// SPDX-License-Identifier: GPL-2.0-only
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/*
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* RT-Mutexes: simple blocking mutual exclusion locks with PI support
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*
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* started by Ingo Molnar and Thomas Gleixner.
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*
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* Copyright (C) 2004-2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
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* Copyright (C) 2005-2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
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* Copyright (C) 2005 Kihon Technologies Inc., Steven Rostedt
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* Copyright (C) 2006 Esben Nielsen
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* Adaptive Spinlocks:
|
* Copyright (C) 2008 Novell, Inc., Gregory Haskins, Sven Dietrich,
|
* and Peter Morreale,
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* Adaptive Spinlocks simplification:
|
* Copyright (C) 2008 Red Hat, Inc., Steven Rostedt <srostedt@redhat.com>
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*
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* See Documentation/locking/rt-mutex-design.rst for details.
|
*/
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#include <linux/spinlock.h>
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#include <linux/export.h>
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#include <linux/sched/signal.h>
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#include <linux/sched/rt.h>
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#include <linux/sched/deadline.h>
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#include <linux/sched/wake_q.h>
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#include <linux/sched/debug.h>
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#include <linux/timer.h>
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#include <trace/hooks/dtask.h>
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#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.
|
*
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* owner bit0
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* NULL 0 lock is free (fast acquire possible)
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* NULL 1 lock is free and has waiters and the top waiter
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* 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.
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*
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* (*) 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,
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* 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.
|
*
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* (**) 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.
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* To prevent a cmpxchg of the owner releasing the lock, we need to
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* set this bit before looking at the lock.
|
*/
|
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static void
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rt_mutex_set_owner(struct rt_mutex *lock, struct task_struct *owner)
|
{
|
unsigned long val = (unsigned long)owner;
|
|
if (rt_mutex_has_waiters(lock))
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val |= RT_MUTEX_HAS_WAITERS;
|
|
WRITE_ONCE(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);
|
}
|
|
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 there's no debugging state to be
|
* set up.
|
*/
|
#ifndef CONFIG_DEBUG_RT_MUTEXES
|
# 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_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, .task = (p) }
|
|
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;
|
}
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|
#define STEAL_NORMAL 0
|
#define STEAL_LATERAL 1
|
|
static inline int
|
rt_mutex_steal(struct rt_mutex *lock, struct rt_mutex_waiter *waiter, int mode)
|
{
|
struct rt_mutex_waiter *top_waiter = rt_mutex_top_waiter(lock);
|
|
if (waiter == top_waiter || rt_mutex_waiter_less(waiter, top_waiter))
|
return 1;
|
|
/*
|
* Note that RT tasks are excluded from lateral-steals
|
* to prevent the introduction of an unbounded latency.
|
*/
|
if (mode == STEAL_NORMAL || rt_task(waiter->task))
|
return 0;
|
|
return rt_mutex_waiter_equal(waiter, top_waiter);
|
}
|
|
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);
|
}
|
|
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;
|
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 (!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 (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) {
|
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 = get_task_struct(rt_mutex_owner(lock));
|
raw_spin_lock(&task->pi_lock);
|
|
/*
|
* No requeue [11] here. We just do deadlock detection.
|
*
|
* [12] Store whether owner is blocked
|
* itself. Decision is made after dropping the locks
|
*/
|
next_lock = task_blocked_on_lock(task);
|
/*
|
* Get the top waiter for the next iteration
|
*/
|
top_waiter = rt_mutex_top_waiter(lock);
|
|
/* [13] Drop locks */
|
raw_spin_unlock(&task->pi_lock);
|
raw_spin_unlock_irq(&lock->wait_lock);
|
|
/* If owner is not blocked, end of chain. */
|
if (!next_lock)
|
goto out_put_task;
|
goto again;
|
}
|
|
/*
|
* Store the current top waiter before doing the requeue
|
* operation on @lock. We need it for the boost/deboost
|
* decision below.
|
*/
|
prerequeue_top_waiter = rt_mutex_top_waiter(lock);
|
|
/* [7] Requeue the waiter in the lock waiter tree. */
|
rt_mutex_dequeue(lock, waiter);
|
|
/*
|
* Update the waiter prio fields now that we're dequeued.
|
*
|
* These values can have changed through either:
|
*
|
* sys_sched_set_scheduler() / sys_sched_setattr()
|
*
|
* or
|
*
|
* DL CBS enforcement advancing the effective deadline.
