v4.19.13 snapshot.
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
new file mode 100644
index 0000000..2823d41
--- /dev/null
+++ b/kernel/locking/rtmutex.c
@@ -0,0 +1,1897 @@
+/*
+ * 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
+ *
+ * See Documentation/locking/rt-mutex-design.txt for details.
+ */
+#include <linux/spinlock.h>
+#include <linux/export.h>
+#include <linux/sched/signal.h>
+#include <linux/sched/rt.h>
+#include <linux/sched/deadline.h>
+#include <linux/sched/wake_q.h>
+#include <linux/sched/debug.h>
+#include <linux/timer.h>
+
+#include "rtmutex_common.h"
+
+/*
+ * 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 void
+rt_mutex_set_owner(struct rt_mutex *lock, struct task_struct *owner)
+{
+ unsigned long val = (unsigned long)owner;
+
+ if (rt_mutex_has_waiters(lock))
+ val |= RT_MUTEX_HAS_WAITERS;
+
+ lock->owner = (struct task_struct *)val;
+}
+
+static inline void clear_rt_mutex_waiters(struct rt_mutex *lock)
+{
+ lock->owner = (struct task_struct *)
+ ((unsigned long)lock->owner & ~RT_MUTEX_HAS_WAITERS);
+}
+
+static void fixup_rt_mutex_waiters(struct rt_mutex *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
+# define rt_mutex_cmpxchg_relaxed(l,c,n) (cmpxchg_relaxed(&l->owner, c, n) == c)
+# define rt_mutex_cmpxchg_acquire(l,c,n) (cmpxchg_acquire(&l->owner, c, n) == c)
+# define rt_mutex_cmpxchg_release(l,c,n) (cmpxchg_release(&l->owner, c, n) == c)
+
+/*
+ * 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 inline void mark_rt_mutex_waiters(struct rt_mutex *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 inline bool unlock_rt_mutex_safe(struct rt_mutex *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
+# define rt_mutex_cmpxchg_relaxed(l,c,n) (0)
+# define rt_mutex_cmpxchg_acquire(l,c,n) (0)
+# define rt_mutex_cmpxchg_release(l,c,n) (0)
+
+static inline void mark_rt_mutex_waiters(struct rt_mutex *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 inline bool unlock_rt_mutex_safe(struct rt_mutex *lock,
+ unsigned long flags)
+ __releases(lock->wait_lock)
+{
+ lock->owner = NULL;
+ raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
+ return true;
+}
+#endif
+
+/*
+ * Only use with rt_mutex_waiter_{less,equal}()
+ */
+#define task_to_waiter(p) \
+ &(struct rt_mutex_waiter){ .prio = (p)->prio, .deadline = (p)->dl.deadline }
+
+static 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 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 void
+rt_mutex_enqueue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
+{
+ struct rb_node **link = &lock->waiters.rb_root.rb_node;
+ struct rb_node *parent = NULL;
+ struct rt_mutex_waiter *entry;
+ bool leftmost = true;
+
+ while (*link) {
+ parent = *link;
+ entry = rb_entry(parent, struct rt_mutex_waiter, tree_entry);
+ if (rt_mutex_waiter_less(waiter, entry)) {
+ link = &parent->rb_left;
+ } else {
+ link = &parent->rb_right;
+ leftmost = false;
+ }
+ }
+
+ rb_link_node(&waiter->tree_entry, parent, link);
+ rb_insert_color_cached(&waiter->tree_entry, &lock->waiters, leftmost);
+}
+
+static void
+rt_mutex_dequeue(struct rt_mutex *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);
+}
+
+static void
+rt_mutex_enqueue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
+{
+ struct rb_node **link = &task->pi_waiters.rb_root.rb_node;
+ struct rb_node *parent = NULL;
+ struct rt_mutex_waiter *entry;
+ bool leftmost = true;
+
+ while (*link) {
+ parent = *link;
+ entry = rb_entry(parent, struct rt_mutex_waiter, pi_tree_entry);
+ if (rt_mutex_waiter_less(waiter, entry)) {
+ link = &parent->rb_left;
+ } else {
+ link = &parent->rb_right;
+ leftmost = false;
+ }
+ }
+
+ rb_link_node(&waiter->pi_tree_entry, parent, link);
+ rb_insert_color_cached(&waiter->pi_tree_entry, &task->pi_waiters, leftmost);
+}
+
+static 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 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);
+}
+
+/*
+ * 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 bool rt_mutex_cond_detect_deadlock(struct rt_mutex_waiter *waiter,
+ enum rtmutex_chainwalk chwalk)
+{
+ /*
+ * This is just a wrapper function for the following call,
+ * because debug_rt_mutex_detect_deadlock() smells like a magic
+ * debug feature and I wanted to keep the cond function in the
+ * main source file along with the comments instead of having
+ * two of the same in the headers.
