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 // SPDX-License-Identifier: GPL-2.0-only
 /*
  * RT-Mutexes: simple blocking mutual exclusion locks with PI support
  *
  * started by Ingo Molnar and Thomas Gleixner.
  *
  *  Copyright (C) 2004-2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
  *  Copyright (C) 2005-2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
  *  Copyright (C) 2005 Kihon Technologies Inc., Steven Rostedt
  *  Copyright (C) 2006 Esben Nielsen
  * Adaptive Spinlocks:
  *  Copyright (C) 2008 Novell, Inc., Gregory Haskins, Sven Dietrich,
  *                   and Peter Morreale,
  * Adaptive Spinlocks simplification:
  *  Copyright (C) 2008 Red Hat, Inc., Steven Rostedt <srostedt@redhat.com>
  *
  *  See Documentation/locking/rt-mutex-design.rst for details.
  */
 #include <linux/sched.h>
 #include <linux/sched/debug.h>
 #include <linux/sched/deadline.h>
 #include <linux/sched/signal.h>
 #include <linux/sched/rt.h>
 #include <linux/sched/wake_q.h>
 #include <linux/ww_mutex.h>
 
 #include <trace/events/lock.h>
 
 #include "rtmutex_common.h"
 
 #ifndef WW_RT
 # define build_ww_mutex()   (false)
 # define ww_container_of(rtm)   NULL
 
 static inline int __ww_mutex_add_waiter(struct rt_mutex_waiter *waiter,
                     struct rt_mutex *lock,
                     struct ww_acquire_ctx *ww_ctx)
 {
     return 0;
 }
 
 static inline void __ww_mutex_check_waiters(struct rt_mutex *lock,
                         struct ww_acquire_ctx *ww_ctx)
 {
 }
 
 static inline void ww_mutex_lock_acquired(struct ww_mutex *lock,
                       struct ww_acquire_ctx *ww_ctx)
 {
 }
 
 static inline int __ww_mutex_check_kill(struct rt_mutex *lock,
                     struct rt_mutex_waiter *waiter,
                     struct ww_acquire_ctx *ww_ctx)
 {
     return 0;
 }
 
 #else
 # define build_ww_mutex()   (true)
 # define ww_container_of(rtm)   container_of(rtm, struct ww_mutex, base)
 # include "ww_mutex.h"
 #endif
 
 /*
  * lock->owner state tracking:
  *
  * lock->owner holds the task_struct pointer of the owner. Bit 0
  * is used to keep track of the "lock has waiters" state.
  *
  * owner    bit0
  * NULL     0   lock is free (fast acquire possible)
  * NULL     1   lock is free and has waiters and the top waiter
  *              is going to take the lock*
  * taskpointer  0   lock is held (fast release possible)
  * taskpointer  1   lock is held and has waiters**
  *
  * The fast atomic compare exchange based acquire and release is only
  * possible when bit 0 of lock->owner is 0.
  *
  * (*) It also can be a transitional state when grabbing the lock
  * with ->wait_lock is held. To prevent any fast path cmpxchg to the lock,
  * we need to set the bit0 before looking at the lock, and the owner may be
  * NULL in this small time, hence this can be a transitional state.
  *
  * (**) There is a small time when bit 0 is set but there are no
  * waiters. This can happen when grabbing the lock in the slow path.
  * To prevent a cmpxchg of the owner releasing the lock, we need to
  * set this bit before looking at the lock.
  */
 
 static __always_inline void
 rt_mutex_set_owner(struct rt_mutex_base *lock, struct task_struct *owner)
 {
     unsigned long val = (unsigned long)owner;
 
     if (rt_mutex_has_waiters(lock))
         val |= RT_MUTEX_HAS_WAITERS;
 
     WRITE_ONCE(lock->owner, (struct task_struct *)val);
 }
 
 static __always_inline void clear_rt_mutex_waiters(struct rt_mutex_base *lock)
 {
     lock->owner = (struct task_struct *)
             ((unsigned long)lock->owner & ~RT_MUTEX_HAS_WAITERS);
 }
 
 static __always_inline void fixup_rt_mutex_waiters(struct rt_mutex_base *lock)
 {
     unsigned long owner, *p = (unsigned long *) &lock->owner;
 
     if (rt_mutex_has_waiters(lock))
         return;
 
     /*
      * The rbtree has no waiters enqueued, now make sure that the
      * lock->owner still has the waiters bit set, otherwise the
      * following can happen:
      *
      * CPU 0    CPU 1       CPU2
      * l->owner=T1
      *      rt_mutex_lock(l)
      *      lock(l->lock)
      *      l->owner = T1 | HAS_WAITERS;
      *      enqueue(T2)
      *      boost()
      *        unlock(l->lock)
      *      block()
      *
      *              rt_mutex_lock(l)
      *              lock(l->lock)
      *              l->owner = T1 | HAS_WAITERS;
      *              enqueue(T3)
      *              boost()
      *                unlock(l->lock)
      *              block()
      *      signal(->T2)    signal(->T3)
      *      lock(l->lock)
      *      dequeue(T2)
      *      deboost()
      *        unlock(l->lock)
      *              lock(l->lock)
      *              dequeue(T3)
      *               ==> wait list is empty
      *              deboost()
      *               unlock(l->lock)
      *      lock(l->lock)
      *      fixup_rt_mutex_waiters()
      *        if (wait_list_empty(l) {
      *          l->owner = owner
      *          owner = l->owner & ~HAS_WAITERS;
      *            ==> l->owner = T1
      *        }
      *              lock(l->lock)
      * rt_mutex_unlock(l)       fixup_rt_mutex_waiters()
      *                if (wait_list_empty(l) {
      *                  owner = l->owner & ~HAS_WAITERS;
      * cmpxchg(l->owner, T1, NULL)
      *  ===> Success (l->owner = NULL)
      *
      *                  l->owner = owner
      *                    ==> l->owner = T1
      *                }
      *
      * With the check for the waiter bit in place T3 on CPU2 will not
      * overwrite. All tasks fiddling with the waiters bit are
      * serialized by l->lock, so nothing else can modify the waiters
      * bit. If the bit is set then nothing can change l->owner either
      * so the simple RMW is safe. The cmpxchg() will simply fail if it
      * happens in the middle of the RMW because the waiters bit is
      * still set.
      */
     owner = READ_ONCE(*p);
     if (owner & RT_MUTEX_HAS_WAITERS)
         WRITE_ONCE(*p, owner & ~RT_MUTEX_HAS_WAITERS);
 }
 
 /*
  * We can speed up the acquire/release, if there's no debugging state to be
  * set up.
  */
 #ifndef CONFIG_DEBUG_RT_MUTEXES
 static __always_inline bool rt_mutex_cmpxchg_acquire(struct rt_mutex_base *lock,
                              struct task_struct *old,
                              struct task_struct *new)
 {
     return try_cmpxchg_acquire(&lock->owner, &old, new);
 }
 
 static __always_inline bool rt_mutex_cmpxchg_release(struct rt_mutex_base *lock,
                              struct task_struct *old,
                              struct task_struct *new)
 {
     return try_cmpxchg_release(&lock->owner, &old, new);
 }
 
