_add_waiter(lock, waiter, current);
 
     list_add_tail(&waiter->list, list);
     if (__mutex_waiter_is_first(lock, waiter))
         __mutex_set_flag(lock, MUTEX_FLAG_WAITERS);
 }
 
 static void
 __mutex_remove_waiter(struct mutex *lock, struct mutex_waiter *waiter)
 {
     list_del(&waiter->list);
     if (likely(list_empty(&lock->wait_list)))
         __mutex_clear_flag(lock, MUTEX_FLAGS);
 
     debug_mutex_remove_waiter(lock, waiter, current);
 }
 
 /*
  * Give up ownership to a specific task, when @task = NULL, this is equivalent
  * to a regular unlock. Sets PICKUP on a handoff, clears HANDOFF, preserves
  * WAITERS. Provides RELEASE semantics like a regular unlock, the
  * __mutex_trylock() provides a matching ACQUIRE semantics for the handoff.
  */
 static void __mutex_handoff(struct mutex *lock, struct task_struct *task)
 {
     unsigned long owner = atomic_long_read(&lock->owner);
 
     for (;;) {
         unsigned long new;
 
         MUTEX_WARN_ON(__owner_task(owner) != current);
         MUTEX_WARN_ON(owner & MUTEX_FLAG_PICKUP);
 
         new = (owner & MUTEX_FLAG_WAITERS);
         new |= (unsigned long)task;
         if (task)
             new |= MUTEX_FLAG_PICKUP;
 
         if (atomic_long_try_cmpxchg_release(&lock->owner, &owner, new))
             break;
     }
 }
 
 #ifndef CONFIG_DEBUG_LOCK_ALLOC
 /*
  * We split the mutex lock/unlock logic into separate fastpath and
  * slowpath functions, to reduce the register pressure on the fastpath.
  * We also put the fastpath first in the kernel image, to make sure the
  * branch is predicted by the CPU as default-untaken.
  */
 static void __sched __mutex_lock_slowpath(struct mutex *lock);
 
 /**
  * mutex_lock - acquire the mutex
  * @lock: the mutex to be acquired
  *
  * Lock the mutex exclusively for this task. If the mutex is not
  * available right now, it will sleep until it can get it.
  *
  * The mutex must later on be released by the same task that
  * acquired it. Recursive locking is not allowed. 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 CONFIG_DEBUG_MUTEXES .config option turns on debugging
  * checks that will enforce the restrictions and will also do
  * deadlock debugging)
  *
  * This function is similar to (but not equivalent to) down().
  */
 void __sched mutex_lock(struct mutex *lock)
 {
     might_sleep();
 
     if (!__mutex_trylock_fast(lock))
         __mutex_lock_slowpath(lock);
 }
 EXPORT_SYMBOL(mutex_lock);
 #endif
 
 #include "ww_mutex.h"
 
 #ifdef CONFIG_MUTEX_SPIN_ON_OWNER
 
 /*
  * Trylock variant that returns the owning task on failure.
  */
 static inline struct task_struct *__mutex_trylock_or_owner(struct mutex *lock)
 {
     return __mutex_trylock_common(lock, false);
 }
 
 static inline
 bool ww_mutex_spin_on_owner(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
                 struct mutex_waiter *waiter)
 {
     struct ww_mutex *ww;
 
     ww = container_of(lock, struct ww_mutex, base);
 
     /*
      * If ww->ctx is set the contents are undefined, only
      * by acquiring wait_lock there is a guarantee that
      * they are not invalid when reading.
      *
      * As such, when deadlock detection needs to be
      * performed the optimistic spinning cannot be done.
      *
      * Check this in every inner iteration because we may
      * be racing against another thread's ww_mutex_lock.
      */
     if (ww_ctx->acquired > 0 && READ_ONCE(ww->ctx))
         return false;
 
     /*
      * If we aren't on the wait list yet, cancel the spin
      * if there are waiters. We want  to avoid stealing the
      * lock from a waiter with an earlier stamp, since the
      * other thread may already own a lock that we also
      * need.
      */
     if (!waiter && (atomic_long_read(&lock->owner) & MUTEX_FLAG_WAITERS))
         return false;
 
