--- /dev/null
+/*
+ * 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.txt for details.
+ */
+#include <linux/spinlock.h>
+#include <linux/export.h>
+#include <linux/sched.h>
+#include <linux/sched/rt.h>
+#include <linux/sched/deadline.h>
+#include <linux/timer.h>
+#include <linux/ww_mutex.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)
+{
+ if (!rt_mutex_has_waiters(lock))
+ clear_rt_mutex_waiters(lock);
+}
+
+static int rt_mutex_real_waiter(struct rt_mutex_waiter *waiter)
+{
+ return waiter && waiter != PI_WAKEUP_INPROGRESS &&
+ waiter != PI_REQUEUE_INPROGRESS;
+}
+
+/*
+ * We can speed up the acquire/release, if the architecture
+ * supports cmpxchg and if there's no debugging state to be set up
+ */
+#if defined(__HAVE_ARCH_CMPXCHG) && !defined(CONFIG_DEBUG_RT_MUTEXES)
+# define rt_mutex_cmpxchg(l,c,n) (cmpxchg(&l->owner, c, n) == c)
+static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
+{
+ unsigned long owner, *p = (unsigned long *) &lock->owner;
+
+ do {
+ owner = *p;
+ } while (cmpxchg(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)
+ __releases(lock->wait_lock)
+{
+ struct task_struct *owner = rt_mutex_owner(lock);
+
+ clear_rt_mutex_waiters(lock);
+ raw_spin_unlock(&lock->wait_lock);
+ /*
+ * 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(lock, owner, NULL);
+}
+
+#else
+# define rt_mutex_cmpxchg(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)
+ __releases(lock->wait_lock)
+{
+ lock->owner = NULL;
+ raw_spin_unlock(&lock->wait_lock);
+ return true;
+}
+#endif
+
+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 (left->task->dl.deadline < right->task->dl.deadline);
+
+ return 0;
+}
+
+static void
+rt_mutex_enqueue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
+{
+ struct rb_node **link = &lock->waiters.rb_node;
+ struct rb_node *parent = NULL;
+ struct rt_mutex_waiter *entry;
+ int leftmost = 1;
+
+ 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 = 0;
+ }
+ }
+
+ if (leftmost)
+ lock->waiters_leftmost = &waiter->tree_entry;
+
+ rb_link_node(&waiter->tree_entry, parent, link);
+ rb_insert_color(&waiter->tree_entry, &lock->waiters);
+}
+
+static void
+rt_mutex_dequeue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
+{
+ if (RB_EMPTY_NODE(&waiter->tree_entry))
+ return;
+
+ if (lock->waiters_leftmost == &waiter->tree_entry)
+ lock->waiters_leftmost = rb_next(&waiter->tree_entry);
+
+ rb_erase(&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_node;
+ struct rb_node *parent = NULL;
+ struct rt_mutex_waiter *entry;
+ int leftmost = 1;
+
+ 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 = 0;
+ }
+ }
+
+ if (leftmost)
+ task->pi_waiters_leftmost = &waiter->pi_tree_entry;
+
+ rb_link_node(&waiter->pi_tree_entry, parent, link);
+ rb_insert_color(&waiter->pi_tree_entry, &task->pi_waiters);
+}
+
+static void
+rt_mutex_dequeue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
+{
+ if (RB_EMPTY_NODE(&waiter->pi_tree_entry))
+ return;
+
+ if (task->pi_waiters_leftmost == &waiter->pi_tree_entry)
+ task->pi_waiters_leftmost = rb_next(&waiter->pi_tree_entry);
+
+ rb_erase(&waiter->pi_tree_entry, &task->pi_waiters);
+ RB_CLEAR_NODE(&waiter->pi_tree_entry);
+}
+
+/*
+ * Calculate task priority from the waiter tree priority
+ *
+ * Return task->normal_prio when the waiter tree is empty or when
+ * the waiter is not allowed to do priority boosting
+ */
+int rt_mutex_getprio(struct task_struct *task)
+{
+ if (likely(!task_has_pi_waiters(task)))
+ return task->normal_prio;
+
+ return min(task_top_pi_waiter(task)->prio,
+ task->normal_prio);
+}
+
+struct task_struct *rt_mutex_get_top_task(struct task_struct *task)
+{
+ if (likely(!task_has_pi_waiters(task)))
+ return NULL;
+
+ return task_top_pi_waiter(task)->task;
+}
+
+/*
+ * Called by sched_setscheduler() to get the priority which will be
+ * effective after the change.
+ */
+int rt_mutex_get_effective_prio(struct task_struct *task, int newprio)
+{
+ if (!task_has_pi_waiters(task))
+ return newprio;
+
+ if (task_top_pi_waiter(task)->task->prio <= newprio)
+ return task_top_pi_waiter(task)->task->prio;
+ return newprio;
+}
+
+/*
+ * Adjust the priority of a task, after its pi_waiters got modified.
+ *
+ * This can be both boosting and unboosting. task->pi_lock must be held.
+ */
+static void __rt_mutex_adjust_prio(struct task_struct *task)
+{
+ int prio = rt_mutex_getprio(task);
+
+ if (task->prio != prio || dl_prio(prio))
+ rt_mutex_setprio(task, prio);
+}
+
+/*
+ * Adjust task priority (undo boosting). Called from the exit path of
+ * rt_mutex_slowunlock() and rt_mutex_slowlock().
+ *
+ * (Note: We do this outside of the protection of lock->wait_lock to
+ * allow the lock to be taken while or before we readjust the priority
+ * of task. We do not use the spin_xx_mutex() variants here as we are
+ * outside of the debug path.)