 /*
  * Callers must hold the ->wait_lock -- which is the whole purpose as we force
  * all future threads that attempt to [Rmw] the lock to the slowpath. As such
  * relaxed semantics suffice.
  */
 static __always_inline void mark_rt_mutex_waiters(struct rt_mutex_base *lock)
 {
     unsigned long owner, *p = (unsigned long *) &lock->owner;
 
     do {
         owner = *p;
     } while (cmpxchg_relaxed(p, owner,
                  owner | RT_MUTEX_HAS_WAITERS) != owner);
 }
 
 /*
  * Safe fastpath aware unlock:
  * 1) Clear the waiters bit
  * 2) Drop lock->wait_lock
  * 3) Try to unlock the lock with cmpxchg
  */
 static __always_inline bool unlock_rt_mutex_safe(struct rt_mutex_base *lock,
                          unsigned long flags)
     __releases(lock->wait_lock)
 {
     struct task_struct *owner = rt_mutex_owner(lock);
 
     clear_rt_mutex_waiters(lock);
     raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
     /*
      * If a new waiter comes in between the unlock and the cmpxchg
      * we have two situations:
      *
      * unlock(wait_lock);
      *                  lock(wait_lock);
      * cmpxchg(p, owner, 0) == owner
      *                  mark_rt_mutex_waiters(lock);
      *                  acquire(lock);
      * or:
      *
      * unlock(wait_lock);
      *                  lock(wait_lock);
      *                  mark_rt_mutex_waiters(lock);
      *
      * cmpxchg(p, owner, 0) != owner
      *                  enqueue_waiter();
      *                  unlock(wait_lock);
      * lock(wait_lock);
      * wake waiter();
      * unlock(wait_lock);
      *                  lock(wait_lock);
      *                  acquire(lock);
      */
     return rt_mutex_cmpxchg_release(lock, owner, NULL);
 }
 
 #else
 static __always_inline bool rt_mutex_cmpxchg_acquire(struct rt_mutex_base *lock,
                              struct task_struct *old,
                              struct task_struct *new)
 {
     return false;
 
 }
 
 static __always_inline bool rt_mutex_cmpxchg_release(struct rt_mutex_base *lock,
                              struct task_struct *old,
                              struct task_struct *new)
 {
     return false;
 }
 
 static __always_inline void mark_rt_mutex_waiters(struct rt_mutex_base *lock)
 {
     lock->owner = (struct task_struct *)
             ((unsigned long)lock->owner | RT_MUTEX_HAS_WAITERS);
 }
 
 /*
  * Simple slow path only version: lock->owner is protected by lock->wait_lock.
  */
 static __always_inline bool unlock_rt_mutex_safe(struct rt_mutex_base *lock,
                          unsigned long flags)
     __releases(lock->wait_lock)
 {
     lock->owner = NULL;
     raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
     return true;
 }
 #endif
 
 static __always_inline int __waiter_prio(struct task_struct *task)
 {
     int prio = task->prio;
 
     if (!rt_prio(prio))
         return DEFAULT_PRIO;
 
     return prio;
 }
 
 static __always_inline void
 waiter_update_prio(struct rt_mutex_waiter *waiter, struct task_struct *task)
 {
     waiter->prio = __waiter_prio(task);
     waiter->deadline = task->dl.deadline;
 }
 
 /*
  * Only use with rt_mutex_waiter_{less,equal}()
  */
 #define task_to_waiter(p)   \
     &(struct rt_mutex_waiter){ .prio = __waiter_prio(p), .deadline = (p)->dl.deadline }
 
 static __always_inline int rt_mutex_waiter_less(struct rt_mutex_waiter *left,
                         struct rt_mutex_waiter *right)
 {
     if (left->prio < right->prio)
         return 1;
 
     /*
      * If both waiters have dl_prio(), we check the deadlines of the
      * associated tasks.
      * If left waiter has a dl_prio(), and we didn't return 1 above,
      * then right waiter has a dl_prio() too.
      */
     if (dl_prio(left->prio))
         return dl_time_before(left->deadline, right->deadline);
 
     return 0;
 }
 
 static __always_inline int rt_mutex_waiter_equal(struct rt_mutex_waiter *left,
                          struct rt_mutex_waiter *right)
 {
     if (left->prio != right->prio)
         return 0;
 
     /*
      * If both waiters have dl_prio(), we check the deadlines of the
      * associated tasks.
      * If left waiter has a dl_prio(), and we didn't return 0 above,
      * then right waiter has a dl_prio() too.
      */
     if (dl_prio(left->prio))
         return left->deadline == right->deadline;
 
     return 1;
 }
 
 static inline bool rt_mutex_steal(struct rt_mutex_waiter *waiter,
                   struct rt_mutex_waiter *top_waiter)
 {
     if (rt_mutex_waiter_less(waiter, top_waiter))
         return true;
 
 #ifdef RT_MUTEX_BUILD_SPINLOCKS
     /*
      * Note that RT tasks are excluded from same priority (lateral)
      * steals to prevent the introduction of an unbounded latency.
      */
     if (rt_prio(waiter->prio) || dl_prio(waiter->prio))
         return false;
 
     return rt_mutex_waiter_equal(waiter, top_waiter);
 #else
     return false;
 #endif
 }
 
 #define __node_2_waiter(node) \
     rb_entry((node), struct rt_mutex_waiter, tree_entry)
 
 static __always_inline bool __waiter_less(struct rb_node *a, const struct rb_node *b)
 {
     struct rt_mutex_waiter *aw = __node_2_waiter(a);
     struct rt_mutex_waiter *bw = __node_2_waiter(b);
 
     if (rt_mutex_waiter_less(aw, bw))
         return 1;
 
     if (!build_ww_mutex())
         return 0;
 
     if (rt_mutex_waiter_less(bw, aw))
         return 0;
 
     /* NOTE: relies on waiter->ww_ctx being set before insertion */
     if (aw->ww_ctx) {
         if (!bw->ww_ctx)
             return 1;
 
         return (signed long)(aw->ww_ctx->stamp -
                      bw->ww_ctx->stamp) < 0;
     }
 
     return 0;
 }
 
 static __always_inline void
 rt_mutex_enqueue(struct rt_mutex_base *lock, struct rt_mutex_waiter *waiter)
 {
     rb_add_cached(&waiter->tree_entry, &lock->waiters, __waiter_less);
 }
 
 static __always_inline void
 rt_mutex_dequeue(struct rt_mutex_base *lock, struct rt_mutex_waiter *waiter)
 {
     if (RB_EMPTY_NODE(&waiter->tree_entry))
         return;
 
     rb_erase_cached(&waiter->tree_entry, &lock->waiters);
     RB_CLEAR_NODE(&waiter->tree_entry);
 }
 