     /*
      * Similarly, stop spinning if we are no longer the
      * first waiter.
      */
     if (waiter && !__mutex_waiter_is_first(lock, waiter))
         return false;
 
     return true;
 }
 
 /*
  * Look out! "owner" is an entirely speculative pointer access and not
  * reliable.
  *
  * "noinline" so that this function shows up on perf profiles.
  */
 static noinline
 bool mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner,
              struct ww_acquire_ctx *ww_ctx, struct mutex_waiter *waiter)
 {
     bool ret = true;
 
     lockdep_assert_preemption_disabled();
 
     while (__mutex_owner(lock) == owner) {
         /*
          * Ensure we emit the owner->on_cpu, dereference _after_
          * checking lock->owner still matches owner. And we already
          * disabled preemption which is equal to the RCU read-side
          * crital section in optimistic spinning code. Thus the
          * task_strcut structure won't go away during the spinning
          * period
          */
         barrier();
 
         /*
          * Use vcpu_is_preempted to detect lock holder preemption issue.
          */
         if (!owner_on_cpu(owner) || need_resched()) {
             ret = false;
             break;
         }
 
         if (ww_ctx && !ww_mutex_spin_on_owner(lock, ww_ctx, waiter)) {
             ret = false;
             break;
         }
 
         cpu_relax();
     }
 
     return ret;
 }
 
 /*
  * Initial check for entering the mutex spinning loop
  */
 static inline int mutex_can_spin_on_owner(struct mutex *lock)
 {
     struct task_struct *owner;
     int retval = 1;
 
     lockdep_assert_preemption_disabled();
 
     if (need_resched())
         return 0;
 
     /*
      * We already disabled preemption which is equal to the RCU read-side
      * crital section in optimistic spinning code. Thus the task_strcut
      * structure won't go away during the spinning period.
      */
     owner = __mutex_owner(lock);
     if (owner)
         retval = owner_on_cpu(owner);
 
     /*
      * If lock->owner is not set, the mutex has been released. Return true
      * such that we'll trylock in the spin path, which is a faster option
      * than the blocking slow path.
      */
     return retval;
 }
 
 /*
  * Optimistic spinning.
  *
  * We try to spin for acquisition when we find that the lock owner
  * is currently running on a (different) CPU and while we don't
  * need to reschedule. The rationale is that if the lock owner is
  * running, it is likely to release the lock soon.
  *
  * The mutex spinners are queued up using MCS lock so that only one
  * spinner can compete for the mutex. However, if mutex spinning isn't
  * going to happen, there is no point in going through the lock/unlock
  * overhead.
  *
  * Returns true when the lock was taken, otherwise false, indicating
  * that we need to jump to the slowpath and sleep.
  *
  * The waiter flag is set to true if the spinner is a waiter in the wait
  * queue. The waiter-spinner will spin on the lock directly and concurrently
  * with the spinner at the head of the OSQ, if present, until the owner is
  * changed to itself.
  */
 static __always_inline bool
 mutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
               struct mutex_waiter *waiter)
 {
     if (!waiter) {
         /*
          * The purpose of the mutex_can_spin_on_owner() function is
          * to eliminate the overhead of osq_lock() and osq_unlock()
          * in case spinning isn't possible. As a waiter-spinner
          * is not going to take OSQ lock anyway, there is no need
          * to call mutex_can_spin_on_owner().
          */
         if (!mutex_can_spin_on_owner(lock))
             goto fail;
 
         /*
          * In order to avoid a stampede of mutex spinners trying to
          * acquire the mutex all at once, the spinners need to take a
          * MCS (queued) lock first before spinning on the owner field.
          */
         if (!osq_lock(&lock->osq))
             goto fail;
     }
 
     for (;;) {
         struct task_struct *owner;
 
         /* Try to acquire the mutex... */
         owner = __mutex_trylock_or_owner(lock);
         if (!owner)
             break;
 
         /*
          * There's an owner, wait for it to either
          * release the lock or go to sleep.
          */
         if (!mutex_spin_on_owner(lock, owner, ww_ctx, waiter))
             goto fail_unlock;
 