+ */
+void rt_mutex_adjust_prio(struct task_struct *task)
+{
+ unsigned long flags;
+
+ raw_spin_lock_irqsave(&task->pi_lock, flags);
+ __rt_mutex_adjust_prio(task);
+ raw_spin_unlock_irqrestore(&task->pi_lock, flags);
+}
+
+/*
+ * 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);
+}
+
+static void rt_mutex_wake_waiter(struct rt_mutex_waiter *waiter)
+{
+ if (waiter->savestate)
+ wake_up_lock_sleeper(waiter->task);
+ else
+ wake_up_process(waiter->task);
+}
+
+/*
+ * 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 rt_mutex_real_waiter(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;
+ unsigned long flags;
+ 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_irqsave(&task->pi_lock, flags);
+
+ /*
+ * [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 (!rt_mutex_real_waiter(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 (waiter->prio == task->prio) {
+ 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_irqrestore(&task->pi_lock, flags);
+ 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_irqrestore(&task->pi_lock, flags);
+ 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(&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_irqsave(&task->pi_lock, flags);
+
+ /*
+ * 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_irqrestore(&task->pi_lock, flags);
+ raw_spin_unlock(&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 list. */
+ rt_mutex_dequeue(lock, waiter);
+ waiter->prio = task->prio;
+ rt_mutex_enqueue(lock, waiter);
+
+ /* [8] Release the task */
+ raw_spin_unlock_irqrestore(&task->pi_lock, flags);
+ 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)) {
+ struct rt_mutex_waiter *lock_top_waiter;
+
+ /*
+ * 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.
+ */
+ lock_top_waiter = rt_mutex_top_waiter(lock);
+ if (prerequeue_top_waiter != lock_top_waiter)
+ rt_mutex_wake_waiter(lock_top_waiter);
+ raw_spin_unlock(&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_irqsave(&task->pi_lock, flags);
+
+ /* [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 list 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 list 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_irqrestore(&task->pi_lock, flags);
+ raw_spin_unlock(&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_irqrestore(&task->pi_lock, flags);
+ out_put_task:
+ put_task_struct(task);
+
+ return ret;
+}
+
+
+#define STEAL_NORMAL 0
+#define STEAL_LATERAL 1
+
+/*
+ * Note that RT tasks are excluded from lateral-steals to prevent the
+ * introduction of an unbounded latency
+ */
+static inline int lock_is_stealable(struct task_struct *task,
+ struct task_struct *pendowner, int mode)
+{
+ if (mode == STEAL_NORMAL || rt_task(task)) {
+ if (task->prio >= pendowner->prio)
+ return 0;
+ } else if (task->prio > pendowner->prio)
+ return 0;
+ return 1;
+}
+
+/*
+ * Try to take an rt-mutex
+ *
+ * Must be called with lock->wait_lock held.
+ *
+ * @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 list 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, int mode)
+{
+ unsigned long flags;
+
+ /*
+ * 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 list. 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)) {
+ /* XXX lock_is_stealable() ? */
+ return 0;
+ }
+
+ /*
+ * We can acquire the lock. Remove the waiter from the
+ * lock waiters list.
+ */
+ 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)) {
+ struct task_struct *pown = rt_mutex_top_waiter(lock)->task;
+
+ if (task != pown && !lock_is_stealable(task, pown, mode))
+ 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 list.
+ */
+ 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_irqsave(&task->pi_lock, flags);
+ 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 list.
+ */
+ if (rt_mutex_has_waiters(lock))
+ rt_mutex_enqueue_pi(task, rt_mutex_top_waiter(lock));
+ raw_spin_unlock_irqrestore(&task->pi_lock, flags);
+
+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);
+
+ rt_mutex_deadlock_account_lock(lock, task);
+
+ return 1;
+}
+
+#ifdef CONFIG_PREEMPT_RT_FULL
+/*
+ * preemptible spin_lock functions:
+ */
+static inline void rt_spin_lock_fastlock(struct rt_mutex *lock,
+ void (*slowfn)(struct rt_mutex *lock))
+{
+ might_sleep_no_state_check();
+
+ if (likely(rt_mutex_cmpxchg(lock, NULL, current)))
+ rt_mutex_deadlock_account_lock(lock, current);
+ else
+ slowfn(lock);
+}
+
+static inline void rt_spin_lock_fastunlock(struct rt_mutex *lock,
+ void (*slowfn)(struct rt_mutex *lock))
+{
+ if (likely(rt_mutex_cmpxchg(lock, current, NULL)))
+ rt_mutex_deadlock_account_unlock(current);
+ else
+ slowfn(lock);
+}
+#ifdef CONFIG_SMP
+/*
+ * Note that owner is a speculative pointer and dereferencing relies
+ * on rcu_read_lock() and the check against the lock owner.
+ */
+static int adaptive_wait(struct rt_mutex *lock,
+ struct task_struct *owner)
+{
+ int res = 0;
+
+ rcu_read_lock();
+ for (;;) {
+ if (owner != rt_mutex_owner(lock))
+ break;
+ /*
+ * Ensure that owner->on_cpu is dereferenced _after_
+ * checking the above to be valid.