+ */
+ return debug_rt_mutex_detect_deadlock(waiter, chwalk);
+}
+
+/*
+ * Max number of times we'll walk the boosting chain:
+ */
+int max_lock_depth = 1024;
+
+static inline struct rt_mutex *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 rt_mutex_adjust_prio_chain(struct task_struct *task,
+ enum rtmutex_chainwalk chwalk,
+ struct rt_mutex *orig_lock,
+ struct rt_mutex *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 *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;
+
+ /*
+ * 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) {
+ debug_rt_mutex_deadlock(chwalk, orig_waiter, lock);
+ raw_spin_unlock(&lock->wait_lock);
+ ret = -EDEADLK;
+ 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 = rt_mutex_owner(lock);
+ get_task_struct(task);
+ 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->prio = task->prio;
+ waiter->deadline = task->dl.deadline;
+
+ 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_process(rt_mutex_top_waiter(lock)->task);
+ raw_spin_unlock_irq(&lock->wait_lock);
+ return 0;
+ }
+
+ /* [10] Grab the next task, i.e. the owner of @lock */
+ task = rt_mutex_owner(lock);
+ get_task_struct(task);
+ 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 prority 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 try_to_take_rt_mutex(struct rt_mutex *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) {
+ /*
+ * If waiter is not the highest priority waiter of
+ * @lock, give up.
+ */
+ if (waiter != rt_mutex_top_waiter(lock))
+ return 0;
+
+ /*
+ * We can acquire the lock. Remove the waiter from the
+ * lock waiters tree.
+ */
+ rt_mutex_dequeue(lock, waiter);
+
+ } 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)) {
+ /*
+ * If @task->prio is greater than or equal to
+ * the top waiter priority (kernel view),
+ * @task lost.
+ */
+ if (!rt_mutex_waiter_less(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:
+ /* We got the lock. */
+ debug_rt_mutex_lock(lock);
+
+ /*
+ * 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 task_blocks_on_rt_mutex(struct rt_mutex *lock,
+ struct rt_mutex_waiter *waiter,
+ struct task_struct *task,
+ enum rtmutex_chainwalk chwalk)
+{
+ struct task_struct *owner = rt_mutex_owner(lock);
+ struct rt_mutex_waiter *top_waiter = waiter;
+ struct rt_mutex *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.
+ */
+ if (owner == task)
+ return -EDEADLK;
+
+ raw_spin_lock(&task->pi_lock);
+ waiter->task = task;
+ waiter->lock = lock;
+ waiter->prio = task->prio;
+ waiter->deadline = task->dl.deadline;
+
+ /* 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 (!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 mark_wakeup_next_waiter(struct wake_q_head *wake_q,
+ struct rt_mutex *lock)
+{
+ struct rt_mutex_waiter *waiter;
+
+ raw_spin_lock(¤t->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_postunlock();
+ */
+ preempt_disable();
+ wake_q_add(wake_q, waiter->task);
+ raw_spin_unlock(¤t->pi_lock);
+}
+
+/*
+ * Remove a waiter from a lock and give up
+ *
+ * Must be called with lock->wait_lock held and interrupts disabled. I must
+ * have just failed to try_to_take_rt_mutex().