         /*
          * The cpu_relax() call is a compiler barrier which forces
          * everything in this loop to be re-loaded. We don't need
          * memory barriers as we'll eventually observe the right
          * values at the cost of a few extra spins.
          */
         cpu_relax();
     }
 
     if (!waiter)
         osq_unlock(&lock->osq);
 
     return true;
 
 
 fail_unlock:
     if (!waiter)
         osq_unlock(&lock->osq);
 
 fail:
     /*
      * If we fell out of the spin path because of need_resched(),
      * reschedule now, before we try-lock the mutex. This avoids getting
      * scheduled out right after we obtained the mutex.
      */
     if (need_resched()) {
         /*
          * We _should_ have TASK_RUNNING here, but just in case
          * we do not, make it so, otherwise we might get stuck.
          */
         __set_current_state(TASK_RUNNING);
         schedule_preempt_disabled();
     }
 
     return false;
 }
 #else
 static __always_inline bool
 mutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
               struct mutex_waiter *waiter)
 {
     return false;
 }
 #endif
 
 static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip);
 
 /**
  * mutex_unlock - release the mutex
  * @lock: the mutex to be released
  *
  * Unlock a mutex that has been locked by this task previously.
  *
  * This function must not be used in interrupt context. Unlocking
  * of a not locked mutex is not allowed.
  *
  * This function is similar to (but not equivalent to) up().
  */
 void __sched mutex_unlock(struct mutex *lock)
 {
 #ifndef CONFIG_DEBUG_LOCK_ALLOC
     if (__mutex_unlock_fast(lock))
         return;
 #endif
     __mutex_unlock_slowpath(lock, _RET_IP_);
 }
 EXPORT_SYMBOL(mutex_unlock);
 
 /**
  * ww_mutex_unlock - release the w/w mutex
  * @lock: the mutex to be released
  *
  * Unlock a mutex that has been locked by this task previously with any of the
  * ww_mutex_lock* functions (with or without an acquire context). It is
  * forbidden to release the locks after releasing the acquire context.
  *
  * This function must not be used in interrupt context. Unlocking
  * of a unlocked mutex is not allowed.
  */
 void __sched ww_mutex_unlock(struct ww_mutex *lock)
 {
     __ww_mutex_unlock(lock);
     mutex_unlock(&lock->base);
 }
 EXPORT_SYMBOL(ww_mutex_unlock);
 
 /*
  * Lock a mutex (possibly interruptible), slowpath:
  */
 static __always_inline int __sched
 __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclass,
             struct lockdep_map *nest_lock, unsigned long ip,
             struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx)
 {
     struct mutex_waiter waiter;
     struct ww_mutex *ww;
     int ret;
 
     if (!use_ww_ctx)
         ww_ctx = NULL;
 
     might_sleep();
 
     MUTEX_WARN_ON(lock->magic != lock);
 
     ww = container_of(lock, struct ww_mutex, base);
     if (ww_ctx) {
         if (unlikely(ww_ctx == READ_ONCE(ww->ctx)))
             return -EALREADY;
 
         /*
          * Reset the wounded flag after a kill. No other process can
          * race and wound us here since they can't have a valid owner
          * pointer if we don't have any locks held.
          */
         if (ww_ctx->acquired == 0)
             ww_ctx->wounded = 0;
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
         nest_lock = &ww_ctx->dep_map;
 #endif
     }
 
     preempt_disable();
     mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip);
 
     trace_contention_begin(lock, LCB_F_MUTEX | LCB_F_SPIN);
     if (__mutex_trylock(lock) ||
         mutex_optimistic_spin(lock, ww_ctx, NULL)) {
         /* got the lock, yay! */
         lock_acquired(&lock->dep_map, ip);
         if (ww_ctx)
             ww_mutex_set_context_fastpath(ww, ww_ctx);
         trace_contention_end(lock, 0);
         preempt_enable();
         return 0;
     }
 
     raw_spin_lock(&lock->wait_lock);
     /*
      * After waiting to acquire the wait_lock, try again.
      */
     if (__mutex_trylock(lock)) {
         if (ww_ctx)
             __ww_mutex_check_waiters(lock, ww_ctx);
 