 #define __node_2_pi_waiter(node) \
     rb_entry((node), struct rt_mutex_waiter, pi_tree_entry)
 
 static __always_inline bool
 __pi_waiter_less(struct rb_node *a, const struct rb_node *b)
 {
     return rt_mutex_waiter_less(__node_2_pi_waiter(a), __node_2_pi_waiter(b));
 }
 
 static __always_inline void
 rt_mutex_enqueue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
 {
     rb_add_cached(&waiter->pi_tree_entry, &task->pi_waiters, __pi_waiter_less);
 }
 
 static __always_inline void
 rt_mutex_dequeue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
 {
     if (RB_EMPTY_NODE(&waiter->pi_tree_entry))
         return;
 
     rb_erase_cached(&waiter->pi_tree_entry, &task->pi_waiters);
     RB_CLEAR_NODE(&waiter->pi_tree_entry);
 }
 
 static __always_inline void rt_mutex_adjust_prio(struct task_struct *p)
 {
     struct task_struct *pi_task = NULL;
 
     lockdep_assert_held(&p->pi_lock);
 
     if (task_has_pi_waiters(p))
         pi_task = task_top_pi_waiter(p)->task;
 
     rt_mutex_setprio(p, pi_task);
 }
 
 /* RT mutex specific wake_q wrappers */
 static __always_inline void rt_mutex_wake_q_add_task(struct rt_wake_q_head *wqh,
                              struct task_struct *task,
                              unsigned int wake_state)
 {
     if (IS_ENABLED(CONFIG_PREEMPT_RT) && wake_state == TASK_RTLOCK_WAIT) {
         if (IS_ENABLED(CONFIG_PROVE_LOCKING))
             WARN_ON_ONCE(wqh->rtlock_task);
         get_task_struct(task);
         wqh->rtlock_task = task;
     } else {
         wake_q_add(&wqh->head, task);
     }
 }
 
 static __always_inline void rt_mutex_wake_q_add(struct rt_wake_q_head *wqh,
                         struct rt_mutex_waiter *w)
 {
     rt_mutex_wake_q_add_task(wqh, w->task, w->wake_state);
 }
 
 static __always_inline void rt_mutex_wake_up_q(struct rt_wake_q_head *wqh)
 {
     if (IS_ENABLED(CONFIG_PREEMPT_RT) && wqh->rtlock_task) {
         wake_up_state(wqh->rtlock_task, TASK_RTLOCK_WAIT);
         put_task_struct(wqh->rtlock_task);
         wqh->rtlock_task = NULL;
     }
 
     if (!wake_q_empty(&wqh->head))
         wake_up_q(&wqh->head);
 
     /* Pairs with preempt_disable() in mark_wakeup_next_waiter() */
     preempt_enable();
 }
 
 /*
  * Deadlock detection is conditional:
  *
  * If CONFIG_DEBUG_RT_MUTEXES=n, deadlock detection is only conducted
  * if the detect argument is == RT_MUTEX_FULL_CHAINWALK.
  *
  * If CONFIG_DEBUG_RT_MUTEXES=y, deadlock detection is always
  * conducted independent of the detect argument.
  *
  * If the waiter argument is NULL this indicates the deboost path and
  * deadlock detection is disabled independent of the detect argument
  * and the config settings.
  */
 static __always_inline bool
 rt_mutex_cond_detect_deadlock(struct rt_mutex_waiter *waiter,
                   enum rtmutex_chainwalk chwalk)
 {
     if (IS_ENABLED(CONFIG_DEBUG_RT_MUTEXES))
         return waiter != NULL;
     return chwalk == RT_MUTEX_FULL_CHAINWALK;
 }
 
 static __always_inline struct rt_mutex_base *task_blocked_on_lock(struct task_struct *p)
 {
     return p->pi_blocked_on ? p->pi_blocked_on->lock : NULL;
 }
 
 /*
  * Adjust the priority chain. Also used for deadlock detection.
  * Decreases task's usage by one - may thus free the task.
  *
  * @task:   the task owning the mutex (owner) for which a chain walk is
  *      probably needed
  * @chwalk: do we have to carry out deadlock detection?
  * @orig_lock:  the mutex (can be NULL if we are walking the chain to recheck
  *      things for a task that has just got its priority adjusted, and
  *      is waiting on a mutex)
  * @next_lock:  the mutex on which the owner of @orig_lock was blocked before
  *      we dropped its pi_lock. Is never dereferenced, only used for
  *      comparison to detect lock chain changes.
  * @orig_waiter: rt_mutex_waiter struct for the task that has just donated
  *      its priority to the mutex owner (can be NULL in the case
  *      depicted above or if the top waiter is gone away and we are
  *      actually deboosting the owner)
  * @top_task:   the current top waiter
  *
  * Returns 0 or -EDEADLK.
  *
  * Chain walk basics and protection scope
  *
  * [R] refcount on task
  * [P] task->pi_lock held
  * [L] rtmutex->wait_lock held
  *
  * Step Description             Protected by
  *  function arguments:
  *  @task                   [R]
  *  @orig_lock if != NULL           @top_task is blocked on it
  *  @next_lock              Unprotected. Cannot be
  *                      dereferenced. Only used for
  *                      comparison.
  *  @orig_waiter if != NULL         @top_task is blocked on it
  *  @top_task               current, or in case of proxy
  *                      locking protected by calling
  *                      code
  *  again:
  *    loop_sanity_check();
  *  retry:
  * [1]    lock(task->pi_lock);          [R] acquire [P]
  * [2]    waiter = task->pi_blocked_on;     [P]
  * [3]    check_exit_conditions_1();        [P]
  * [4]    lock = waiter->lock;          [P]
  * [5]    if (!try_lock(lock->wait_lock)) { [P] try to acquire [L]
  *      unlock(task->pi_lock);      release [P]
  *      goto retry;
  *    }
  * [6]    check_exit_conditions_2();        [P] + [L]
  * [7]    requeue_lock_waiter(lock, waiter);    [P] + [L]
  * [8]    unlock(task->pi_lock);        release [P]
  *    put_task_struct(task);        release [R]
  * [9]    check_exit_conditions_3();        [L]
  * [10]   task = owner(lock);           [L]
  *    get_task_struct(task);        [L] acquire [R]
  *    lock(task->pi_lock);          [L] acquire [P]
  * [11]   requeue_pi_waiter(tsk, waiters(lock));[P] + [L]
  * [12]   check_exit_conditions_4();        [P] + [L]
  * [13]   unlock(task->pi_lock);        release [P]
  *    unlock(lock->wait_lock);      release [L]
  *    goto again;
  */
 static int __sched rt_mutex_adjust_prio_chain(struct task_struct *task,
                           enum rtmutex_chainwalk chwalk,
                           struct rt_mutex_base *orig_lock,
                           struct rt_mutex_base *next_lock,
                           struct rt_mutex_waiter *orig_waiter,
                           struct task_struct *top_task)
 {
     struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;
     struct rt_mutex_waiter *prerequeue_top_waiter;
     int ret = 0, depth = 0;
     struct rt_mutex_base *lock;
     bool detect_deadlock;
     bool requeue = true;
 
     detect_deadlock = rt_mutex_cond_detect_deadlock(orig_waiter, chwalk);
 
     /*
      * The (de)boosting is a step by step approach with a lot of
      * pitfalls. We want this to be preemptible and we want hold a
      * maximum of two locks per step. So we have to check
      * carefully whether things change under us.
      */
  again:
     /*
      * We limit the lock chain length for each invocation.
      */
     if (++depth > max_lock_depth) {
         static int prev_max;
 