+ */
+static void remove_waiter(struct rt_mutex *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 *next_lock;
+
+ lockdep_assert_held(&lock->wait_lock);
+
+ raw_spin_lock(¤t->pi_lock);
+ rt_mutex_dequeue(lock, waiter);
+ current->pi_blocked_on = NULL;
+ raw_spin_unlock(¤t->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);
+}
+
+/*
+ * Recheck the pi chain, in case we got a priority setting
+ *
+ * Called from sched_setscheduler
+ */
+void rt_mutex_adjust_pi(struct task_struct *task)
+{
+ struct rt_mutex_waiter *waiter;
+ struct rt_mutex *next_lock;
+ unsigned long flags;
+
+ raw_spin_lock_irqsave(&task->pi_lock, flags);
+
+ waiter = task->pi_blocked_on;
+ if (!waiter || rt_mutex_waiter_equal(waiter, task_to_waiter(task))) {
+ raw_spin_unlock_irqrestore(&task->pi_lock, flags);
+ return;
+ }
+ next_lock = waiter->lock;
+ raw_spin_unlock_irqrestore(&task->pi_lock, flags);
+
+ /* gets dropped in rt_mutex_adjust_prio_chain()! */
+ get_task_struct(task);
+
+ rt_mutex_adjust_prio_chain(task, RT_MUTEX_MIN_CHAINWALK, NULL,
+ next_lock, NULL, task);
+}
+
+void rt_mutex_init_waiter(struct rt_mutex_waiter *waiter)
+{
+ debug_rt_mutex_init_waiter(waiter);
+ RB_CLEAR_NODE(&waiter->pi_tree_entry);
+ RB_CLEAR_NODE(&waiter->tree_entry);
+ waiter->task = NULL;
+}
+
+/**
+ * __rt_mutex_slowlock() - Perform the wait-wake-try-to-take loop
+ * @lock: the rt_mutex to take
+ * @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(struct rt_mutex *lock, int state,
+ struct hrtimer_sleeper *timeout,
+ struct rt_mutex_waiter *waiter)
+{
+ int ret = 0;
+
+ for (;;) {
+ /* Try to acquire the lock: */
+ if (try_to_take_rt_mutex(lock, current, waiter))
+ break;
+
+ /*
+ * TASK_INTERRUPTIBLE checks for signals and
+ * timeout. Ignored otherwise.
+ */
+ if (likely(state == TASK_INTERRUPTIBLE)) {
+ /* Signal pending? */
+ if (signal_pending(current))
+ ret = -EINTR;
+ if (timeout && !timeout->task)
+ ret = -ETIMEDOUT;
+ if (ret)
+ break;
+ }
+
+ raw_spin_unlock_irq(&lock->wait_lock);
+
+ debug_rt_mutex_print_deadlock(waiter);
+
+ schedule();
+
+ raw_spin_lock_irq(&lock->wait_lock);
+ set_current_state(state);
+ }
+
+ __set_current_state(TASK_RUNNING);
+ return ret;
+}
+
+static void 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;
+
+ /*
+ * Yell lowdly and stop the task right here.
+ */
+ rt_mutex_print_deadlock(w);
+ while (1) {
+ set_current_state(TASK_INTERRUPTIBLE);
+ schedule();
+ }
+}
+
+/*
+ * Slow path lock function:
+ */
+static int __sched
+rt_mutex_slowlock(struct rt_mutex *lock, int state,
+ struct hrtimer_sleeper *timeout,
+ enum rtmutex_chainwalk chwalk)
+{
+ struct rt_mutex_waiter waiter;
+ unsigned long flags;
+ int ret = 0;
+
+ rt_mutex_init_waiter(&waiter);
+
+ /*
+ * 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);
+
+ /* Try to acquire the lock again: */
+ if (try_to_take_rt_mutex(lock, current, NULL)) {
+ raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
+ return 0;
+ }
+
+ set_current_state(state);
+
+ /* Setup the timer, when timeout != NULL */
+ if (unlikely(timeout))
+ hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
+
+ ret = task_blocks_on_rt_mutex(lock, &waiter, current, chwalk);
+
+ if (likely(!ret))
+ /* sleep on the mutex */
+ ret = __rt_mutex_slowlock(lock, state, timeout, &waiter);
+
+ if (unlikely(ret)) {
+ __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);
+
+ raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
+
+ /* Remove pending timer: */
+ if (unlikely(timeout))
+ hrtimer_cancel(&timeout->timer);
+
+ debug_rt_mutex_free_waiter(&waiter);
+
+ return ret;
+}
+
+static inline int __rt_mutex_slowtrylock(struct rt_mutex *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 inline int rt_mutex_slowtrylock(struct rt_mutex *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;
+}
+
+/*
+ * Slow path to release a rt-mutex.