+ */
+ barrier();
+ if (!owner->on_cpu) {
+ res = 1;
+ break;
+ }
+ cpu_relax();
+ }
+ rcu_read_unlock();
+ return res;
+}
+#else
+static int adaptive_wait(struct rt_mutex *lock,
+ struct task_struct *orig_owner)
+{
+ return 1;
+}
+#endif
+
+# define pi_lock(lock) raw_spin_lock_irq(lock)
+# define pi_unlock(lock) raw_spin_unlock_irq(lock)
+
+static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
+ struct rt_mutex_waiter *waiter,
+ struct task_struct *task,
+ enum rtmutex_chainwalk chwalk);
+/*
+ * Slow path lock function spin_lock style: this variant is very
+ * careful not to miss any non-lock wakeups.
+ *
+ * We store the current state under p->pi_lock in p->saved_state and
+ * the try_to_wake_up() code handles this accordingly.
+ */
+static void noinline __sched rt_spin_lock_slowlock(struct rt_mutex *lock)
+{
+ struct task_struct *lock_owner, *self = current;
+ struct rt_mutex_waiter waiter, *top_waiter;
+ int ret;
+
+ rt_mutex_init_waiter(&waiter, true);
+
+ raw_spin_lock(&lock->wait_lock);
+
+ if (__try_to_take_rt_mutex(lock, self, NULL, STEAL_LATERAL)) {
+ raw_spin_unlock(&lock->wait_lock);
+ return;
+ }
+
+ BUG_ON(rt_mutex_owner(lock) == self);
+
+ /*
+ * We save whatever state the task is in and we'll restore it
+ * after acquiring the lock taking real wakeups into account
+ * as well. We are serialized via pi_lock against wakeups. See
+ * try_to_wake_up().
+ */
+ pi_lock(&self->pi_lock);
+ self->saved_state = self->state;
+ __set_current_state_no_track(TASK_UNINTERRUPTIBLE);
+ pi_unlock(&self->pi_lock);
+
+ ret = task_blocks_on_rt_mutex(lock, &waiter, self, 0);
+ BUG_ON(ret);
+
+ for (;;) {
+ /* Try to acquire the lock again. */
+ if (__try_to_take_rt_mutex(lock, self, &waiter, STEAL_LATERAL))
+ break;
+
+ top_waiter = rt_mutex_top_waiter(lock);
+ lock_owner = rt_mutex_owner(lock);
+
+ raw_spin_unlock(&lock->wait_lock);
+
+ debug_rt_mutex_print_deadlock(&waiter);
+
+ if (top_waiter != &waiter || adaptive_wait(lock, lock_owner))
+ schedule_rt_mutex(lock);
+
+ raw_spin_lock(&lock->wait_lock);
+
+ pi_lock(&self->pi_lock);
+ __set_current_state_no_track(TASK_UNINTERRUPTIBLE);
+ pi_unlock(&self->pi_lock);
+ }
+
+ /*
+ * Restore the task state to current->saved_state. We set it
+ * to the original state above and the try_to_wake_up() code
+ * has possibly updated it when a real (non-rtmutex) wakeup
+ * happened while we were blocked. Clear saved_state so
+ * try_to_wakeup() does not get confused.
+ */
+ pi_lock(&self->pi_lock);
+ __set_current_state_no_track(self->saved_state);
+ self->saved_state = TASK_RUNNING;
+ pi_unlock(&self->pi_lock);
+
+ /*
+ * try_to_take_rt_mutex() sets the waiter bit
+ * unconditionally. We might have to fix that up:
+ */
+ fixup_rt_mutex_waiters(lock);
+
+ BUG_ON(rt_mutex_has_waiters(lock) && &waiter == rt_mutex_top_waiter(lock));
+ BUG_ON(!RB_EMPTY_NODE(&waiter.tree_entry));
+
+ raw_spin_unlock(&lock->wait_lock);
+
+ debug_rt_mutex_free_waiter(&waiter);
+}
+
+static void wakeup_next_waiter(struct rt_mutex *lock);
+/*
+ * Slow path to release a rt_mutex spin_lock style
+ */
+static void noinline __sched rt_spin_lock_slowunlock(struct rt_mutex *lock)
+{
+ raw_spin_lock(&lock->wait_lock);
+
+ debug_rt_mutex_unlock(lock);
+
+ rt_mutex_deadlock_account_unlock(current);
+
+ if (!rt_mutex_has_waiters(lock)) {
+ lock->owner = NULL;
+ raw_spin_unlock(&lock->wait_lock);
+ return;
+ }
+
+ wakeup_next_waiter(lock);
+
+ raw_spin_unlock(&lock->wait_lock);
+
+ /* Undo pi boosting.when necessary */
+ rt_mutex_adjust_prio(current);
+}
+
+void __lockfunc rt_spin_lock(spinlock_t *lock)
+{
+ rt_spin_lock_fastlock(&lock->lock, rt_spin_lock_slowlock);
+ spin_acquire(&lock->dep_map, 0, 0, _RET_IP_);
+}
+EXPORT_SYMBOL(rt_spin_lock);
+
+void __lockfunc __rt_spin_lock(struct rt_mutex *lock)
+{
+ rt_spin_lock_fastlock(lock, rt_spin_lock_slowlock);
+}
+EXPORT_SYMBOL(__rt_spin_lock);
+
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+void __lockfunc rt_spin_lock_nested(spinlock_t *lock, int subclass)
+{
+ rt_spin_lock_fastlock(&lock->lock, rt_spin_lock_slowlock);
+ spin_acquire(&lock->dep_map, subclass, 0, _RET_IP_);
+}