         /*
          * Print this only once. If the admin changes the limit,
          * print a new message when reaching the limit again.
          */
         if (prev_max != max_lock_depth) {
             prev_max = max_lock_depth;
             printk(KERN_WARNING "Maximum lock depth %d reached "
                    "task: %s (%d)\n", max_lock_depth,
                    top_task->comm, task_pid_nr(top_task));
         }
         put_task_struct(task);
 
         return -EDEADLK;
     }
 
     /*
      * We are fully preemptible here and only hold the refcount on
      * @task. So everything can have changed under us since the
      * caller or our own code below (goto retry/again) dropped all
      * locks.
      */
  retry:
     /*
      * [1] Task cannot go away as we did a get_task() before !
      */
     raw_spin_lock_irq(&task->pi_lock);
 
     /*
      * [2] Get the waiter on which @task is blocked on.
      */
     waiter = task->pi_blocked_on;
 
     /*
      * [3] check_exit_conditions_1() protected by task->pi_lock.
      */
 
     /*
      * Check whether the end of the boosting chain has been
      * reached or the state of the chain has changed while we
      * dropped the locks.
      */
     if (!waiter)
         goto out_unlock_pi;
 
     /*
      * Check the orig_waiter state. After we dropped the locks,
      * the previous owner of the lock might have released the lock.
      */
     if (orig_waiter && !rt_mutex_owner(orig_lock))
         goto out_unlock_pi;
 
     /*
      * We dropped all locks after taking a refcount on @task, so
      * the task might have moved on in the lock chain or even left
      * the chain completely and blocks now on an unrelated lock or
      * on @orig_lock.
      *
      * We stored the lock on which @task was blocked in @next_lock,
      * so we can detect the chain change.
      */
     if (next_lock != waiter->lock)
         goto out_unlock_pi;
 
     /*
      * There could be 'spurious' loops in the lock graph due to ww_mutex,
      * consider:
      *
      *   P1: A, ww_A, ww_B
      *   P2: ww_B, ww_A
      *   P3: A
      *
      * P3 should not return -EDEADLK because it gets trapped in the cycle
      * created by P1 and P2 (which will resolve -- and runs into
      * max_lock_depth above). Therefore disable detect_deadlock such that
      * the below termination condition can trigger once all relevant tasks
      * are boosted.
      *
      * Even when we start with ww_mutex we can disable deadlock detection,
      * since we would supress a ww_mutex induced deadlock at [6] anyway.
      * Supressing it here however is not sufficient since we might still
      * hit [6] due to adjustment driven iteration.
      *
      * NOTE: if someone were to create a deadlock between 2 ww_classes we'd
      * utterly fail to report it; lockdep should.
      */
     if (IS_ENABLED(CONFIG_PREEMPT_RT) && waiter->ww_ctx && detect_deadlock)
         detect_deadlock = false;
 
     /*
      * Drop out, when the task has no waiters. Note,
      * top_waiter can be NULL, when we are in the deboosting
      * mode!
      */
     if (top_waiter) {
         if (!task_has_pi_waiters(task))
             goto out_unlock_pi;
         /*
          * If deadlock detection is off, we stop here if we
          * are not the top pi waiter of the task. If deadlock
          * detection is enabled we continue, but stop the
          * requeueing in the chain walk.
          */
         if (top_waiter != task_top_pi_waiter(task)) {
             if (!detect_deadlock)
                 goto out_unlock_pi;
             else
                 requeue = false;
         }
     }
 
     /*
      * If the waiter priority is the same as the task priority
      * then there is no further priority adjustment necessary.  If
      * deadlock detection is off, we stop the chain walk. If its
      * enabled we continue, but stop the requeueing in the chain
      * walk.
      */
     if (rt_mutex_waiter_equal(waiter, task_to_waiter(task))) {
         if (!detect_deadlock)
             goto out_unlock_pi;
         else
             requeue = false;
     }
 
     /*
      * [4] Get the next lock
      */
     lock = waiter->lock;
     /*
      * [5] We need to trylock here as we are holding task->pi_lock,
      * which is the reverse lock order versus the other rtmutex
      * operations.
      */
     if (!raw_spin_trylock(&lock->wait_lock)) {
         raw_spin_unlock_irq(&task->pi_lock);
         cpu_relax();
         goto retry;
     }
 
     /*
      * [6] check_exit_conditions_2() protected by task->pi_lock and
      * lock->wait_lock.
      *
      * Deadlock detection. If the lock is the same as the original
      * lock which caused us to walk the lock chain or if the
      * current lock is owned by the task which initiated the chain
      * walk, we detected a deadlock.
      */
     if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
         ret = -EDEADLK;
 
         /*
          * When the deadlock is due to ww_mutex; also see above. Don't
          * report the deadlock and instead let the ww_mutex wound/die
          * logic pick which of the contending threads gets -EDEADLK.
          *
          * NOTE: assumes the cycle only contains a single ww_class; any
          * other configuration and we fail to report; also, see
          * lockdep.
          */
         if (IS_ENABLED(CONFIG_PREEMPT_RT) && orig_waiter && orig_waiter->ww_ctx)
             ret = 0;
 
         raw_spin_unlock(&lock->wait_lock);
         goto out_unlock_pi;
     }
 
     /*
      * If we just follow the lock chain for deadlock detection, no
      * need to do all the requeue operations. To avoid a truckload
      * of conditionals around the various places below, just do the
      * minimum chain walk checks.
      */
     if (!requeue) {
         /*
          * No requeue[7] here. Just release @task [8]
          */
         raw_spin_unlock(&task->pi_lock);
         put_task_struct(task);
 
         /*
          * [9] check_exit_conditions_3 protected by lock->wait_lock.
          * If there is no owner of the lock, end of chain.
          */
         if (!rt_mutex_owner(lock)) {
             raw_spin_unlock_irq(&lock->wait_lock);
             return 0;
         }
 
         /* [10] Grab the next task, i.e. owner of @lock */
         task = get_task_struct(rt_mutex_owner(lock));
         raw_spin_lock(&task->pi_lock);
 
         /*
          * No requeue [11] here. We just do deadlock detection.
          *
          * [12] Store whether owner is blocked
          * itself. Decision is made after dropping the locks
          */
         next_lock = task_blocked_on_lock(task);
         /*
          * Get the top waiter for the next iteration
          */
         top_waiter = rt_mutex_top_waiter(lock);
 
         /* [13] Drop locks */
         raw_spin_unlock(&task->pi_lock);
         raw_spin_unlock_irq(&lock->wait_lock);
 
         /* If owner is not blocked, end of chain. */
         if (!next_lock)
             goto out_put_task;
         goto again;
     }
 
     /*
      * Store the current top waiter before doing the requeue
      * operation on @lock. We need it for the boost/deboost
      * decision below.
      */
     prerequeue_top_waiter = rt_mutex_top_waiter(lock);
 
     /* [7] Requeue the waiter in the lock waiter tree. */
     rt_mutex_dequeue(lock, waiter);
 
     /*
      * Update the waiter prio fields now that we're dequeued.
      *
      * These values can have changed through either:
      *
      *   sys_sched_set_scheduler() / sys_sched_setattr()
      *
      * or
      *
      *   DL CBS enforcement advancing the effective deadline.
      *
      * Even though pi_waiters also uses these fields, and that tree is only
      * updated in [11], we can do this here, since we hold [L], which
      * serializes all pi_waiters access and rb_erase() does not care about
      * the values of the node being removed.
      */
     waiter_update_prio(waiter, task);
 
     rt_mutex_enqueue(lock, waiter);
 