|
*
|
* Even though pi_waiters also uses these fields, and that tree is only
|
* updated in [11], we can do this here, since we hold [L], which
|
* serializes all pi_waiters access and rb_erase() does not care about
|
* the values of the node being removed.
|
*/
|
waiter->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)) {
|
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_irq(&lock->wait_lock);
|
return 0;
|
}
|
|
/* [10] Grab the next task, i.e. the owner of @lock */
|
task = get_task_struct(rt_mutex_owner(lock));
|
raw_spin_lock(&task->pi_lock);
|
|
/* [11] requeue the pi waiters if necessary */
|
if (waiter == rt_mutex_top_waiter(lock)) {
|
/*
|
* The waiter became the new top (highest priority)
|
* waiter on the lock. Replace the previous top waiter
|
* in the owner tasks pi waiters tree with this waiter
|
* and adjust the priority of the owner.
|
*/
|
rt_mutex_dequeue_pi(task, prerequeue_top_waiter);
|
rt_mutex_enqueue_pi(task, waiter);
|
rt_mutex_adjust_prio(task);
|
|
} else if (prerequeue_top_waiter == waiter) {
|
/*
|
* The waiter was the top waiter on the lock, but is
|
* no longer the top 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
|
* @mode: Lock steal mode (STEAL_NORMAL, STEAL_LATERAL)
|
*/
|
static int __try_to_take_rt_mutex(struct rt_mutex *lock,
|
struct task_struct *task,
|
struct rt_mutex_waiter *waiter, int mode)
|
{
|
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,
|
* or its peer when lateral steal is allowed, give up.
|
*/
|
if (!rt_mutex_steal(lock, waiter, mode))
|
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 the top waiter
|
* priority (kernel view), or equal to it when a
|
* lateral steal is forbidden, @task lost.
|
*/
|
if (!rt_mutex_steal(lock, task_to_waiter(task), 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 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;
|
}
|
|
#ifdef CONFIG_PREEMPT_RT
|
/*
|
* 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_acquire(lock, NULL, current)))
|
return;
|
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_release(lock, current, NULL)))
|
return;
|
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
|
|
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.
|
*/
|
void __sched rt_spin_lock_slowlock_locked(struct rt_mutex *lock,
|
struct rt_mutex_waiter *waiter,
|
unsigned long flags)
|
{
|
struct task_struct *lock_owner, *self = current;
|
struct rt_mutex_waiter *top_waiter;
|
int ret;
|
|
if (__try_to_take_rt_mutex(lock, self, NULL, STEAL_LATERAL))
|
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().
|
*/
|
raw_spin_lock(&self->pi_lock);
|
self->saved_state = self->state;
|
__set_current_state_no_track(TASK_UNINTERRUPTIBLE);
|
raw_spin_unlock(&self->pi_lock);
|
|
ret = task_blocks_on_rt_mutex(lock, waiter, self, RT_MUTEX_MIN_CHAINWALK);
|
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_irqrestore(&lock->wait_lock, flags);
|
|
if (top_waiter != waiter || adaptive_wait(lock, lock_owner))
|
preempt_schedule_lock();
|
|
raw_spin_lock_irqsave(&lock->wait_lock, flags);
|
|
raw_spin_lock(&self->pi_lock);
|
__set_current_state_no_track(TASK_UNINTERRUPTIBLE);
|
raw_spin_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.