+ *
+ * Return whether the current task needs to call rt_mutex_postunlock().
+ */
+static bool __sched rt_mutex_slowunlock(struct rt_mutex *lock,
+ struct wake_q_head *wake_q)
+{
+ 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 false;
+ /* 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(wake_q, lock);
+ raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
+
+ return true; /* call rt_mutex_postunlock() */
+}
+
+/*
+ * debug aware fast / slowpath lock,trylock,unlock
+ *
+ * The atomic acquire/release ops are compiled away, when either the
+ * architecture does not support cmpxchg or when debugging is enabled.
+ */
+static inline int
+rt_mutex_fastlock(struct rt_mutex *lock, int state,
+ int (*slowfn)(struct rt_mutex *lock, int state,
+ struct hrtimer_sleeper *timeout,
+ enum rtmutex_chainwalk chwalk))
+{
+ if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
+ return 0;
+
+ return slowfn(lock, state, NULL, RT_MUTEX_MIN_CHAINWALK);
+}
+
+static inline int
+rt_mutex_timed_fastlock(struct rt_mutex *lock, int state,
+ struct hrtimer_sleeper *timeout,
+ enum rtmutex_chainwalk chwalk,
+ int (*slowfn)(struct rt_mutex *lock, int state,
+ struct hrtimer_sleeper *timeout,
+ enum rtmutex_chainwalk chwalk))
+{
+ if (chwalk == RT_MUTEX_MIN_CHAINWALK &&
+ likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
+ return 0;
+
+ return slowfn(lock, state, timeout, chwalk);
+}
+
+static inline int
+rt_mutex_fasttrylock(struct rt_mutex *lock,
+ int (*slowfn)(struct rt_mutex *lock))
+{
+ if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
+ return 1;
+
+ return slowfn(lock);
+}
+
+/*
+ * Performs the wakeup of the the top-waiter and re-enables preemption.
+ */
+void rt_mutex_postunlock(struct wake_q_head *wake_q)
+{
+ wake_up_q(wake_q);
+
+ /* Pairs with preempt_disable() in rt_mutex_slowunlock() */
+ preempt_enable();
+}
+
+static inline void
+rt_mutex_fastunlock(struct rt_mutex *lock,
+ bool (*slowfn)(struct rt_mutex *lock,
+ struct wake_q_head *wqh))
+{
+ DEFINE_WAKE_Q(wake_q);
+
+ if (likely(rt_mutex_cmpxchg_release(lock, current, NULL)))
+ return;
+
+ if (slowfn(lock, &wake_q))
+ rt_mutex_postunlock(&wake_q);
+}
+
+static inline void __rt_mutex_lock(struct rt_mutex *lock, unsigned int subclass)
+{
+ might_sleep();
+
+ mutex_acquire(&lock->dep_map, subclass, 0, _RET_IP_);
+ rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, rt_mutex_slowlock);
+}
+
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+/**
+ * rt_mutex_lock_nested - lock a rt_mutex
+ *
+ * @lock: the rt_mutex to be locked
+ * @subclass: the lockdep subclass
+ */
+void __sched rt_mutex_lock_nested(struct rt_mutex *lock, unsigned int subclass)
+{
+ __rt_mutex_lock(lock, subclass);
+}
+EXPORT_SYMBOL_GPL(rt_mutex_lock_nested);
+#endif
+
+#ifndef CONFIG_DEBUG_LOCK_ALLOC
+/**
+ * rt_mutex_lock - lock a rt_mutex
+ *
+ * @lock: the rt_mutex to be locked
+ */
+void __sched rt_mutex_lock(struct rt_mutex *lock)
+{
+ __rt_mutex_lock(lock, 0);
+}
+EXPORT_SYMBOL_GPL(rt_mutex_lock);
+#endif
+
+/**
+ * rt_mutex_lock_interruptible - lock a rt_mutex interruptible
+ *
+ * @lock: the rt_mutex to be locked
+ *
+ * Returns:
+ * 0 on success
+ * -EINTR when interrupted by a signal
+ */
+int __sched rt_mutex_lock_interruptible(struct rt_mutex *lock)
+{
+ int ret;
+
+ might_sleep();
+
+ mutex_acquire(&lock->dep_map, 0, 0, _RET_IP_);
+ ret = rt_mutex_fastlock(lock, TASK_INTERRUPTIBLE, rt_mutex_slowlock);
+ if (ret)
+ mutex_release(&lock->dep_map, 1, _RET_IP_);
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible);
+
+/*
+ * Futex variant, must not use fastpath.