         goto skip_wait;
     }
 
     debug_mutex_lock_common(lock, &waiter);
     waiter.task = current;
     if (use_ww_ctx)
         waiter.ww_ctx = ww_ctx;
 
     lock_contended(&lock->dep_map, ip);
 
     if (!use_ww_ctx) {
         /* add waiting tasks to the end of the waitqueue (FIFO): */
         __mutex_add_waiter(lock, &waiter, &lock->wait_list);
     } else {
         /*
          * Add in stamp order, waking up waiters that must kill
          * themselves.
          */
         ret = __ww_mutex_add_waiter(&waiter, lock, ww_ctx);
         if (ret)
             goto err_early_kill;
     }
 
     set_current_state(state);
     trace_contention_begin(lock, LCB_F_MUTEX);
     for (;;) {
         bool first;
 
         /*
          * Once we hold wait_lock, we're serialized against
          * mutex_unlock() handing the lock off to us, do a trylock
          * before testing the error conditions to make sure we pick up
          * the handoff.
          */
         if (__mutex_trylock(lock))
             goto acquired;
 
         /*
          * Check for signals and kill conditions while holding
          * wait_lock. This ensures the lock cancellation is ordered
          * against mutex_unlock() and wake-ups do not go missing.
          */
         if (signal_pending_state(state, current)) {
             ret = -EINTR;
             goto err;
         }
 
         if (ww_ctx) {
             ret = __ww_mutex_check_kill(lock, &waiter, ww_ctx);
             if (ret)
                 goto err;
         }
 
         raw_spin_unlock(&lock->wait_lock);
         schedule_preempt_disabled();
 
         first = __mutex_waiter_is_first(lock, &waiter);
 
         set_current_state(state);
         /*
          * Here we order against unlock; we must either see it change
          * state back to RUNNING and fall through the next schedule(),
          * or we must see its unlock and acquire.
          */
         if (__mutex_trylock_or_handoff(lock, first))
             break;
 
         if (first) {
             trace_contention_begin(lock, LCB_F_MUTEX | LCB_F_SPIN);
             if (mutex_optimistic_spin(lock, ww_ctx, &waiter))
                 break;
             trace_contention_begin(lock, LCB_F_MUTEX);
         }
 
         raw_spin_lock(&lock->wait_lock);
     }
     raw_spin_lock(&lock->wait_lock);
 acquired:
     __set_current_state(TASK_RUNNING);
 
     if (ww_ctx) {
         /*
          * Wound-Wait; we stole the lock (!first_waiter), check the
          * waiters as anyone might want to wound us.
          */
         if (!ww_ctx->is_wait_die &&
             !__mutex_waiter_is_first(lock, &waiter))
             __ww_mutex_check_waiters(lock, ww_ctx);
     }
 
     __mutex_remove_waiter(lock, &waiter);
 
     debug_mutex_free_waiter(&waiter);
 
 skip_wait:
     /* got the lock - cleanup and rejoice! */
     lock_acquired(&lock->dep_map, ip);
     trace_contention_end(lock, 0);
 
     if (ww_ctx)
         ww_mutex_lock_acquired(ww, ww_ctx);
 
     raw_spin_unlock(&lock->wait_lock);
     preempt_enable();
     return 0;
 
 err:
     __set_current_state(TASK_RUNNING);
     __mutex_remove_waiter(lock, &waiter);
 err_early_kill:
     trace_contention_end(lock, ret);
     raw_spin_unlock(&lock->wait_lock);
     debug_mutex_free_waiter(&waiter);
     mutex_release(&lock->dep_map, ip);
     preempt_enable();
     return ret;
 }
 
 static int __sched
 __mutex_lock(struct mutex *lock, unsigned int state, unsigned int subclass,
          struct lockdep_map *nest_lock, unsigned long ip)
 {
     return __mutex_lock_common(lock, state, subclass, nest_lock, ip, NULL, false);
 }
 
 static int __sched
 __ww_mutex_lock(struct mutex *lock, unsigned int state, unsigned int subclass,
         unsigned long ip, struct ww_acquire_ctx *ww_ctx)
 {
     return __mutex_lock_common(lock, state, subclass, NULL, ip, ww_ctx, true);
 }
 