+EXPORT_SYMBOL(rt_spin_lock_nested);
+#endif
+
+void __lockfunc rt_spin_unlock(spinlock_t *lock)
+{
+ /* NOTE: we always pass in '1' for nested, for simplicity */
+ spin_release(&lock->dep_map, 1, _RET_IP_);
+ rt_spin_lock_fastunlock(&lock->lock, rt_spin_lock_slowunlock);
+}
+EXPORT_SYMBOL(rt_spin_unlock);
+
+void __lockfunc __rt_spin_unlock(struct rt_mutex *lock)
+{
+ rt_spin_lock_fastunlock(lock, rt_spin_lock_slowunlock);
+}
+EXPORT_SYMBOL(__rt_spin_unlock);
+
+/*
+ * Wait for the lock to get unlocked: instead of polling for an unlock
+ * (like raw spinlocks do), we lock and unlock, to force the kernel to
+ * schedule if there's contention:
+ */
+void __lockfunc rt_spin_unlock_wait(spinlock_t *lock)
+{
+ spin_lock(lock);
+ spin_unlock(lock);
+}
+EXPORT_SYMBOL(rt_spin_unlock_wait);
+
+int __lockfunc __rt_spin_trylock(struct rt_mutex *lock)
+{
+ return rt_mutex_trylock(lock);
+}
+
+int __lockfunc rt_spin_trylock(spinlock_t *lock)
+{
+ int ret = rt_mutex_trylock(&lock->lock);
+
+ if (ret)
+ spin_acquire(&lock->dep_map, 0, 1, _RET_IP_);
+ return ret;
+}
+EXPORT_SYMBOL(rt_spin_trylock);
+
+int __lockfunc rt_spin_trylock_bh(spinlock_t *lock)
+{
+ int ret;
+
+ local_bh_disable();
+ ret = rt_mutex_trylock(&lock->lock);
+ if (ret) {
+ migrate_disable();
+ spin_acquire(&lock->dep_map, 0, 1, _RET_IP_);
+ } else
+ local_bh_enable();
+ return ret;
+}
+EXPORT_SYMBOL(rt_spin_trylock_bh);
+
+int __lockfunc rt_spin_trylock_irqsave(spinlock_t *lock, unsigned long *flags)
+{
+ int ret;
+
+ *flags = 0;
+ ret = rt_mutex_trylock(&lock->lock);
+ if (ret) {
+ migrate_disable();
+ spin_acquire(&lock->dep_map, 0, 1, _RET_IP_);
+ }
+ return ret;
+}
+EXPORT_SYMBOL(rt_spin_trylock_irqsave);
+
+int atomic_dec_and_spin_lock(atomic_t *atomic, spinlock_t *lock)
+{
+ /* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */
+ if (atomic_add_unless(atomic, -1, 1))
+ return 0;
+ migrate_disable();
+ rt_spin_lock(lock);
+ if (atomic_dec_and_test(atomic))
+ return 1;
+ rt_spin_unlock(lock);
+ migrate_enable();
+ return 0;
+}
+EXPORT_SYMBOL(atomic_dec_and_spin_lock);
+
+ void
+__rt_spin_lock_init(spinlock_t *lock, char *name, struct lock_class_key *key)
+{
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+ /*
+ * Make sure we are not reinitializing a held lock:
+ */
+ debug_check_no_locks_freed((void *)lock, sizeof(*lock));
+ lockdep_init_map(&lock->dep_map, name, key, 0);
+#endif
+}
+EXPORT_SYMBOL(__rt_spin_lock_init);
+
+#endif /* PREEMPT_RT_FULL */
+
+#ifdef CONFIG_PREEMPT_RT_FULL
+ static inline int __sched
+__mutex_lock_check_stamp(struct rt_mutex *lock, struct ww_acquire_ctx *ctx)
+{
+ struct ww_mutex *ww = container_of(lock, struct ww_mutex, base.lock);
+ struct ww_acquire_ctx *hold_ctx = ACCESS_ONCE(ww->ctx);
+
+ if (!hold_ctx)
+ return 0;
+
+ if (unlikely(ctx == hold_ctx))
+ return -EALREADY;
+
+ if (ctx->stamp - hold_ctx->stamp <= LONG_MAX &&
+ (ctx->stamp != hold_ctx->stamp || ctx > hold_ctx)) {
+#ifdef CONFIG_DEBUG_MUTEXES
+ DEBUG_LOCKS_WARN_ON(ctx->contending_lock);
+ ctx->contending_lock = ww;
+#endif
+ return -EDEADLK;
+ }
+
+ return 0;
+}
+#else
+ static inline int __sched
+__mutex_lock_check_stamp(struct rt_mutex *lock, struct ww_acquire_ctx *ctx)
+{
+ BUG();
+ return 0;
+}
+
+#endif
+
+static inline int
+try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task,
+ struct rt_mutex_waiter *waiter)
+{
+ return __try_to_take_rt_mutex(lock, task, waiter, STEAL_NORMAL);
+}
+
+/*
+ * Task blocks on lock.
+ *
+ * Prepare waiter and propagate pi chain
+ *
+ * This must be called with lock->wait_lock held.
+ */
+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;
+ unsigned long flags;
+
+ /*
+ * 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_irqsave(&task->pi_lock, flags);
+
+ /*
+ * In the case of futex requeue PI, this will be a proxy
+ * lock. The task will wake unaware that it is enqueueed on
+ * this lock. Avoid blocking on two locks and corrupting
+ * pi_blocked_on via the PI_WAKEUP_INPROGRESS
+ * flag. futex_wait_requeue_pi() sets this when it wakes up
+ * before requeue (due to a signal or timeout). Do not enqueue
+ * the task if PI_WAKEUP_INPROGRESS is set.