|
*/
|
raw_spin_lock(&self->pi_lock);
|
__set_current_state_no_track(self->saved_state);
|
self->saved_state = TASK_RUNNING;
|
raw_spin_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));
|
}
|
|
static void noinline __sched rt_spin_lock_slowlock(struct rt_mutex *lock)
|
{
|
struct rt_mutex_waiter waiter;
|
unsigned long flags;
|
|
rt_mutex_init_waiter(&waiter, true);
|
|
raw_spin_lock_irqsave(&lock->wait_lock, flags);
|
rt_spin_lock_slowlock_locked(lock, &waiter, flags);
|
raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
|
debug_rt_mutex_free_waiter(&waiter);
|
}
|
|
static bool __sched __rt_mutex_unlock_common(struct rt_mutex *lock,
|
struct wake_q_head *wake_q,
|
struct wake_q_head *wq_sleeper);
|
/*
|
* Slow path to release a rt_mutex spin_lock style
|
*/
|
void __sched rt_spin_lock_slowunlock(struct rt_mutex *lock)
|
{
|
unsigned long flags;
|
DEFINE_WAKE_Q(wake_q);
|
DEFINE_WAKE_Q(wake_sleeper_q);
|
bool postunlock;
|
|
raw_spin_lock_irqsave(&lock->wait_lock, flags);
|
postunlock = __rt_mutex_unlock_common(lock, &wake_q, &wake_sleeper_q);
|
raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
|
|
if (postunlock)
|
rt_mutex_postunlock(&wake_q, &wake_sleeper_q);
|
}
|
|
void __lockfunc rt_spin_lock(spinlock_t *lock)
|
{
|
spin_acquire(&lock->dep_map, 0, 0, _RET_IP_);
|
rt_spin_lock_fastlock(&lock->lock, rt_spin_lock_slowlock);
|
rcu_read_lock();
|
migrate_disable();
|
}
|
EXPORT_SYMBOL(rt_spin_lock);
|
|
void __lockfunc __rt_spin_lock(struct rt_mutex *lock)
|
{
|
rt_spin_lock_fastlock(lock, rt_spin_lock_slowlock);
|
}
|
|
#ifdef CONFIG_DEBUG_LOCK_ALLOC
|
void __lockfunc rt_spin_lock_nested(spinlock_t *lock, int subclass)
|
{
|
spin_acquire(&lock->dep_map, subclass, 0, _RET_IP_);
|
rt_spin_lock_fastlock(&lock->lock, rt_spin_lock_slowlock);
|
rcu_read_lock();
|
migrate_disable();
|
}
|
EXPORT_SYMBOL(rt_spin_lock_nested);
|
|
void __lockfunc rt_spin_lock_nest_lock(spinlock_t *lock,
|
struct lockdep_map *nest_lock)
|
{
|
spin_acquire_nest(&lock->dep_map, 0, 0, nest_lock, _RET_IP_);
|
rt_spin_lock_fastlock(&lock->lock, rt_spin_lock_slowlock);
|
rcu_read_lock();
|
migrate_disable();
|
}
|
EXPORT_SYMBOL(rt_spin_lock_nest_lock);
|
#endif
|
|
void __lockfunc rt_spin_unlock(spinlock_t *lock)
|
{
|
/* NOTE: we always pass in '1' for nested, for simplicity */
|
spin_release(&lock->dep_map, _RET_IP_);
|
migrate_enable();
|
rcu_read_unlock();
|
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_lock_unlock(spinlock_t *lock)
|
{
|
spin_lock(lock);
|
spin_unlock(lock);
|
}
|
EXPORT_SYMBOL(rt_spin_lock_unlock);
|
|
int __lockfunc rt_spin_trylock(spinlock_t *lock)
|
{
|
int ret;
|
|
ret = __rt_mutex_trylock(&lock->lock);
|
if (ret) {
|
spin_acquire(&lock->dep_map, 0, 1, _RET_IP_);
|
rcu_read_lock();
|
migrate_disable();
|
}
|
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) {
|
spin_acquire(&lock->dep_map, 0, 1, _RET_IP_);
|
rcu_read_lock();
|
migrate_disable();
|
} else {
|
local_bh_enable();
|
}
|
return ret;
|
}
|
EXPORT_SYMBOL(rt_spin_trylock_bh);
|
|
void
|
__rt_spin_lock_init(spinlock_t *lock, const 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 */
|
|
#ifdef CONFIG_PREEMPT_RT
|
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 = READ_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 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);
|
/*
|
* 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(&task->pi_lock);
|
return -EAGAIN;
|
}
|
|
BUG_ON(rt_mutex_real_waiter(task->pi_blocked_on));
|
|
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 (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(&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 wake_q_head *wake_sleeper_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();
|
if (waiter->savestate)
|
wake_q_add_sleeper(wake_sleeper_q, waiter->task);
|
else
|
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 = NULL;
|
|
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 */
|
if (rt_mutex_real_waiter(owner->pi_blocked_on))
|