 /**
  * ww_mutex_trylock - tries to acquire the w/w mutex with optional acquire context
  * @ww: mutex to lock
  * @ww_ctx: optional w/w acquire context
  *
  * Trylocks a mutex with the optional acquire context; no deadlock detection is
  * possible. Returns 1 if the mutex has been acquired successfully, 0 otherwise.
  *
  * Unlike ww_mutex_lock, no deadlock handling is performed. However, if a @ctx is
  * specified, -EALREADY handling may happen in calls to ww_mutex_trylock.
  *
  * A mutex acquired with this function must be released with ww_mutex_unlock.
  */
 int ww_mutex_trylock(struct ww_mutex *ww, struct ww_acquire_ctx *ww_ctx)
 {
     if (!ww_ctx)
         return mutex_trylock(&ww->base);
 
     MUTEX_WARN_ON(ww->base.magic != &ww->base);
 
     /*
      * Reset the wounded flag after a kill. No other process can
      * race and wound us here, since they can't have a valid owner
      * pointer if we don't have any locks held.
      */
     if (ww_ctx->acquired == 0)
         ww_ctx->wounded = 0;
 
     if (__mutex_trylock(&ww->base)) {
         ww_mutex_set_context_fastpath(ww, ww_ctx);
         mutex_acquire_nest(&ww->base.dep_map, 0, 1, &ww_ctx->dep_map, _RET_IP_);
         return 1;
     }
 
     return 0;
 }
 EXPORT_SYMBOL(ww_mutex_trylock);
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 void __sched
 mutex_lock_nested(struct mutex *lock, unsigned int subclass)
 {
     __mutex_lock(lock, TASK_UNINTERRUPTIBLE, subclass, NULL, _RET_IP_);
 }
 
 EXPORT_SYMBOL_GPL(mutex_lock_nested);
 
 void __sched
 _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest)
 {
     __mutex_lock(lock, TASK_UNINTERRUPTIBLE, 0, nest, _RET_IP_);
 }
 EXPORT_SYMBOL_GPL(_mutex_lock_nest_lock);
 
 int __sched
 mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass)
 {
     return __mutex_lock(lock, TASK_KILLABLE, subclass, NULL, _RET_IP_);
 }
 EXPORT_SYMBOL_GPL(mutex_lock_killable_nested);
 
 int __sched
 mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass)
 {
     return __mutex_lock(lock, TASK_INTERRUPTIBLE, subclass, NULL, _RET_IP_);
 }
 EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested);
 
 void __sched
 mutex_lock_io_nested(struct mutex *lock, unsigned int subclass)
 {
     int token;
 
     might_sleep();
 
     token = io_schedule_prepare();
     __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE,
                 subclass, NULL, _RET_IP_, NULL, 0);
     io_schedule_finish(token);
 }
 EXPORT_SYMBOL_GPL(mutex_lock_io_nested);
 
 static inline int
 ww_mutex_deadlock_injection(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 {
 #ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
     unsigned tmp;
 
     if (ctx->deadlock_inject_countdown-- == 0) {
         tmp = ctx->deadlock_inject_interval;
         if (tmp > UINT_MAX/4)
             tmp = UINT_MAX;
         else
             tmp = tmp*2 + tmp + tmp/2;
 
         ctx->deadlock_inject_interval = tmp;
         ctx->deadlock_inject_countdown = tmp;
         ctx->contending_lock = lock;
 
         ww_mutex_unlock(lock);
 
         return -EDEADLK;
     }
 #endif
 
     return 0;
 }
 
 int __sched
 ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 {
     int ret;
 
     might_sleep();
     ret =  __ww_mutex_lock(&lock->base, TASK_UNINTERRUPTIBLE,
                    0, _RET_IP_, ctx);
     if (!ret && ctx && ctx->acquired > 1)
         return ww_mutex_deadlock_injection(lock, ctx);
 
     return ret;
 }
 EXPORT_SYMBOL_GPL(ww_mutex_lock);
 
 int __sched
 ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 {
     int ret;
 
     might_sleep();
     ret = __ww_mutex_lock(&lock->base, TASK_INTERRUPTIBLE,
                   0, _RET_IP_, ctx);
 
     if (!ret && ctx && ctx->acquired > 1)
         return ww_mutex_deadlock_injection(lock, ctx);
 
     return ret;
 }
 EXPORT_SYMBOL_GPL(ww_mutex_lock_interruptible);
 