+ */
+ if (task != current && task->pi_blocked_on == PI_WAKEUP_INPROGRESS) {
+ raw_spin_unlock_irqrestore(&task->pi_lock, flags);
+ return -EAGAIN;
+ }
+
+ BUG_ON(rt_mutex_real_waiter(task->pi_blocked_on));
+
+ __rt_mutex_adjust_prio(task);
+ waiter->task = task;
+ waiter->lock = lock;
+ waiter->prio = task->prio;
+
+ /* 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_irqrestore(&task->pi_lock, flags);
+
+ if (!owner)
+ return 0;
+
+ raw_spin_lock_irqsave(&owner->pi_lock, flags);
+ 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 (rt_mutex_real_waiter(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_irqrestore(&owner->pi_lock, flags);
+ /*
+ * 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(&lock->wait_lock);
+
+ res = rt_mutex_adjust_prio_chain(owner, chwalk, lock,
+ next_lock, waiter, task);
+
+ raw_spin_lock(&lock->wait_lock);
+
+ return res;
+}
+
+/*
+ * Wake up the next waiter on the lock.
+ *
+ * Remove the top waiter from the current tasks pi waiter list,
+ * wake it up and return whether the current task needs to undo
+ * a potential priority boosting.
+ *
+ * Called with lock->wait_lock held.
+ */
+static void wakeup_next_waiter(struct rt_mutex *lock)
+{
+ struct rt_mutex_waiter *waiter;
+ unsigned long flags;
+
+ raw_spin_lock_irqsave(¤t->pi_lock, flags);
+
+ waiter = rt_mutex_top_waiter(lock);
+
+ /*
+ * Remove it from current->pi_waiters. We do not adjust a
+ * possible priority boost right now. We execute wakeup in the
+ * boosted mode and go back to normal after releasing
+ * lock->wait_lock.
+ */
+ rt_mutex_dequeue_pi(current, waiter);
+
+ /*
+ * 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;
+
+ raw_spin_unlock_irqrestore(¤t->pi_lock, flags);
+
+ /*
+ * It's safe to dereference waiter as it cannot go away as
+ * long as we hold lock->wait_lock. The waiter task needs to
+ * acquire it in order to dequeue the waiter.
+ */
+ rt_mutex_wake_waiter(waiter);
+}
+
+/*
+ * Remove a waiter from a lock and give up
+ *
+ * Must be called with lock->wait_lock held and
+ * 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 = NULL;
+ unsigned long flags;
+
+ raw_spin_lock_irqsave(¤t->pi_lock, flags);
+ rt_mutex_dequeue(lock, waiter);
+ current->pi_blocked_on = NULL;
+ raw_spin_unlock_irqrestore(¤t->pi_lock, flags);
+
+ /*
+ * 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_irqsave(&owner->pi_lock, flags);
+
+ 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 */
+ if (rt_mutex_real_waiter(owner->pi_blocked_on))
+ next_lock = task_blocked_on_lock(owner);
+
+ raw_spin_unlock_irqrestore(&owner->pi_lock, flags);
+
+ /*
+ * 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(&lock->wait_lock);
+
+ rt_mutex_adjust_prio_chain(owner, RT_MUTEX_MIN_CHAINWALK, lock,
+ next_lock, NULL, current);
+
+ raw_spin_lock(&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 (!rt_mutex_real_waiter(waiter) || (waiter->prio == task->prio &&
+ !dl_prio(task->prio))) {
+ raw_spin_unlock_irqrestore(&task->pi_lock, flags);
+ return;
+ }
+ next_lock = waiter->lock;
+
+ /* gets dropped in rt_mutex_adjust_prio_chain()! */
+ get_task_struct(task);
+
+ raw_spin_unlock_irqrestore(&task->pi_lock, flags);
+ rt_mutex_adjust_prio_chain(task, RT_MUTEX_MIN_CHAINWALK, NULL,
+ next_lock, NULL, task);
+}
+
+/**
+ * __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
+ *
+ * lock->wait_lock must be held by the caller.
+ */
+static int __sched
+__rt_mutex_slowlock(struct rt_mutex *lock, int state,
+ struct hrtimer_sleeper *timeout,
+ struct rt_mutex_waiter *waiter,
+ struct ww_acquire_ctx *ww_ctx)
+{
+ 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 (unlikely(state == TASK_INTERRUPTIBLE)) {
+ /* Signal pending? */
+ if (signal_pending(current))
+ ret = -EINTR;
+ if (timeout && !timeout->task)
+ ret = -ETIMEDOUT;
+ if (ret)
+ break;
+ }
+
+ if (ww_ctx && ww_ctx->acquired > 0) {
+ ret = __mutex_lock_check_stamp(lock, ww_ctx);
+ if (ret)
+ break;
+ }
+
+ raw_spin_unlock(&lock->wait_lock);
+
+ debug_rt_mutex_print_deadlock(waiter);
+
+ schedule_rt_mutex(lock);
+
+ raw_spin_lock(&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();
+ }
+}
+
+static __always_inline void ww_mutex_lock_acquired(struct ww_mutex *ww,
+ struct ww_acquire_ctx *ww_ctx)
+{
+#ifdef CONFIG_DEBUG_MUTEXES
+ /*
+ * If this WARN_ON triggers, you used ww_mutex_lock to acquire,
+ * but released with a normal mutex_unlock in this call.
+ *
+ * This should never happen, always use ww_mutex_unlock.
+ */
+ DEBUG_LOCKS_WARN_ON(ww->ctx);
+
+ /*
+ * Not quite done after calling ww_acquire_done() ?