     /* [8] Release the task */
     raw_spin_unlock(&task->pi_lock);
     put_task_struct(task);
 
     /*
      * [9] check_exit_conditions_3 protected by lock->wait_lock.
      *
      * We must abort the chain walk if there is no lock owner even
      * in the dead lock detection case, as we have nothing to
      * follow here. This is the end of the chain we are walking.
      */
     if (!rt_mutex_owner(lock)) {
         /*
          * If the requeue [7] above changed the top waiter,
          * then we need to wake the new top waiter up to try
          * to get the lock.
          */
         if (prerequeue_top_waiter != rt_mutex_top_waiter(lock))
             wake_up_state(waiter->task, waiter->wake_state);
         raw_spin_unlock_irq(&lock->wait_lock);
         return 0;
     }
 
     /* [10] Grab the next task, i.e. the owner of @lock */
     task = get_task_struct(rt_mutex_owner(lock));
     raw_spin_lock(&task->pi_lock);
 
     /* [11] requeue the pi waiters if necessary */
     if (waiter == rt_mutex_top_waiter(lock)) {
         /*
          * The waiter became the new top (highest priority)
          * waiter on the lock. Replace the previous top waiter
          * in the owner tasks pi waiters tree with this waiter
          * and adjust the priority of the owner.
          */
         rt_mutex_dequeue_pi(task, prerequeue_top_waiter);
         rt_mutex_enqueue_pi(task, waiter);
         rt_mutex_adjust_prio(task);
 
     } else if (prerequeue_top_waiter == waiter) {
         /*
          * The waiter was the top waiter on the lock, but is
          * no longer the top priority waiter. Replace waiter in
          * the owner tasks pi waiters tree with the new top
          * (highest priority) waiter and adjust the priority
          * of the owner.
          * The new top waiter is stored in @waiter so that
          * @waiter == @top_waiter evaluates to true below and
          * we continue to deboost the rest of the chain.
          */
         rt_mutex_dequeue_pi(task, waiter);
         waiter = rt_mutex_top_waiter(lock);
         rt_mutex_enqueue_pi(task, waiter);
         rt_mutex_adjust_prio(task);
     } else {
         /*
          * Nothing changed. No need to do any priority
          * adjustment.
          */
     }
 
     /*
      * [12] check_exit_conditions_4() protected by task->pi_lock
      * and lock->wait_lock. The actual decisions are made after we
      * dropped the locks.
      *
      * Check whether the task which owns the current lock is pi
      * blocked itself. If yes we store a pointer to the lock for
      * the lock chain change detection above. After we dropped
      * task->pi_lock next_lock cannot be dereferenced anymore.
      */
     next_lock = task_blocked_on_lock(task);
     /*
      * Store the top waiter of @lock for the end of chain walk
      * decision below.
      */
     top_waiter = rt_mutex_top_waiter(lock);
 
     /* [13] Drop the locks */
     raw_spin_unlock(&task->pi_lock);
     raw_spin_unlock_irq(&lock->wait_lock);
 
     /*
      * Make the actual exit decisions [12], based on the stored
      * values.
      *
      * We reached the end of the lock chain. Stop right here. No
      * point to go back just to figure that out.
      */
     if (!next_lock)
         goto out_put_task;
 
     /*
      * If the current waiter is not the top waiter on the lock,
      * then we can stop the chain walk here if we are not in full
      * deadlock detection mode.
      */
     if (!detect_deadlock && waiter != top_waiter)
         goto out_put_task;
 
     goto again;
 
  out_unlock_pi:
     raw_spin_unlock_irq(&task->pi_lock);
  out_put_task:
     put_task_struct(task);
 
     return ret;
 }
 
 /*
  * Try to take an rt-mutex
  *
  * Must be called with lock->wait_lock held and interrupts disabled
  *
  * @lock:   The lock to be acquired.
  * @task:   The task which wants to acquire the lock
  * @waiter: The waiter that is queued to the lock's wait tree if the
  *      callsite called task_blocked_on_lock(), otherwise NULL
  */
 static int __sched
 try_to_take_rt_mutex(struct rt_mutex_base *lock, struct task_struct *task,
              struct rt_mutex_waiter *waiter)
 {
     lockdep_assert_held(&lock->wait_lock);
 
     /*
      * Before testing whether we can acquire @lock, we set the
      * RT_MUTEX_HAS_WAITERS bit in @lock->owner. This forces all
      * other tasks which try to modify @lock into the slow path
      * and they serialize on @lock->wait_lock.
      *
      * The RT_MUTEX_HAS_WAITERS bit can have a transitional state
      * as explained at the top of this file if and only if:
      *
      * - There is a lock owner. The caller must fixup the
      *   transient state if it does a trylock or leaves the lock
      *   function due to a signal or timeout.
      *
      * - @task acquires the lock and there are no other
      *   waiters. This is undone in rt_mutex_set_owner(@task) at
      *   the end of this function.
      */
     mark_rt_mutex_waiters(lock);
 
     /*
      * If @lock has an owner, give up.
      */
     if (rt_mutex_owner(lock))
         return 0;
 
     /*
      * If @waiter != NULL, @task has already enqueued the waiter
      * into @lock waiter tree. If @waiter == NULL then this is a
      * trylock attempt.
      */
     if (waiter) {
         struct rt_mutex_waiter *top_waiter = rt_mutex_top_waiter(lock);
 
         /*
          * If waiter is the highest priority waiter of @lock,
          * or allowed to steal it, take it over.
          */
         if (waiter == top_waiter || rt_mutex_steal(waiter, top_waiter)) {
             /*
              * We can acquire the lock. Remove the waiter from the
              * lock waiters tree.
              */
             rt_mutex_dequeue(lock, waiter);
         } else {
             return 0;
         }
     } else {
         /*
          * If the lock has waiters already we check whether @task is
          * eligible to take over the lock.
          *
          * If there are no other waiters, @task can acquire
          * the lock.  @task->pi_blocked_on is NULL, so it does
          * not need to be dequeued.
          */
         if (rt_mutex_has_waiters(lock)) {
             /* Check whether the trylock can steal it. */
             if (!rt_mutex_steal(task_to_waiter(task),
                         rt_mutex_top_waiter(lock)))
                 return 0;
 
             /*
              * The current top waiter stays enqueued. We
              * don't have to change anything in the lock
              * waiters order.
              */
         } else {
             /*
              * No waiters. Take the lock without the
              * pi_lock dance.@task->pi_blocked_on is NULL
              * and we have no waiters to enqueue in @task
              * pi waiters tree.
              */
             goto takeit;
         }
     }
 