 #endif
 
 /*
  * Release the lock, slowpath:
  */
 static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip)
 {
     struct task_struct *next = NULL;
     DEFINE_WAKE_Q(wake_q);
     unsigned long owner;
 
     mutex_release(&lock->dep_map, ip);
 
     /*
      * Release the lock before (potentially) taking the spinlock such that
      * other contenders can get on with things ASAP.
      *
      * Except when HANDOFF, in that case we must not clear the owner field,
      * but instead set it to the top waiter.
      */
     owner = atomic_long_read(&lock->owner);
     for (;;) {
         MUTEX_WARN_ON(__owner_task(owner) != current);
         MUTEX_WARN_ON(owner & MUTEX_FLAG_PICKUP);
 
         if (owner & MUTEX_FLAG_HANDOFF)
             break;
 
         if (atomic_long_try_cmpxchg_release(&lock->owner, &owner, __owner_flags(owner))) {
             if (owner & MUTEX_FLAG_WAITERS)
                 break;
 
             return;
         }
     }
 
     raw_spin_lock(&lock->wait_lock);
     debug_mutex_unlock(lock);
     if (!list_empty(&lock->wait_list)) {
         /* get the first entry from the wait-list: */
         struct mutex_waiter *waiter =
             list_first_entry(&lock->wait_list,
                      struct mutex_waiter, list);
 
         next = waiter->task;
 
         debug_mutex_wake_waiter(lock, waiter);
         wake_q_add(&wake_q, next);
     }
 
     if (owner & MUTEX_FLAG_HANDOFF)
         __mutex_handoff(lock, next);
 
     raw_spin_unlock(&lock->wait_lock);
 
     wake_up_q(&wake_q);
 }
 
 #ifndef CONFIG_DEBUG_LOCK_ALLOC
 /*
  * Here come the less common (and hence less performance-critical) APIs:
  * mutex_lock_interruptible() and mutex_trylock().
  */
 static noinline int __sched
 __mutex_lock_killable_slowpath(struct mutex *lock);
 
 static noinline int __sched
 __mutex_lock_interruptible_slowpath(struct mutex *lock);
 
 /**
  * mutex_lock_interruptible() - Acquire the mutex, interruptible by signals.
  * @lock: The mutex to be acquired.
  *
  * Lock the mutex like mutex_lock().  If a signal is delivered while the
  * process is sleeping, this function will return without acquiring the
  * mutex.
  *
  * Context: Process context.
  * Return: 0 if the lock was successfully acquired or %-EINTR if a
  * signal arrived.
  */
 int __sched mutex_lock_interruptible(struct mutex *lock)
 {
     might_sleep();
 
     if (__mutex_trylock_fast(lock))
         return 0;
 
     return __mutex_lock_interruptible_slowpath(lock);
 }
 
 EXPORT_SYMBOL(mutex_lock_interruptible);
 
 /**
  * mutex_lock_killable() - Acquire the mutex, interruptible by fatal signals.
  * @lock: The mutex to be acquired.
  *
  * Lock the mutex like mutex_lock().  If a signal which will be fatal to
  * the current process is delivered while the process is sleeping, this
  * function will return without acquiring the mutex.
  *
  * Context: Process context.
  * Return: 0 if the lock was successfully acquired or %-EINTR if a
  * fatal signal arrived.
  */
 int __sched mutex_lock_killable(struct mutex *lock)
 {
     might_sleep();
 
     if (__mutex_trylock_fast(lock))
         return 0;
 
     return __mutex_lock_killable_slowpath(lock);
 }
 EXPORT_SYMBOL(mutex_lock_killable);
 
