linux/kernel/locking/mutex.c
Davidlohr Bueso 81a43adae3 locking/mutex: Use acquire/release semantics
As of 654672d4ba (locking/atomics: Add _{acquire|release|relaxed}()
variants of some atomic operations) and 6d79ef2d30 (locking, asm-generic:
Add _{relaxed|acquire|release}() variants for 'atomic_long_t'), weakly
ordered archs can benefit from more relaxed use of barriers when locking
and unlocking, instead of regular full barrier semantics. While currently
only arm64 supports such optimizations, updating corresponding locking
primitives serves for other archs to immediately benefit as well, once the
necessary machinery is implemented of course.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Paul E.McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/1443643395-17016-3-git-send-email-dave@stgolabs.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-10-06 17:28:20 +02:00

974 lines
25 KiB
C

/*
* kernel/locking/mutex.c
*
* Mutexes: blocking mutual exclusion locks
*
* Started by Ingo Molnar:
*
* Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
*
* Many thanks to Arjan van de Ven, Thomas Gleixner, Steven Rostedt and
* David Howells for suggestions and improvements.
*
* - Adaptive spinning for mutexes by Peter Zijlstra. (Ported to mainline
* from the -rt tree, where it was originally implemented for rtmutexes
* by Steven Rostedt, based on work by Gregory Haskins, Peter Morreale
* and Sven Dietrich.
*
* Also see Documentation/locking/mutex-design.txt.
*/
#include <linux/mutex.h>
#include <linux/ww_mutex.h>
#include <linux/sched.h>
#include <linux/sched/rt.h>
#include <linux/export.h>
#include <linux/spinlock.h>
#include <linux/interrupt.h>
#include <linux/debug_locks.h>
#include <linux/osq_lock.h>
/*
* In the DEBUG case we are using the "NULL fastpath" for mutexes,
* which forces all calls into the slowpath:
*/
#ifdef CONFIG_DEBUG_MUTEXES
# include "mutex-debug.h"
# include <asm-generic/mutex-null.h>
/*
* Must be 0 for the debug case so we do not do the unlock outside of the
* wait_lock region. debug_mutex_unlock() will do the actual unlock in this
* case.
*/
# undef __mutex_slowpath_needs_to_unlock
# define __mutex_slowpath_needs_to_unlock() 0
#else
# include "mutex.h"
# include <asm/mutex.h>
#endif
void
__mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
{
atomic_set(&lock->count, 1);
spin_lock_init(&lock->wait_lock);
INIT_LIST_HEAD(&lock->wait_list);
mutex_clear_owner(lock);
#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
osq_lock_init(&lock->osq);
#endif
debug_mutex_init(lock, name, key);
}
EXPORT_SYMBOL(__mutex_init);
#ifndef CONFIG_DEBUG_LOCK_ALLOC
/*
* We split the mutex lock/unlock logic into separate fastpath and
* slowpath functions, to reduce the register pressure on the fastpath.
* We also put the fastpath first in the kernel image, to make sure the
* branch is predicted by the CPU as default-untaken.
*/
__visible void __sched __mutex_lock_slowpath(atomic_t *lock_count);
/**
* mutex_lock - acquire the mutex
* @lock: the mutex to be acquired
*
* Lock the mutex exclusively for this task. If the mutex is not
* available right now, it will sleep until it can get it.
*
* The mutex must later on be released by the same task that
* acquired it. Recursive locking is not allowed. The task
* may not exit without first unlocking the mutex. Also, kernel
* memory where the mutex resides must not be freed with
* the mutex still locked. The mutex must first be initialized
* (or statically defined) before it can be locked. memset()-ing
* the mutex to 0 is not allowed.
*
* ( The CONFIG_DEBUG_MUTEXES .config option turns on debugging
* checks that will enforce the restrictions and will also do
* deadlock debugging. )
*
* This function is similar to (but not equivalent to) down().
*/
void __sched mutex_lock(struct mutex *lock)
{
might_sleep();
/*
* The locking fastpath is the 1->0 transition from
* 'unlocked' into 'locked' state.
*/
__mutex_fastpath_lock(&lock->count, __mutex_lock_slowpath);
mutex_set_owner(lock);
}
EXPORT_SYMBOL(mutex_lock);
#endif
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++;
}
/*
* After acquiring lock with fastpath or when we lost out in contested
* slowpath, set ctx and wake up any waiters so they can recheck.
*
* This function is never called when CONFIG_DEBUG_LOCK_ALLOC is set,
* as the fastpath and opportunistic spinning are disabled in that case.