     /*
      * Clear @task->pi_blocked_on. Requires protection by
      * @task->pi_lock. Redundant operation for the @waiter == NULL
      * case, but conditionals are more expensive than a redundant
      * store.
      */
     raw_spin_lock(&task->pi_lock);
     task->pi_blocked_on = NULL;
     /*
      * Finish the lock acquisition. @task is the new owner. If
      * other waiters exist we have to insert the highest priority
      * waiter into @task->pi_waiters tree.
      */
     if (rt_mutex_has_waiters(lock))
         rt_mutex_enqueue_pi(task, rt_mutex_top_waiter(lock));
     raw_spin_unlock(&task->pi_lock);
 
 takeit:
     /*
      * This either preserves the RT_MUTEX_HAS_WAITERS bit if there
      * are still waiters or clears it.
      */
     rt_mutex_set_owner(lock, task);
 
     return 1;
 }
 
 /*
  * Task blocks on lock.
  *
  * Prepare waiter and propagate pi chain
  *
  * This must be called with lock->wait_lock held and interrupts disabled
  */
 static int __sched task_blocks_on_rt_mutex(struct rt_mutex_base *lock,
                        struct rt_mutex_waiter *waiter,
                        struct task_struct *task,
                        struct ww_acquire_ctx *ww_ctx,
                        enum rtmutex_chainwalk chwalk)
 {
     struct task_struct *owner = rt_mutex_owner(lock);
     struct rt_mutex_waiter *top_waiter = waiter;
     struct rt_mutex_base *next_lock;
     int chain_walk = 0, res;
 
     lockdep_assert_held(&lock->wait_lock);
 
     /*
      * Early deadlock detection. We really don't want the task to
      * enqueue on itself just to untangle the mess later. It's not
      * only an optimization. We drop the locks, so another waiter
      * can come in before the chain walk detects the deadlock. So
      * the other will detect the deadlock and return -EDEADLOCK,
      * which is wrong, as the other waiter is not in a deadlock
      * situation.
      *
      * Except for ww_mutex, in that case the chain walk must already deal
      * with spurious cycles, see the comments at [3] and [6].
      */
     if (owner == task && !(build_ww_mutex() && ww_ctx))
         return -EDEADLK;
 
     raw_spin_lock(&task->pi_lock);
     waiter->task = task;
     waiter->lock = lock;
     waiter_update_prio(waiter, task);
 
     /* Get the top priority waiter on the lock */
     if (rt_mutex_has_waiters(lock))
         top_waiter = rt_mutex_top_waiter(lock);
     rt_mutex_enqueue(lock, waiter);
 
     task->pi_blocked_on = waiter;
 
     raw_spin_unlock(&task->pi_lock);
 
     if (build_ww_mutex() && ww_ctx) {
         struct rt_mutex *rtm;
 
         /* Check whether the waiter should back out immediately */
         rtm = container_of(lock, struct rt_mutex, rtmutex);
         res = __ww_mutex_add_waiter(waiter, rtm, ww_ctx);
         if (res) {
             raw_spin_lock(&task->pi_lock);
             rt_mutex_dequeue(lock, waiter);
             task->pi_blocked_on = NULL;
             raw_spin_unlock(&task->pi_lock);
             return res;
         }
     }
 
     if (!owner)
         return 0;
 
     raw_spin_lock(&owner->pi_lock);
     if (waiter == rt_mutex_top_waiter(lock)) {
         rt_mutex_dequeue_pi(owner, top_waiter);
         rt_mutex_enqueue_pi(owner, waiter);
 
         rt_mutex_adjust_prio(owner);
         if (owner->pi_blocked_on)
             chain_walk = 1;
     } else if (rt_mutex_cond_detect_deadlock(waiter, chwalk)) {
         chain_walk = 1;
     }
 
     /* Store the lock on which owner is blocked or NULL */
     next_lock = task_blocked_on_lock(owner);
 
     raw_spin_unlock(&owner->pi_lock);
     /*
      * Even if full deadlock detection is on, if the owner is not
      * blocked itself, we can avoid finding this out in the chain
      * walk.
      */
     if (!chain_walk || !next_lock)
         return 0;
 
     /*
      * The owner can't disappear while holding a lock,
      * so the owner struct is protected by wait_lock.
      * Gets dropped in rt_mutex_adjust_prio_chain()!
      */
     get_task_struct(owner);
 
     raw_spin_unlock_irq(&lock->wait_lock);
 
     res = rt_mutex_adjust_prio_chain(owner, chwalk, lock,
                      next_lock, waiter, task);
 
     raw_spin_lock_irq(&lock->wait_lock);
 
     return res;
 }
 
 /*
  * Remove the top waiter from the current tasks pi waiter tree and
  * queue it up.
  *
  * Called with lock->wait_lock held and interrupts disabled.
  */
 static void __sched mark_wakeup_next_waiter(struct rt_wake_q_head *wqh,
                         struct rt_mutex_base *lock)
 {
     struct rt_mutex_waiter *waiter;
 
     raw_spin_lock(&current->pi_lock);
 
     waiter = rt_mutex_top_waiter(lock);
 
     /*
      * Remove it from current->pi_waiters and deboost.
      *
      * We must in fact deboost here in order to ensure we call
      * rt_mutex_setprio() to update p->pi_top_task before the
      * task unblocks.
      */
     rt_mutex_dequeue_pi(current, waiter);
     rt_mutex_adjust_prio(current);
 
     /*
      * As we are waking up the top waiter, and the waiter stays
      * queued on the lock until it gets the lock, this lock
      * obviously has waiters. Just set the bit here and this has
      * the added benefit of forcing all new tasks into the
      * slow path making sure no task of lower priority than
      * the top waiter can steal this lock.
      */
     lock->owner = (void *) RT_MUTEX_HAS_WAITERS;
 
     /*
      * We deboosted before waking the top waiter task such that we don't
      * run two tasks with the 'same' priority (and ensure the
      * p->pi_top_task pointer points to a blocked task). This however can
      * lead to priority inversion if we would get preempted after the
      * deboost but before waking our donor task, hence the preempt_disable()
      * before unlock.
      *
      * Pairs with preempt_enable() in rt_mutex_wake_up_q();
      */
     preempt_disable();
     rt_mutex_wake_q_add(wqh, waiter);
     raw_spin_unlock(&current->pi_lock);
 }
 
 static int __sched __rt_mutex_slowtrylock(struct rt_mutex_base *lock)
 {
     int ret = try_to_take_rt_mutex(lock, current, NULL);
 
     /*
      * try_to_take_rt_mutex() sets the lock waiters bit
      * unconditionally. Clean this up.
      */
     fixup_rt_mutex_waiters(lock);
 
     return ret;
 }
 
 /*
  * Slow path try-lock function:
  */
 static int __sched rt_mutex_slowtrylock(struct rt_mutex_base *lock)
 {
     unsigned long flags;
     int ret;
 
     /*
      * If the lock already has an owner we fail to get the lock.
      * This can be done without taking the @lock->wait_lock as
      * it is only being read, and this is a trylock anyway.
      */
     if (rt_mutex_owner(lock))
         return 0;
 
     /*
      * The mutex has currently no owner. Lock the wait lock and try to
      * acquire the lock. We use irqsave here to support early boot calls.
      */
     raw_spin_lock_irqsave(&lock->wait_lock, flags);
 
     ret = __rt_mutex_slowtrylock(lock);
 
     raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
 
     return ret;
 }
 
 static __always_inline int __rt_mutex_trylock(struct rt_mutex_base *lock)
 {
     if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
         return 1;
 
     return rt_mutex_slowtrylock(lock);
 }
 
 /*
  * Slow path to release a rt-mutex.
  */
 static void __sched rt_mutex_slowunlock(struct rt_mutex_base *lock)
 {
     DEFINE_RT_WAKE_Q(wqh);
     unsigned long flags;
 
     /* irqsave required to support early boot calls */
     raw_spin_lock_irqsave(&lock->wait_lock, flags);
 
     debug_rt_mutex_unlock(lock);
 