+ */
+ DEBUG_LOCKS_WARN_ON(ww_ctx->done_acquire);
+
+ if (ww_ctx->contending_lock) {
+ /*
+ * After -EDEADLK you tried to
+ * acquire a different ww_mutex? Bad!
+ */
+ DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock != ww);
+
+ /*
+ * You called ww_mutex_lock after receiving -EDEADLK,
+ * but 'forgot' to unlock everything else first?
+ */
+ DEBUG_LOCKS_WARN_ON(ww_ctx->acquired > 0);
+ ww_ctx->contending_lock = NULL;
+ }
+
+ /*
+ * Naughty, using a different class will lead to undefined behavior!
+ */
+ DEBUG_LOCKS_WARN_ON(ww_ctx->ww_class != ww->ww_class);
+#endif
+ ww_ctx->acquired++;
+}
+
+#ifdef CONFIG_PREEMPT_RT_FULL
+static void ww_mutex_account_lock(struct rt_mutex *lock,
+ struct ww_acquire_ctx *ww_ctx)
+{
+ struct ww_mutex *ww = container_of(lock, struct ww_mutex, base.lock);
+ struct rt_mutex_waiter *waiter, *n;
+
+ /*
+ * This branch gets optimized out for the common case,
+ * and is only important for ww_mutex_lock.
+ */
+ ww_mutex_lock_acquired(ww, ww_ctx);
+ ww->ctx = ww_ctx;
+
+ /*
+ * Give any possible sleeping processes the chance to wake up,
+ * so they can recheck if they have to back off.
+ */
+ rbtree_postorder_for_each_entry_safe(waiter, n, &lock->waiters,
+ tree_entry) {
+ /* XXX debug rt mutex waiter wakeup */
+
+ BUG_ON(waiter->lock != lock);
+ rt_mutex_wake_waiter(waiter);
+ }
+}
+
+#else
+
+static void ww_mutex_account_lock(struct rt_mutex *lock,
+ struct ww_acquire_ctx *ww_ctx)
+{
+ BUG();
+}
+#endif
+
+/*
+ * 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 ww_acquire_ctx *ww_ctx)
+{
+ struct rt_mutex_waiter waiter;
+ int ret = 0;
+
+ rt_mutex_init_waiter(&waiter, false);
+
+ raw_spin_lock(&lock->wait_lock);
+
+ /* Try to acquire the lock again: */
+ if (try_to_take_rt_mutex(lock, current, NULL)) {
+ if (ww_ctx)
+ ww_mutex_account_lock(lock, ww_ctx);
+ raw_spin_unlock(&lock->wait_lock);
+ return 0;
+ }
+
+ set_current_state(state);
+
+ /* Setup the timer, when timeout != NULL */
+ if (unlikely(timeout)) {
+ hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
+ if (!hrtimer_active(&timeout->timer))
+ timeout->task = NULL;
+ }
+
+ 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,
+ ww_ctx);
+ else if (ww_ctx) {
+ /* ww_mutex received EDEADLK, let it become EALREADY */
+ ret = __mutex_lock_check_stamp(lock, ww_ctx);
+ BUG_ON(!ret);
+ }
+
+ if (unlikely(ret)) {
+ __set_current_state(TASK_RUNNING);
+ if (rt_mutex_has_waiters(lock))
+ remove_waiter(lock, &waiter);
+ /* ww_mutex want to report EDEADLK/EALREADY, let them */
+ if (!ww_ctx)
+ rt_mutex_handle_deadlock(ret, chwalk, &waiter);
+ } else if (ww_ctx) {
+ ww_mutex_account_lock(lock, ww_ctx);
+ }
+
+ /*
+ * 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(&lock->wait_lock);
+
+ /* Remove pending timer: */
+ if (unlikely(timeout))
+ hrtimer_cancel(&timeout->timer);
+
+ debug_rt_mutex_free_waiter(&waiter);
+
+ return ret;
+}
+
+/*
+ * Slow path try-lock function:
+ */
+static inline int rt_mutex_slowtrylock(struct rt_mutex *lock)
+{
+ 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.
+ */
+ raw_spin_lock(&lock->wait_lock);
+
+ 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);
+
+ raw_spin_unlock(&lock->wait_lock);
+
+ return ret;
+}
+
+/*
+ * Slow path to release a rt-mutex:
+ */
+static bool __sched
+rt_mutex_slowunlock(struct rt_mutex *lock)
+{
+ raw_spin_lock(&lock->wait_lock);
+
+ debug_rt_mutex_unlock(lock);
+
+ rt_mutex_deadlock_account_unlock(current);
+
+ /*
+ * 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) == true)
+ return false;
+ /* Relock the rtmutex and try again */
+ raw_spin_lock(&lock->wait_lock);
+ }
+
+ /*
+ * The wakeup next waiter path does not suffer from the above
+ * race. See the comments there.