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 (!rt_mutex_real_waiter(waiter) ||
|
rt_mutex_waiter_equal(waiter, task_to_waiter(task))) {
|
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);
|
}
|
|
void rt_mutex_init_waiter(struct rt_mutex_waiter *waiter, bool savestate)
|
{
|
debug_rt_mutex_init_waiter(waiter);
|
RB_CLEAR_NODE(&waiter->pi_tree_entry);
|
RB_CLEAR_NODE(&waiter->tree_entry);
|
waiter->task = NULL;
|
waiter->savestate = savestate;
|
}
|
|
/**
|
* __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,
|
struct ww_acquire_ctx *ww_ctx)
|
{
|
int ret = 0;
|
|
trace_android_vh_rtmutex_wait_start(lock);
|
for (;;) {
|
/* Try to acquire the lock: */
|
if (try_to_take_rt_mutex(lock, current, waiter))
|
break;
|
|
if (timeout && !timeout->task) {
|
ret = -ETIMEDOUT;
|
break;
|
}
|
if (signal_pending_state(state, current)) {
|
ret = -EINTR;
|
break;
|
}
|
|
if (ww_ctx && ww_ctx->acquired > 0) {
|
ret = __mutex_lock_check_stamp(lock, ww_ctx);
|
if (ret)
|
break;
|
}
|
|
raw_spin_unlock_irq(&lock->wait_lock);
|
|
schedule();
|
|
raw_spin_lock_irq(&lock->wait_lock);
|
set_current_state(state);
|
}
|
|
trace_android_vh_rtmutex_wait_finish(lock);
|
__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;
|
|
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
|
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.rb_root,
|
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
|
|
int __sched rt_mutex_slowlock_locked(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;
|
|
#ifdef CONFIG_PREEMPT_RT
|
if (ww_ctx) {
|
struct ww_mutex *ww;
|
|
ww = container_of(lock, struct ww_mutex, base.lock);
|
if (unlikely(ww_ctx == READ_ONCE(ww->ctx)))
|
return -EALREADY;
|
}
|
#endif
|
|
/* 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);
|
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,
|
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);
|
remove_waiter(lock, waiter);
|
/* ww_mutex wants to report EDEADLK/EALREADY, let it */
|
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);
|
return ret;
|
}
|
|
/*
|
* 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;
|
unsigned long flags;
|
int ret = 0;
|
|
rt_mutex_init_waiter(&waiter, false);
|
|
/*
|
* Technically we could use raw_spin_[un]lock_irq() here, but this can
|
* be called in early boot if the cmpxchg() fast path is disabled
|
* (debug, no architecture support). In this case we will acquire the
|
* rtmutex with lock->wait_lock held. But we cannot unconditionally
|
* enable interrupts in that early boot case. So we need to use the
|
* irqsave/restore variants.
|
*/
|
raw_spin_lock_irqsave(&lock->wait_lock, flags);
|
|
ret = rt_mutex_slowlock_locked(lock, state, timeout, chwalk, ww_ctx,
|
&waiter);
|
|
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,
|
struct wake_q_head *wake_sleeper_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, wake_sleeper_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,
|
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_acquire(lock, NULL, current)))
|
return 0;
|
|
return slowfn(lock, state, NULL, RT_MUTEX_MIN_CHAINWALK, ww_ctx);
|
}
|
|
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 top-waiter and re-enables preemption.
|
*/
|
void rt_mutex_postunlock(struct wake_q_head *wake_q,
|
struct wake_q_head *wake_sleeper_q)
|
{
|
wake_up_q(wake_q);
|
wake_up_q_sleeper(wake_sleeper_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,
|
struct wake_q_head *wq_sleeper))
|
{
|
DEFINE_WAKE_Q(wake_q);
|
DEFINE_WAKE_Q(wake_sleeper_q);
|
|
if (likely(rt_mutex_cmpxchg_release(lock, current, NULL)))
|
return;
|
|
if (slowfn(lock, &wake_q, &wake_sleeper_q))
|
rt_mutex_postunlock(&wake_q, &wake_sleeper_q);
|
}
|
|
int __sched __rt_mutex_lock_state(struct rt_mutex *lock, int state)
|
{
|
might_sleep();
|
return rt_mutex_fastlock(lock, state, NULL, rt_mutex_slowlock);
|
}
|
|
/**
|
* rt_mutex_lock_state - lock a rt_mutex with a given state
|
*
|
* @lock: The rt_mutex to be locked
|
* @state: The state to set when blocking on the rt_mutex
|
*/
|