+ */
+int __sched rt_mutex_futex_trylock(struct rt_mutex *lock)
+{
+ return rt_mutex_slowtrylock(lock);
+}
+
+int __sched __rt_mutex_futex_trylock(struct rt_mutex *lock)
+{
+ return __rt_mutex_slowtrylock(lock);
+}
+
+/**
+ * rt_mutex_timed_lock - lock a rt_mutex interruptible
+ * the timeout structure is provided
+ * by the caller
+ *
+ * @lock: the rt_mutex to be locked
+ * @timeout: timeout structure or NULL (no timeout)
+ *
+ * Returns:
+ * 0 on success
+ * -EINTR when interrupted by a signal
+ * -ETIMEDOUT when the timeout expired
+ */
+int
+rt_mutex_timed_lock(struct rt_mutex *lock, struct hrtimer_sleeper *timeout)
+{
+ int ret;
+
+ might_sleep();
+
+ mutex_acquire(&lock->dep_map, 0, 0, _RET_IP_);
+ ret = rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
+ RT_MUTEX_MIN_CHAINWALK,
+ rt_mutex_slowlock);
+ if (ret)
+ mutex_release(&lock->dep_map, 1, _RET_IP_);
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(rt_mutex_timed_lock);
+
+/**
+ * rt_mutex_trylock - try to lock a rt_mutex
+ *
+ * @lock: the rt_mutex to be locked
+ *
+ * This function can only be called in thread context. It's safe to
+ * call it from atomic regions, but not from hard interrupt or soft
+ * interrupt context.
+ *
+ * Returns 1 on success and 0 on contention
+ */
+int __sched rt_mutex_trylock(struct rt_mutex *lock)
+{
+ int ret;
+
+ if (WARN_ON_ONCE(in_irq() || in_nmi() || in_serving_softirq()))
+ return 0;
+
+ ret = rt_mutex_fasttrylock(lock, rt_mutex_slowtrylock);
+ if (ret)
+ mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(rt_mutex_trylock);
+
+/**
+ * rt_mutex_unlock - unlock a rt_mutex
+ *
+ * @lock: the rt_mutex to be unlocked
+ */
+void __sched rt_mutex_unlock(struct rt_mutex *lock)
+{
+ mutex_release(&lock->dep_map, 1, _RET_IP_);
+ rt_mutex_fastunlock(lock, rt_mutex_slowunlock);
+}
+EXPORT_SYMBOL_GPL(rt_mutex_unlock);
+
+/**
+ * Futex variant, that since futex variants do not use the fast-path, can be
+ * simple and will not need to retry.
+ */
+bool __sched __rt_mutex_futex_unlock(struct rt_mutex *lock,
+ struct wake_q_head *wake_q)
+{
+ lockdep_assert_held(&lock->wait_lock);
+
+ debug_rt_mutex_unlock(lock);
+
+ if (!rt_mutex_has_waiters(lock)) {
+ lock->owner = NULL;
+ return false; /* done */
+ }
+
+ /*
+ * We've already deboosted, mark_wakeup_next_waiter() will
+ * retain preempt_disabled when we drop the wait_lock, to
+ * avoid inversion prior to the wakeup. preempt_disable()
+ * therein pairs with rt_mutex_postunlock().
+ */
+ mark_wakeup_next_waiter(wake_q, lock);
+
+ return true; /* call postunlock() */
+}
+
+void __sched rt_mutex_futex_unlock(struct rt_mutex *lock)
+{
+ DEFINE_WAKE_Q(wake_q);
+ unsigned long flags;
+ bool postunlock;
+
+ raw_spin_lock_irqsave(&lock->wait_lock, flags);
+ postunlock = __rt_mutex_futex_unlock(lock, &wake_q);
+ raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
+
+ if (postunlock)
+ rt_mutex_postunlock(&wake_q);
+}
+
+/**
+ * rt_mutex_destroy - mark a 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.