*/
static __always_inline void
ww_mutex_set_context_fastpath(struct ww_mutex *lock,
struct ww_acquire_ctx *ctx)
{
unsigned long flags;
struct mutex_waiter *cur;
ww_mutex_lock_acquired(lock, ctx);
lock->ctx = ctx;
/*
* The lock->ctx update should be visible on all cores before
* the atomic read is done, otherwise contended waiters might be
* missed. The contended waiters will either see ww_ctx == NULL
* and keep spinning, or it will acquire wait_lock, add itself
* to waiter list and sleep.
*/
smp_mb(); /* ^^^ */
/*
* Check if lock is contended, if not there is nobody to wake up
*/
if (likely(atomic_read(&lock->base.count) == 0))
return;
/*
* Uh oh, we raced in fastpath, wake up everyone in this case,
* so they can see the new lock->ctx.
*/
spin_lock_mutex(&lock->base.wait_lock, flags);
list_for_each_entry(cur, &lock->base.wait_list, list) {
debug_mutex_wake_waiter(&lock->base, cur);
wake_up_process(cur->task);
}
spin_unlock_mutex(&lock->base.wait_lock, flags);
}
/*
* After acquiring lock in the slowpath set ctx and wake up any
* waiters so they can recheck.
*
* Callers must hold the mutex wait_lock.
*/
static __always_inline void
ww_mutex_set_context_slowpath(struct ww_mutex *lock,
struct ww_acquire_ctx *ctx)
{
struct mutex_waiter *cur;
ww_mutex_lock_acquired(lock, ctx);
lock->ctx = ctx;
/*
* Give any possible sleeping processes the chance to wake up,
* so they can recheck if they have to back off.
*/
list_for_each_entry(cur, &lock->base.wait_list, list) {
debug_mutex_wake_waiter(&lock->base, cur);
wake_up_process(cur->task);
}
}
#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
/*
* Look out! "owner" is an entirely speculative pointer
* access and not reliable.
*/
static noinline
bool mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner)
{
bool ret = true;
rcu_read_lock();
while (lock->owner == owner) {
/*
* Ensure we emit the owner->on_cpu, dereference _after_
* checking lock->owner still matches owner. If that fails,
* owner might point to freed memory. If it still matches,
* the rcu_read_lock() ensures the memory stays valid.
*/
barrier();
if (!owner->on_cpu || need_resched()) {
ret = false;
break;
}
cpu_relax_lowlatency();
}
rcu_read_unlock();
return ret;
}
/*
* Initial check for entering the mutex spinning loop
*/
static inline int mutex_can_spin_on_owner(struct mutex *lock)
{
struct task_struct *owner;
int retval = 1;
if (need_resched())
return 0;
rcu_read_lock();
owner = READ_ONCE(lock->owner);
if (owner)
retval = owner->on_cpu;
rcu_read_unlock();
/*
* if lock->owner is not set, the mutex owner may have just acquired
* it and not set the owner yet or the mutex has been released.
*/
return retval;
}
/*
* Atomically try to take the lock when it is available
*/
static inline bool mutex_try_to_acquire(struct mutex *lock)
{
return !mutex_is_locked(lock) &&
(atomic_cmpxchg_acquire(&lock->count, 1, 0) == 1);
}
/*
* Optimistic spinning.
*
* We try to spin for acquisition when we find that the lock owner
* is currently running on a (different) CPU and while we don't
* need to reschedule. The rationale is that if the lock owner is
* running, it is likely to release the lock soon.
*
* Since this needs the lock owner, and this mutex implementation
* doesn't track the owner atomically in the lock field, we need to
* track it non-atomically.
*
* We can't do this for DEBUG_MUTEXES because that relies on wait_lock
* to serialize everything.
*
* The mutex spinners are queued up using MCS lock so that only one
* spinner can compete for the mutex. However, if mutex spinning isn't
* going to happen, there is no point in going through the lock/unlock
* overhead.
*
* Returns true when the lock was taken, otherwise false, indicating
* that we need to jump to the slowpath and sleep.
*/
static bool mutex_optimistic_spin(struct mutex *lock,
struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx)
{
struct task_struct *task = current;
if (!mutex_can_spin_on_owner(lock))
goto done;
/*
* In order to avoid a stampede of mutex spinners trying to
* acquire the mutex all at once, the spinners need to take a
* MCS (queued) lock first before spinning on the owner field.