static inline int __sched rt_mutex_lock_state(struct rt_mutex *lock,
|
unsigned int subclass, int state)
|
{
|
int ret;
|
|
mutex_acquire(&lock->dep_map, subclass, 0, _RET_IP_);
|
ret = __rt_mutex_lock_state(lock, state);
|
if (ret)
|
mutex_release(&lock->dep_map, _RET_IP_);
|
trace_android_vh_record_rtmutex_lock_starttime(current, jiffies);
|
|
return ret;
|
}
|
|
static inline void __rt_mutex_lock(struct rt_mutex *lock, unsigned int subclass)
|
{
|
rt_mutex_lock_state(lock, subclass, TASK_UNINTERRUPTIBLE);
|
}
|
|
#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);
|
|
#else /* !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)
|
{
|
return rt_mutex_lock_state(lock, 0, TASK_INTERRUPTIBLE);
|
}
|
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);
|
}
|
|
int __sched __rt_mutex_trylock(struct rt_mutex *lock)
|
{
|
#ifdef CONFIG_PREEMPT_RT
|
if (WARN_ON_ONCE(in_irq() || in_nmi()))
|
#else
|
if (WARN_ON_ONCE(in_irq() || in_nmi() || in_serving_softirq()))
|
#endif
|
return 0;
|
|
return rt_mutex_fasttrylock(lock, rt_mutex_slowtrylock);
|
}
|
|
/**
|
* 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;
|
|
ret = __rt_mutex_trylock(lock);
|
if (ret)
|
mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
|
else
|
trace_android_vh_record_rtmutex_lock_starttime(current, jiffies);
|
|
return ret;
|
}
|
|
void __sched __rt_mutex_unlock(struct rt_mutex *lock)
|
{
|
rt_mutex_fastunlock(lock, rt_mutex_slowunlock);
|
}
|
|
/**
|
* 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, _RET_IP_);
|
__rt_mutex_unlock(lock);
|
trace_android_vh_record_rtmutex_lock_starttime(current, 0);
|
}
|
EXPORT_SYMBOL_GPL(rt_mutex_unlock);
|
|
static bool __sched __rt_mutex_unlock_common(struct rt_mutex *lock,
|
struct wake_q_head *wake_q,
|
struct wake_q_head *wq_sleeper)
|
{
|
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, wq_sleeper, lock);
|
|
return true; /* call postunlock() */
|
}
|
|
/**
|
* 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,
|
struct wake_q_head *wq_sleeper)
|
{
|
return __rt_mutex_unlock_common(lock, wake_q, wq_sleeper);
|
}
|
|
void __sched rt_mutex_futex_unlock(struct rt_mutex *lock)
|
{
|
DEFINE_WAKE_Q(wake_q);
|
DEFINE_WAKE_Q(wake_sleeper_q);
|
unsigned long flags;
|
bool postunlock;
|
|
raw_spin_lock_irqsave(&lock->wait_lock, flags);
|
postunlock = __rt_mutex_futex_unlock(lock, &wake_q, &wake_sleeper_q);
|
raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
|
|
if (postunlock)
|
rt_mutex_postunlock(&wake_q, &wake_sleeper_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));
|
}
|
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(__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);
|
#ifdef CONFIG_DEBUG_SPINLOCK
|
/*
|
* get another key class for the wait_lock. LOCK_PI and UNLOCK_PI is
|
* holding the ->wait_lock of the proxy_lock while unlocking a sleeping
|
* lock.
|
*/
|
raw_spin_lock_init(&lock->wait_lock);
|
#endif
|
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)
|
{
|
debug_rt_mutex_proxy_unlock(lock);
|
rt_mutex_set_owner(lock, NULL);
|
}
|
|
static void fixup_rt_mutex_blocked(struct rt_mutex *lock)
|
{
|
struct task_struct *tsk = current;
|
/*
|
* RT has a problem here when the wait got interrupted by a timeout
|
* or a signal. task->pi_blocked_on is still set. The task must
|
* acquire the hash bucket lock when returning from this function.
|
*
|
* If the hash bucket lock is contended then the
|
* BUG_ON(rt_mutex_real_waiter(task->pi_blocked_on)) in
|
* task_blocks_on_rt_mutex() will trigger. This can be avoided by
|
* clearing task->pi_blocked_on which removes the task from the
|
* boosting chain of the rtmutex. That's correct because the task
|
* is not longer blocked on it.
|
*/
|
raw_spin_lock(&tsk->pi_lock);
|
tsk->pi_blocked_on = NULL;
|
raw_spin_unlock(&tsk->pi_lock);
|
}
|
|
/**
|
* __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
|
*
|
* Starts the rt_mutex acquire; it enqueues the @waiter and does deadlock
|
* detection. It does not wait, see rt_mutex_wait_proxy_lock() for that.