     /*
      * We must be careful here if the fast path is enabled. If we
      * have no waiters queued we cannot set owner to NULL here
      * because of:
      *
      * foo->lock->owner = NULL;
      *          rtmutex_lock(foo->lock);   <- fast path
      *          free = atomic_dec_and_test(foo->refcnt);
      *          rtmutex_unlock(foo->lock); <- fast path
      *          if (free)
      *              kfree(foo);
      * raw_spin_unlock(foo->lock->wait_lock);
      *
      * So for the fastpath enabled kernel:
      *
      * Nothing can set the waiters bit as long as we hold
      * lock->wait_lock. So we do the following sequence:
      *
      *  owner = rt_mutex_owner(lock);
      *  clear_rt_mutex_waiters(lock);
      *  raw_spin_unlock(&lock->wait_lock);
      *  if (cmpxchg(&lock->owner, owner, 0) == owner)
      *      return;
      *  goto retry;
      *
      * The fastpath disabled variant is simple as all access to
      * lock->owner is serialized by lock->wait_lock:
      *
      *  lock->owner = NULL;
      *  raw_spin_unlock(&lock->wait_lock);
      */
     while (!rt_mutex_has_waiters(lock)) {
         /* Drops lock->wait_lock ! */
         if (unlock_rt_mutex_safe(lock, flags) == true)
             return;
         /* Relock the rtmutex and try again */
         raw_spin_lock_irqsave(&lock->wait_lock, flags);
     }
 
     /*
      * The wakeup next waiter path does not suffer from the above
      * race. See the comments there.
      *
      * Queue the next waiter for wakeup once we release the wait_lock.
      */
     mark_wakeup_next_waiter(&wqh, lock);
     raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
 
     rt_mutex_wake_up_q(&wqh);
 }
 
 static __always_inline void __rt_mutex_unlock(struct rt_mutex_base *lock)
 {
     if (likely(rt_mutex_cmpxchg_release(lock, current, NULL)))
         return;
 
     rt_mutex_slowunlock(lock);
 }
 
 #ifdef CONFIG_SMP
 static bool rtmutex_spin_on_owner(struct rt_mutex_base *lock,
                   struct rt_mutex_waiter *waiter,
                   struct task_struct *owner)
 {
     bool res = true;
 
     rcu_read_lock();
     for (;;) {
         /* If owner changed, trylock again. */
         if (owner != rt_mutex_owner(lock))
             break;
         /*
          * Ensure that @owner is dereferenced after checking that
          * the lock owner still matches @owner. If that fails,
          * @owner might point to freed memory. If it still matches,
          * the rcu_read_lock() ensures the memory stays valid.
          */
         barrier();
         /*
          * Stop spinning when:
          *  - the lock owner has been scheduled out
          *  - current is not longer the top waiter
          *  - current is requested to reschedule (redundant
          *    for CONFIG_PREEMPT_RCU=y)
          *  - the VCPU on which owner runs is preempted
          */
         if (!owner_on_cpu(owner) || need_resched() ||
             !rt_mutex_waiter_is_top_waiter(lock, waiter)) {
             res = false;
             break;
         }
         cpu_relax();
     }
     rcu_read_unlock();
     return res;
 }
 #else
 static bool rtmutex_spin_on_owner(struct rt_mutex_base *lock,
                   struct rt_mutex_waiter *waiter,
                   struct task_struct *owner)
 {
     return false;
 }
 #endif
 
 #ifdef RT_MUTEX_BUILD_MUTEX
 /*
  * Functions required for:
  *  - rtmutex, futex on all kernels
  *  - mutex and rwsem substitutions on RT kernels
  */
 
 /*
  * Remove a waiter from a lock and give up
  *
  * Must be called with lock->wait_lock held and interrupts disabled. It must
  * have just failed to try_to_take_rt_mutex().
  */
 static void __sched remove_waiter(struct rt_mutex_base *lock,
                   struct rt_mutex_waiter *waiter)
 {
     bool is_top_waiter = (waiter == rt_mutex_top_waiter(lock));
     struct task_struct *owner = rt_mutex_owner(lock);
     struct rt_mutex_base *next_lock;
 
     lockdep_assert_held(&lock->wait_lock);
 
     raw_spin_lock(&current->pi_lock);
     rt_mutex_dequeue(lock, waiter);
     current->pi_blocked_on = NULL;
     raw_spin_unlock(&current->pi_lock);
 
     /*
      * Only update priority if the waiter was the highest priority
      * waiter of the lock and there is an owner to update.
      */
     if (!owner || !is_top_waiter)
         return;
 
     raw_spin_lock(&owner->pi_lock);
 
     rt_mutex_dequeue_pi(owner, waiter);
 
     if (rt_mutex_has_waiters(lock))
         rt_mutex_enqueue_pi(owner, rt_mutex_top_waiter(lock));
 
     rt_mutex_adjust_prio(owner);
 
     /* Store the lock on which owner is blocked or NULL */
     next_lock = task_blocked_on_lock(owner);
 
     raw_spin_unlock(&owner->pi_lock);
 
     /*
      * Don't walk the chain, if the owner task is not blocked
      * itself.
      */
     if (!next_lock)
         return;
 
     /* gets dropped in rt_mutex_adjust_prio_chain()! */
     get_task_struct(owner);
 
     raw_spin_unlock_irq(&lock->wait_lock);
 
     rt_mutex_adjust_prio_chain(owner, RT_MUTEX_MIN_CHAINWALK, lock,
                    next_lock, NULL, current);
 
     raw_spin_lock_irq(&lock->wait_lock);
 }
 
 /**
  * rt_mutex_slowlock_block() - Perform the wait-wake-try-to-take loop
  * @lock:        the rt_mutex to take
  * @ww_ctx:      WW mutex context pointer
  * @state:       the state the task should block in (TASK_INTERRUPTIBLE
  *           or TASK_UNINTERRUPTIBLE)
  * @timeout:         the pre-initialized and started timer, or NULL for none
  * @waiter:      the pre-initialized rt_mutex_waiter
  *
  * Must be called with lock->wait_lock held and interrupts disabled
  */
 static int __sched rt_mutex_slowlock_block(struct rt_mutex_base *lock,
                        struct ww_acquire_ctx *ww_ctx,
                        unsigned int state,
                        struct hrtimer_sleeper *timeout,
                        struct rt_mutex_waiter *waiter)
 {
     struct rt_mutex *rtm = container_of(lock, struct rt_mutex, rtmutex);
     struct task_struct *owner;
     int ret = 0;
 
     for (;;) {
         /* Try to acquire the lock: */
         if (try_to_take_rt_mutex(lock, current, waiter))
             break;
 
         if (timeout && !timeout->task) {
             ret = -ETIMEDOUT;
             break;
         }
         if (signal_pending_state(state, current)) {
             ret = -EINTR;
             break;
         }
 
         if (build_ww_mutex() && ww_ctx) {
             ret = __ww_mutex_check_kill(rtm, waiter, ww_ctx);
             if (ret)
                 break;
         }
 
         if (waiter == rt_mutex_top_waiter(lock))
             owner = rt_mutex_owner(lock);
         else
             owner = NULL;
         raw_spin_unlock_irq(&lock->wait_lock);
 
         if (!owner || !rtmutex_spin_on_owner(lock, waiter, owner))
             schedule();
 
         raw_spin_lock_irq(&lock->wait_lock);
         set_current_state(state);
     }
 
     __set_current_state(TASK_RUNNING);
     return ret;
 }
 
 static void __sched rt_mutex_handle_deadlock(int res, int detect_deadlock,
                          struct rt_mutex_waiter *w)
 {
     /*
      * If the result is not -EDEADLOCK or the caller requested
      * deadlock detection, nothing to do here.
      */
     if (res != -EDEADLOCK || detect_deadlock)
         return;
 
     if (build_ww_mutex() && w->ww_ctx)
         return;
 