+ */
+ wakeup_next_waiter(lock);
+
+ raw_spin_unlock(&lock->wait_lock);
+
+ return true;
+}
+
+/*
+ * 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,
+ struct ww_acquire_ctx *ww_ctx,
+ int (*slowfn)(struct rt_mutex *lock, int state,
+ struct hrtimer_sleeper *timeout,
+ enum rtmutex_chainwalk chwalk,
+ struct ww_acquire_ctx *ww_ctx))
+{
+ if (likely(rt_mutex_cmpxchg(lock, NULL, current))) {
+ rt_mutex_deadlock_account_lock(lock, current);
+ return 0;
+ } else
+ return slowfn(lock, state, NULL, RT_MUTEX_MIN_CHAINWALK,
+ ww_ctx);
+}
+
+static inline int
+rt_mutex_timed_fastlock(struct rt_mutex *lock, int state,
+ struct hrtimer_sleeper *timeout,
+ enum rtmutex_chainwalk chwalk,
+ struct ww_acquire_ctx *ww_ctx,
+ int (*slowfn)(struct rt_mutex *lock, int state,
+ struct hrtimer_sleeper *timeout,
+ enum rtmutex_chainwalk chwalk,
+ struct ww_acquire_ctx *ww_ctx))
+{
+ if (chwalk == RT_MUTEX_MIN_CHAINWALK &&
+ likely(rt_mutex_cmpxchg(lock, NULL, current))) {
+ rt_mutex_deadlock_account_lock(lock, current);
+ return 0;
+ } else
+ return slowfn(lock, state, timeout, chwalk, ww_ctx);
+}
+
+static inline int
+rt_mutex_fasttrylock(struct rt_mutex *lock,
+ int (*slowfn)(struct rt_mutex *lock))
+{
+ if (likely(rt_mutex_cmpxchg(lock, NULL, current))) {
+ rt_mutex_deadlock_account_lock(lock, current);
+ return 1;
+ }
+ return slowfn(lock);
+}
+
+static inline void
+rt_mutex_fastunlock(struct rt_mutex *lock,
+ bool (*slowfn)(struct rt_mutex *lock))
+{
+ if (likely(rt_mutex_cmpxchg(lock, current, NULL))) {
+ rt_mutex_deadlock_account_unlock(current);
+ } else if (slowfn(lock)) {
+ /* Undo pi boosting if necessary: */
+ rt_mutex_adjust_prio(current);
+ }
+}
+
+/**
+ * rt_mutex_lock - lock a rt_mutex
+ *
+ * @lock: the rt_mutex to be locked
+ */
+void __sched rt_mutex_lock(struct rt_mutex *lock)
+{
+ might_sleep();
+
+ rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, NULL, rt_mutex_slowlock);
+}
+EXPORT_SYMBOL_GPL(rt_mutex_lock);
+
+/**
+ * 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)
+{
+ might_sleep();
+
+ return rt_mutex_fastlock(lock, TASK_INTERRUPTIBLE, NULL, rt_mutex_slowlock);
+}
+EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible);
+
+/*
+ * Futex variant with full deadlock detection.
+ */
+int rt_mutex_timed_futex_lock(struct rt_mutex *lock,
+ struct hrtimer_sleeper *timeout)
+{
+ might_sleep();
+
+ return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
+ RT_MUTEX_FULL_CHAINWALK, NULL,
+ rt_mutex_slowlock);
+}
+
+/**
+ * rt_mutex_lock_killable - lock a rt_mutex killable
+ *
+ * @lock: the rt_mutex to be locked
+ * @detect_deadlock: deadlock detection on/off
+ *
+ * Returns:
+ * 0 on success
+ * -EINTR when interrupted by a signal
+ * -EDEADLK when the lock would deadlock (when deadlock detection is on)
+ */
+int __sched rt_mutex_lock_killable(struct rt_mutex *lock)
+{
+ might_sleep();
+
+ return rt_mutex_fastlock(lock, TASK_KILLABLE, NULL, rt_mutex_slowlock);
+}
+EXPORT_SYMBOL_GPL(rt_mutex_lock_killable);
+
+/**
+ * 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)
+{
+ might_sleep();
+
+ return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
+ RT_MUTEX_MIN_CHAINWALK,
+ NULL,
+ rt_mutex_slowlock);
+}
+EXPORT_SYMBOL_GPL(rt_mutex_timed_lock);
+
+/**
+ * rt_mutex_trylock - try to lock a rt_mutex
+ *
+ * @lock: the rt_mutex to be locked
+ *
+ * Returns 1 on success and 0 on contention
+ */
+int __sched rt_mutex_trylock(struct rt_mutex *lock)
+{
+ return rt_mutex_fasttrylock(lock, rt_mutex_slowtrylock);
+}
+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)
+{
+ rt_mutex_fastunlock(lock, rt_mutex_slowunlock);
+}
+EXPORT_SYMBOL_GPL(rt_mutex_unlock);
+
+/**
+ * rt_mutex_futex_unlock - Futex variant of rt_mutex_unlock
+ * @lock: the rt_mutex to be unlocked
+ *
+ * Returns: true/false indicating whether priority adjustment is
+ * required or not.
+ */
+bool __sched rt_mutex_futex_unlock(struct rt_mutex *lock)
+{
+ if (likely(rt_mutex_cmpxchg(lock, current, NULL))) {
+ rt_mutex_deadlock_account_unlock(current);
+ return false;
+ }
+ return rt_mutex_slowunlock(lock);
+}
+
+/**
+ * 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)
+{
+ lock->owner = NULL;
+ lock->waiters = RB_ROOT;
+ lock->waiters_leftmost = NULL;
+
+ debug_rt_mutex_init(lock, name);
+}
+EXPORT_SYMBOL(__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
+ */
+void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
+ struct task_struct *proxy_owner)
+{
+ rt_mutex_init(lock);
+ debug_rt_mutex_proxy_lock(lock, proxy_owner);
+ rt_mutex_set_owner(lock, proxy_owner);
+ rt_mutex_deadlock_account_lock(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
+ */
+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);
+ rt_mutex_deadlock_account_unlock(proxy_owner);
+}
+
+/**
+ * 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(&lock->wait_lock);
+
+ if (try_to_take_rt_mutex(lock, task, NULL)) {
+ raw_spin_unlock(&lock->wait_lock);
+ return 1;
+ }
+
+#ifdef CONFIG_PREEMPT_RT_FULL
+ /*
+ * In PREEMPT_RT there's an added race.