|
*
|
* NOTE: does _NOT_ remove the @waiter on failure; must either call
|
* rt_mutex_wait_proxy_lock() or rt_mutex_cleanup_proxy_lock() after this.
|
*
|
* Returns:
|
* 0 - task blocked on lock
|
* 1 - acquired the lock for task, caller should wake it up
|
* <0 - error
|
*
|
* Special API call for PI-futex support.
|
*/
|
int __rt_mutex_start_proxy_lock(struct rt_mutex *lock,
|
struct rt_mutex_waiter *waiter,
|
struct task_struct *task)
|
{
|
int ret;
|
|
lockdep_assert_held(&lock->wait_lock);
|
|
if (try_to_take_rt_mutex(lock, task, NULL))
|
return 1;
|
|
#ifdef CONFIG_PREEMPT_RT
|
/*
|
* 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(&task->pi_lock);
|
if (task->pi_blocked_on) {
|
raw_spin_unlock(&task->pi_lock);
|
return -EAGAIN;
|
}
|
task->pi_blocked_on = PI_REQUEUE_INPROGRESS;
|
raw_spin_unlock(&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 (ret)
|
fixup_rt_mutex_blocked(lock);
|
|
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
|
*
|
* Starts the rt_mutex acquire; it enqueues the @waiter and does deadlock
|
* detection. It does not wait, see rt_mutex_wait_proxy_lock() for that.
|
*
|
* NOTE: unlike __rt_mutex_start_proxy_lock this _DOES_ remove the @waiter
|
* on failure.
|
*
|
* Returns:
|
* 0 - task blocked on lock
|
* 1 - acquired the lock for task, caller should wake it up
|
* <0 - error
|
*
|
* Special API call for PI-futex 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);
|
if (unlikely(ret))
|
remove_waiter(lock, waiter);
|
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 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, NULL);
|
/*
|
* try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
|
* have to fix that up.
|
*/
|
fixup_rt_mutex_waiters(lock);
|
if (ret)
|
fixup_rt_mutex_blocked(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_start_proxy_lock() or
|
* 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;
|
}
|
|
static inline int
|
ww_mutex_deadlock_injection(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
|
{
|
#ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
|
unsigned int 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
|
int __sched
|
ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
|
{
|
int ret;
|
|
might_sleep();
|
|
mutex_acquire_nest(&lock->base.dep_map, 0, 0,
|
ctx ? &ctx->dep_map : NULL, _RET_IP_);
|
ret = rt_mutex_slowlock(&lock->base.lock, TASK_INTERRUPTIBLE, NULL, 0,
|
ctx);
|
if (ret)
|
mutex_release(&lock->base.dep_map, _RET_IP_);
|
else if (!ret && ctx && ctx->acquired > 1)
|
return ww_mutex_deadlock_injection(lock, ctx);
|
|
return ret;
|
}
|
EXPORT_SYMBOL(ww_mutex_lock_interruptible);
|
|
int __sched
|
ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
|
{
|
int ret;
|
|
might_sleep();
|
|
mutex_acquire_nest(&lock->base.dep_map, 0, 0,
|
ctx ? &ctx->dep_map : NULL, _RET_IP_);
|
ret = rt_mutex_slowlock(&lock->base.lock, TASK_UNINTERRUPTIBLE, NULL, 0,
|
ctx);
|
if (ret)
|
mutex_release(&lock->base.dep_map, _RET_IP_);
|
else if (!ret && ctx && ctx->acquired > 1)
|
return ww_mutex_deadlock_injection(lock, ctx);
|
|
return ret;
|
}
|
EXPORT_SYMBOL(ww_mutex_lock);
|
|
void __sched ww_mutex_unlock(struct ww_mutex *lock)
|
{
|
/*
|
* The unlocking fastpath is the 0->1 transition from 'locked'
|
* into 'unlocked' state:
|
*/
|
if (lock->ctx) {
|
#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, _RET_IP_);
|
__rt_mutex_unlock(&lock->base.lock);
|
}
|
EXPORT_SYMBOL(ww_mutex_unlock);
|
|
int __rt_mutex_owner_current(struct rt_mutex *lock)
|
{
|
return rt_mutex_owner(lock) == current;
|
}
|
EXPORT_SYMBOL(__rt_mutex_owner_current);
|
#endif
|