+ */
+void rt_mutex_destroy(struct rt_mutex *lock)
+{
+ WARN_ON(rt_mutex_is_locked(lock));
+#ifdef CONFIG_DEBUG_RT_MUTEXES
+ lock->magic = NULL;
+#endif
+}
+EXPORT_SYMBOL_GPL(rt_mutex_destroy);
+
+/**
+ * __rt_mutex_init - initialize the rt lock
+ *
+ * @lock: the rt lock to be initialized
+ *
+ * Initialize the rt lock to unlocked state.
+ *
+ * Initializing of a locked rt lock is not allowed
+ */
+void __rt_mutex_init(struct rt_mutex *lock, const char *name,
+ struct lock_class_key *key)
+{
+ lock->owner = NULL;
+ raw_spin_lock_init(&lock->wait_lock);
+ lock->waiters = RB_ROOT_CACHED;
+
+ if (name && key)
+ debug_rt_mutex_init(lock, name, key);
+}
+EXPORT_SYMBOL_GPL(__rt_mutex_init);
+
+/**
+ * rt_mutex_init_proxy_locked - initialize and lock a rt_mutex on behalf of a
+ * proxy owner
+ *
+ * @lock: the rt_mutex to be locked
+ * @proxy_owner:the task to set as owner
+ *
+ * No locking. Caller has to do serializing itself
+ *
+ * Special API call for PI-futex support. This initializes the rtmutex and
+ * assigns it to @proxy_owner. Concurrent operations on the rtmutex are not
+ * possible at this point because the pi_state which contains the rtmutex
+ * is not yet visible to other tasks.
+ */
+void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
+ struct task_struct *proxy_owner)
+{
+ __rt_mutex_init(lock, NULL, NULL);
+ debug_rt_mutex_proxy_lock(lock, proxy_owner);
+ rt_mutex_set_owner(lock, proxy_owner);
+}
+
+/**
+ * rt_mutex_proxy_unlock - release a lock on behalf of owner
+ *
+ * @lock: the rt_mutex to be locked
+ *
+ * No locking. Caller has to do serializing itself
+ *
+ * Special API call for PI-futex support. This merrily cleans up the rtmutex
+ * (debugging) state. Concurrent operations on this rt_mutex are not
+ * possible because it belongs to the pi_state which is about to be freed
+ * and it is not longer visible to other tasks.
+ */
+void rt_mutex_proxy_unlock(struct rt_mutex *lock,
+ struct task_struct *proxy_owner)
+{
+ debug_rt_mutex_proxy_unlock(lock);
+ rt_mutex_set_owner(lock, NULL);
+}
+
+int __rt_mutex_start_proxy_lock(struct rt_mutex *lock,
+ struct rt_mutex_waiter *waiter,
+ struct task_struct *task)
+{
+ int ret;
+
+ if (try_to_take_rt_mutex(lock, task, NULL))
+ return 1;
+
+ /* We enforce deadlock detection for futexes */
+ ret = task_blocks_on_rt_mutex(lock, waiter, task,
+ RT_MUTEX_FULL_CHAINWALK);
+
+ if (ret && !rt_mutex_owner(lock)) {
+ /*
+ * Reset the return value. We might have
+ * returned with -EDEADLK and the owner
+ * released the lock while we were walking the
+ * pi chain. Let the waiter sort it out.
+ */
+ ret = 0;
+ }
+
+ if (unlikely(ret))
+ remove_waiter(lock, waiter);
+
+ debug_rt_mutex_print_deadlock(waiter);
+
+ return ret;
+}
+
+/**
+ * rt_mutex_start_proxy_lock() - Start lock acquisition for another task
+ * @lock: the rt_mutex to take
+ * @waiter: the pre-initialized rt_mutex_waiter
+ * @task: the task to prepare
+ *
+ * Returns:
+ * 0 - task blocked on lock
+ * 1 - acquired the lock for task, caller should wake it up
+ * <0 - error
+ *
+ * Special API call for FUTEX_REQUEUE_PI support.