 /**
  * mutex_lock_io() - Acquire the mutex and mark the process as waiting for I/O
  * @lock: The mutex to be acquired.
  *
  * Lock the mutex like mutex_lock().  While the task is waiting for this
  * mutex, it will be accounted as being in the IO wait state by the
  * scheduler.
  *
  * Context: Process context.
  */
 void __sched mutex_lock_io(struct mutex *lock)
 {
     int token;
 
     token = io_schedule_prepare();
     mutex_lock(lock);
     io_schedule_finish(token);
 }
 EXPORT_SYMBOL_GPL(mutex_lock_io);
 
 static noinline void __sched
 __mutex_lock_slowpath(struct mutex *lock)
 {
     __mutex_lock(lock, TASK_UNINTERRUPTIBLE, 0, NULL, _RET_IP_);
 }
 
 static noinline int __sched
 __mutex_lock_killable_slowpath(struct mutex *lock)
 {
     return __mutex_lock(lock, TASK_KILLABLE, 0, NULL, _RET_IP_);
 }
 
 static noinline int __sched
 __mutex_lock_interruptible_slowpath(struct mutex *lock)
 {
     return __mutex_lock(lock, TASK_INTERRUPTIBLE, 0, NULL, _RET_IP_);
 }
 
 static noinline int __sched
 __ww_mutex_lock_slowpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 {
     return __ww_mutex_lock(&lock->base, TASK_UNINTERRUPTIBLE, 0,
                    _RET_IP_, ctx);
 }
 
 static noinline int __sched
 __ww_mutex_lock_interruptible_slowpath(struct ww_mutex *lock,
                         struct ww_acquire_ctx *ctx)
 {
     return __ww_mutex_lock(&lock->base, TASK_INTERRUPTIBLE, 0,
                    _RET_IP_, ctx);
 }
 
 #endif
 
 /**
  * mutex_trylock - try to acquire the mutex, without waiting
  * @lock: the mutex to be acquired
  *
  * Try to acquire the mutex atomically. Returns 1 if the mutex
  * has been acquired successfully, and 0 on contention.
  *
  * NOTE: this function follows the spin_trylock() convention, so
  * it is negated from the down_trylock() return values! Be careful
  * about this when converting semaphore users to mutexes.
  *
  * This function must not be used in interrupt context. The
  * mutex must be released by the same task that acquired it.
  */
 int __sched mutex_trylock(struct mutex *lock)
 {
     bool locked;
 
     MUTEX_WARN_ON(lock->magic != lock);
 
     locked = __mutex_trylock(lock);
     if (locked)
         mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
 
     return locked;
 }
 EXPORT_SYMBOL(mutex_trylock);
 
 #ifndef CONFIG_DEBUG_LOCK_ALLOC
 int __sched
 ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 {
     might_sleep();
 
     if (__mutex_trylock_fast(&lock->base)) {
         if (ctx)
             ww_mutex_set_context_fastpath(lock, ctx);
         return 0;
     }
 
     return __ww_mutex_lock_slowpath(lock, ctx);
 }
 EXPORT_SYMBOL(ww_mutex_lock);
 
 int __sched
 ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 {
     might_sleep();
 
     if (__mutex_trylock_fast(&lock->base)) {
         if (ctx)
             ww_mutex_set_context_fastpath(lock, ctx);
         return 0;
     }
 
     return __ww_mutex_lock_interruptible_slowpath(lock, ctx);
 }
 EXPORT_SYMBOL(ww_mutex_lock_interruptible);
 
 #endif /* !CONFIG_DEBUG_LOCK_ALLOC */
 #endif /* !CONFIG_PREEMPT_RT */
 
 /**
  * atomic_dec_and_mutex_lock - return holding mutex if we dec to 0
  * @cnt: the atomic which we are to dec
  * @lock: the mutex to return holding if we dec to 0
  *
  * return true and hold lock if we dec to 0, return false otherwise
  */
 int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock)
 {
     /* dec if we can't possibly hit 0 */
     if (atomic_add_unless(cnt, -1, 1))
         return 0;
     /* we might hit 0, so take the lock */
     mutex_lock(lock);
     if (!atomic_dec_and_test(cnt)) {
         /* when we actually did the dec, we didn't hit 0 */
         mutex_unlock(lock);
         return 0;
     }
     /* we hit 0, and we hold the lock */
     return 1;
 }
 EXPORT_SYMBOL(atomic_dec_and_mutex_lock);

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