+ * If the task, that we are about to requeue, times out,
+ * it can set the PI_WAKEUP_INPROGRESS. This tells the requeue
+ * to skip this task. But right after the task sets
+ * its pi_blocked_on to PI_WAKEUP_INPROGRESS it can then
+ * block on the spin_lock(&hb->lock), which in RT is an rtmutex.
+ * This will replace the PI_WAKEUP_INPROGRESS with the actual
+ * lock that it blocks on. We *must not* place this task
+ * on this proxy lock in that case.
+ *
+ * To prevent this race, we first take the task's pi_lock
+ * and check if it has updated its pi_blocked_on. If it has,
+ * we assume that it woke up and we return -EAGAIN.
+ * Otherwise, we set the task's pi_blocked_on to
+ * PI_REQUEUE_INPROGRESS, so that if the task is waking up
+ * it will know that we are in the process of requeuing it.
+ */
+ raw_spin_lock_irq(&task->pi_lock);
+ if (task->pi_blocked_on) {
+ raw_spin_unlock_irq(&task->pi_lock);
+ raw_spin_unlock(&lock->wait_lock);
+ return -EAGAIN;
+ }
+ task->pi_blocked_on = PI_REQUEUE_INPROGRESS;
+ raw_spin_unlock_irq(&task->pi_lock);
+#endif
+
+ /* 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);
+
+ raw_spin_unlock(&lock->wait_lock);
+
+ debug_rt_mutex_print_deadlock(waiter);
+
+ 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_finish_proxy_lock() - Complete 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
+ *
+ * Complete the lock acquisition started our behalf by another thread.
+ *
+ * Returns:
+ * 0 - success
+ * <0 - error, one of -EINTR, -ETIMEDOUT
+ *
+ * Special API call for PI-futex requeue support
+ */
+int rt_mutex_finish_proxy_lock(struct rt_mutex *lock,
+ struct hrtimer_sleeper *to,
+ struct rt_mutex_waiter *waiter)
+{
+ int ret;
+
+ raw_spin_lock(&lock->wait_lock);
+
+ set_current_state(TASK_INTERRUPTIBLE);
+
+ /* sleep on the mutex */
+ ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter, NULL);
+
+ if (unlikely(ret))
+ remove_waiter(lock, 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(&lock->wait_lock);
+
+ return ret;
+}
+
+static inline int
+ww_mutex_deadlock_injection(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
+{
+#ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
+ unsigned tmp;
+
+ if (ctx->deadlock_inject_countdown-- == 0) {
+ tmp = ctx->deadlock_inject_interval;
+ if (tmp > UINT_MAX/4)
+ tmp = UINT_MAX;
+ else
+ tmp = tmp*2 + tmp + tmp/2;
+
+ ctx->deadlock_inject_interval = tmp;
+ ctx->deadlock_inject_countdown = tmp;
+ ctx->contending_lock = lock;
+
+ ww_mutex_unlock(lock);
+
+ return -EDEADLK;
+ }
+#endif
+
+ return 0;
+}
+
+#ifdef CONFIG_PREEMPT_RT_FULL
+int __sched
+__ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ww_ctx)
+{
+ int ret;
+
+ might_sleep();
+
+ mutex_acquire_nest(&lock->base.dep_map, 0, 0, &ww_ctx->dep_map, _RET_IP_);
+ ret = rt_mutex_slowlock(&lock->base.lock, TASK_INTERRUPTIBLE, NULL, 0, ww_ctx);
+ if (ret)
+ mutex_release(&lock->base.dep_map, 1, _RET_IP_);
+ else if (!ret && ww_ctx->acquired > 1)
+ return ww_mutex_deadlock_injection(lock, ww_ctx);
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(__ww_mutex_lock_interruptible);
+
+int __sched
+__ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ww_ctx)
+{
+ int ret;
+
+ might_sleep();
+
+ mutex_acquire_nest(&lock->base.dep_map, 0, 0, &ww_ctx->dep_map, _RET_IP_);
+ ret = rt_mutex_slowlock(&lock->base.lock, TASK_UNINTERRUPTIBLE, NULL, 0, ww_ctx);
+ if (ret)
+ mutex_release(&lock->base.dep_map, 1, _RET_IP_);
+ else if (!ret && ww_ctx->acquired > 1)
+ return ww_mutex_deadlock_injection(lock, ww_ctx);
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(__ww_mutex_lock);
+
+void __sched ww_mutex_unlock(struct ww_mutex *lock)
+{
+ int nest = !!lock->ctx;
+
+ /*
+ * The unlocking fastpath is the 0->1 transition from 'locked'
+ * into 'unlocked' state:
+ */
+ if (nest) {
+#ifdef CONFIG_DEBUG_MUTEXES
+ DEBUG_LOCKS_WARN_ON(!lock->ctx->acquired);
+#endif
+ if (lock->ctx->acquired > 0)
+ lock->ctx->acquired--;
+ lock->ctx = NULL;
+ }
+
+ mutex_release(&lock->base.dep_map, nest, _RET_IP_);
+ rt_mutex_unlock(&lock->base.lock);
+}
+EXPORT_SYMBOL(ww_mutex_unlock);
+#endif
Code Review / kvmfornfv.git / blobdiff