+ */
+int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
+ struct rt_mutex_waiter *waiter,
+ struct task_struct *task)
+{
+ int ret;
+
+ raw_spin_lock_irq(&lock->wait_lock);
+ ret = __rt_mutex_start_proxy_lock(lock, waiter, task);
+ raw_spin_unlock_irq(&lock->wait_lock);
+
+ return ret;
+}
+
+/**
+ * rt_mutex_next_owner - return the next owner of the lock
+ *
+ * @lock: the rt lock query
+ *
+ * Returns the next owner of the lock or NULL
+ *
+ * Caller has to serialize against other accessors to the lock
+ * itself.
+ *
+ * Special API call for PI-futex support
+ */
+struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock)
+{
+ if (!rt_mutex_has_waiters(lock))
+ return NULL;
+
+ return rt_mutex_top_waiter(lock)->task;
+}
+
+/**
+ * rt_mutex_wait_proxy_lock() - Wait for lock acquisition
+ * @lock: the rt_mutex we were woken on
+ * @to: the timeout, null if none. hrtimer should already have
+ * been started.
+ * @waiter: the pre-initialized rt_mutex_waiter
+ *
+ * Wait for the the lock acquisition started on our behalf by
+ * rt_mutex_start_proxy_lock(). Upon failure, the caller must call
+ * rt_mutex_cleanup_proxy_lock().
+ *
+ * Returns:
+ * 0 - success
+ * <0 - error, one of -EINTR, -ETIMEDOUT
+ *
+ * Special API call for PI-futex support
+ */
+int rt_mutex_wait_proxy_lock(struct rt_mutex *lock,
+ struct hrtimer_sleeper *to,
+ struct rt_mutex_waiter *waiter)
+{
+ int ret;
+
+ raw_spin_lock_irq(&lock->wait_lock);
+ /* sleep on the mutex */
+ set_current_state(TASK_INTERRUPTIBLE);
+ ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter);
+ /*
+ * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
+ * have to fix that up.
+ */
+ fixup_rt_mutex_waiters(lock);
+ raw_spin_unlock_irq(&lock->wait_lock);
+
+ return ret;
+}
+
+/**
+ * rt_mutex_cleanup_proxy_lock() - Cleanup failed lock acquisition
+ * @lock: the rt_mutex we were woken on
+ * @waiter: the pre-initialized rt_mutex_waiter
+ *
+ * Attempt to clean up after a failed rt_mutex_wait_proxy_lock().
+ *
+ * Unless we acquired the lock; we're still enqueued on the wait-list and can
+ * in fact still be granted ownership until we're removed. Therefore we can
+ * find we are in fact the owner and must disregard the
+ * rt_mutex_wait_proxy_lock() failure.
+ *
+ * Returns:
+ * true - did the cleanup, we done.
+ * false - we acquired the lock after rt_mutex_wait_proxy_lock() returned,
+ * caller should disregards its return value.
+ *
+ * Special API call for PI-futex support
+ */
+bool rt_mutex_cleanup_proxy_lock(struct rt_mutex *lock,
+ struct rt_mutex_waiter *waiter)
+{
+ bool cleanup = false;
+
+ raw_spin_lock_irq(&lock->wait_lock);
+ /*
+ * Do an unconditional try-lock, this deals with the lock stealing
+ * state where __rt_mutex_futex_unlock() -> mark_wakeup_next_waiter()
+ * sets a NULL owner.
+ *
+ * We're not interested in the return value, because the subsequent
+ * test on rt_mutex_owner() will infer that. If the trylock succeeded,
+ * we will own the lock and it will have removed the waiter. If we
+ * failed the trylock, we're still not owner and we need to remove
+ * ourselves.
+ */
+ try_to_take_rt_mutex(lock, current, waiter);
+ /*
+ * Unless we're the owner; we're still enqueued on the wait_list.
+ * So check if we became owner, if not, take us off the wait_list.
+ */
+ if (rt_mutex_owner(lock) != current) {
+ remove_waiter(lock, waiter);
+ cleanup = true;
+ }
+ /*
+ * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
+ * have to fix that up.
+ */
+ fixup_rt_mutex_waiters(lock);
+
+ raw_spin_unlock_irq(&lock->wait_lock);
+
+ return cleanup;
+}