     /*
      * Yell loudly and stop the task right here.
      */
     WARN(1, "rtmutex deadlock detected\n");
     while (1) {
         set_current_state(TASK_INTERRUPTIBLE);
         schedule();
     }
 }
 
 /**
  * __rt_mutex_slowlock - Locking slowpath invoked with lock::wait_lock held
  * @lock:   The rtmutex to block lock
  * @ww_ctx: WW mutex context pointer
  * @state:  The task state for sleeping
  * @chwalk: Indicator whether full or partial chainwalk is requested
  * @waiter: Initializer waiter for blocking
  */
 static int __sched __rt_mutex_slowlock(struct rt_mutex_base *lock,
                        struct ww_acquire_ctx *ww_ctx,
                        unsigned int state,
                        enum rtmutex_chainwalk chwalk,
                        struct rt_mutex_waiter *waiter)
 {
     struct rt_mutex *rtm = container_of(lock, struct rt_mutex, rtmutex);
     struct ww_mutex *ww = ww_container_of(rtm);
     int ret;
 
     lockdep_assert_held(&lock->wait_lock);
 
     /* Try to acquire the lock again: */
     if (try_to_take_rt_mutex(lock, current, NULL)) {
         if (build_ww_mutex() && ww_ctx) {
             __ww_mutex_check_waiters(rtm, ww_ctx);
             ww_mutex_lock_acquired(ww, ww_ctx);
         }
         return 0;
     }
 
     set_current_state(state);
 
     trace_contention_begin(lock, LCB_F_RT);
 
     ret = task_blocks_on_rt_mutex(lock, waiter, current, ww_ctx, chwalk);
     if (likely(!ret))
         ret = rt_mutex_slowlock_block(lock, ww_ctx, state, NULL, waiter);
 
     if (likely(!ret)) {
         /* acquired the lock */
         if (build_ww_mutex() && ww_ctx) {
             if (!ww_ctx->is_wait_die)
                 __ww_mutex_check_waiters(rtm, ww_ctx);
             ww_mutex_lock_acquired(ww, ww_ctx);
         }
     } else {
         __set_current_state(TASK_RUNNING);
         remove_waiter(lock, waiter);
         rt_mutex_handle_deadlock(ret, chwalk, waiter);
     }
 
     /*
      * try_to_take_rt_mutex() sets the waiter bit
      * unconditionally. We might have to fix that up.
      */
     fixup_rt_mutex_waiters(lock);
 
     trace_contention_end(lock, ret);
 
     return ret;
 }
 
 static inline int __rt_mutex_slowlock_locked(struct rt_mutex_base *lock,
                          struct ww_acquire_ctx *ww_ctx,
                          unsigned int state)
 {
     struct rt_mutex_waiter waiter;
     int ret;
 
     rt_mutex_init_waiter(&waiter);
     waiter.ww_ctx = ww_ctx;
 
     ret = __rt_mutex_slowlock(lock, ww_ctx, state, RT_MUTEX_MIN_CHAINWALK,
                   &waiter);
 
     debug_rt_mutex_free_waiter(&waiter);
     return ret;
 }
 
 /*
  * rt_mutex_slowlock - Locking slowpath invoked when fast path fails
  * @lock:   The rtmutex to block lock
  * @ww_ctx: WW mutex context pointer
  * @state:  The task state for sleeping
  */
 static int __sched rt_mutex_slowlock(struct rt_mutex_base *lock,
                      struct ww_acquire_ctx *ww_ctx,
                      unsigned int state)
 {
     unsigned long flags;
     int ret;
 
     /*
      * Technically we could use raw_spin_[un]lock_irq() here, but this can
      * be called in early boot if the cmpxchg() fast path is disabled
      * (debug, no architecture support). In this case we will acquire the
      * rtmutex with lock->wait_lock held. But we cannot unconditionally
      * enable interrupts in that early boot case. So we need to use the
      * irqsave/restore variants.
      */
     raw_spin_lock_irqsave(&lock->wait_lock, flags);
     ret = __rt_mutex_slowlock_locked(lock, ww_ctx, state);
     raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
 
     return ret;
 }
 
 static __always_inline int __rt_mutex_lock(struct rt_mutex_base *lock,
                        unsigned int state)
 {
     if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
         return 0;
 
     return rt_mutex_slowlock(lock, NULL, state);
 }
 #endif /* RT_MUTEX_BUILD_MUTEX */
 
 #ifdef RT_MUTEX_BUILD_SPINLOCKS
 /*
  * Functions required for spin/rw_lock substitution on RT kernels
  */
 
 /**
  * rtlock_slowlock_locked - Slow path lock acquisition for RT locks
  * @lock:   The underlying RT mutex
  */
 static void __sched rtlock_slowlock_locked(struct rt_mutex_base *lock)
 {
     struct rt_mutex_waiter waiter;
     struct task_struct *owner;
 
     lockdep_assert_held(&lock->wait_lock);
 
     if (try_to_take_rt_mutex(lock, current, NULL))
         return;
 
     rt_mutex_init_rtlock_waiter(&waiter);
 
     /* Save current state and set state to TASK_RTLOCK_WAIT */
     current_save_and_set_rtlock_wait_state();
 
     trace_contention_begin(lock, LCB_F_RT);
 
     task_blocks_on_rt_mutex(lock, &waiter, current, NULL, RT_MUTEX_MIN_CHAINWALK);
 
     for (;;) {
         /* Try to acquire the lock again */
         if (try_to_take_rt_mutex(lock, current, &waiter))
             break;
 
         if (&waiter == rt_mutex_top_waiter(lock))
             owner = rt_mutex_owner(lock);
         else
             owner = NULL;
         raw_spin_unlock_irq(&lock->wait_lock);
 
         if (!owner || !rtmutex_spin_on_owner(lock, &waiter, owner))
             schedule_rtlock();
 
         raw_spin_lock_irq(&lock->wait_lock);
         set_current_state(TASK_RTLOCK_WAIT);
     }
 
     /* Restore the task state */
     current_restore_rtlock_saved_state();
 
     /*
      * try_to_take_rt_mutex() sets the waiter bit unconditionally.
      * We might have to fix that up:
      */
     fixup_rt_mutex_waiters(lock);
     debug_rt_mutex_free_waiter(&waiter);
 
     trace_contention_end(lock, 0);
 }
 
 static __always_inline void __sched rtlock_slowlock(struct rt_mutex_base *lock)
 {
     unsigned long flags;
 
     raw_spin_lock_irqsave(&lock->wait_lock, flags);
     rtlock_slowlock_locked(lock);
     raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
 }
 
 #endif /* RT_MUTEX_BUILD_SPINLOCKS */

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