*/
if (!osq_lock(&lock->osq))
goto done;
while (true) {
struct task_struct *owner;
if (use_ww_ctx && ww_ctx->acquired > 0) {
struct ww_mutex *ww;
ww = container_of(lock, struct ww_mutex, base);
/*
* If ww->ctx is set the contents are undefined, only
* by acquiring wait_lock there is a guarantee that
* they are not invalid when reading.
*
* As such, when deadlock detection needs to be
* performed the optimistic spinning cannot be done.
*/
if (READ_ONCE(ww->ctx))
break;
}
/*
* If there's an owner, wait for it to either
* release the lock or go to sleep.
*/
owner = READ_ONCE(lock->owner);
if (owner && !mutex_spin_on_owner(lock, owner))
break;
/* Try to acquire the mutex if it is unlocked. */
if (mutex_try_to_acquire(lock)) {
lock_acquired(&lock->dep_map, ip);
if (use_ww_ctx) {
struct ww_mutex *ww;
ww = container_of(lock, struct ww_mutex, base);
ww_mutex_set_context_fastpath(ww, ww_ctx);
}
mutex_set_owner(lock);
osq_unlock(&lock->osq);
return true;
}
/*
* When there's no owner, we might have preempted between the
* owner acquiring the lock and setting the owner field. If
* we're an RT task that will live-lock because we won't let
* the owner complete.
*/
if (!owner && (need_resched() || rt_task(task)))
break;
/*
* The cpu_relax() call is a compiler barrier which forces
* everything in this loop to be re-loaded. We don't need
* memory barriers as we'll eventually observe the right
* values at the cost of a few extra spins.
*/
cpu_relax_lowlatency();
}
osq_unlock(&lock->osq);
done:
/*
* If we fell out of the spin path because of need_resched(),
* reschedule now, before we try-lock the mutex. This avoids getting
* scheduled out right after we obtained the mutex.
*/
if (need_resched()) {
/*
* We _should_ have TASK_RUNNING here, but just in case
* we do not, make it so, otherwise we might get stuck.
*/
__set_current_state(TASK_RUNNING);
schedule_preempt_disabled();
}
return false;
}
#else
static bool mutex_optimistic_spin(struct mutex *lock,
struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx)
{
return false;
}
#endif
__visible __used noinline
void __sched __mutex_unlock_slowpath(atomic_t *lock_count);
/**
* mutex_unlock - release the mutex
* @lock: the mutex to be released
*
* Unlock a mutex that has been locked by this task previously.
*
* This function must not be used in interrupt context. Unlocking
* of a not locked mutex is not allowed.
*
* This function is similar to (but not equivalent to) up().
*/
void __sched mutex_unlock(struct mutex *lock)
{
/*
* The unlocking fastpath is the 0->1 transition from 'locked'
* into 'unlocked' state:
*/
#ifndef CONFIG_DEBUG_MUTEXES
/*
* When debugging is enabled we must not clear the owner before time,
* the slow path will always be taken, and that clears the owner field
* after verifying that it was indeed current.
*/
mutex_clear_owner(lock);
#endif
__mutex_fastpath_unlock(&lock->count, __mutex_unlock_slowpath);
}
EXPORT_SYMBOL(mutex_unlock);
/**
* ww_mutex_unlock - release the w/w mutex
* @lock: the mutex to be released
*
* Unlock a mutex that has been locked by this task previously with any of the
* ww_mutex_lock* functions (with or without an acquire context). It is
* forbidden to release the locks after releasing the acquire context.
*
* This function must not be used in interrupt context. Unlocking
* of a unlocked mutex is not allowed.
*/
void __sched ww_mutex_unlock(struct ww_mutex *lock)
{
/*
* 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;
}
#ifndef CONFIG_DEBUG_MUTEXES
/*
* When debugging is enabled we must not clear the owner before time,
* the slow path will always be taken, and that clears the owner field
* after verifying that it was indeed current.
*/
mutex_clear_owner(&lock->base);
#endif
__mutex_fastpath_unlock(&lock->base.count, __mutex_unlock_slowpath);
}
EXPORT_SYMBOL(ww_mutex_unlock);
static inline int __sched
__ww_mutex_lock_check_stamp(struct mutex *lock, struct ww_acquire_ctx *ctx)
{
struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
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;
}
/*
* Lock a mutex (possibly interruptible), slowpath:
*/
static __always_inline int __sched
__mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
struct lockdep_map *nest_lock, unsigned long ip,
struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx)
{
struct task_struct *task = current;
struct mutex_waiter waiter;
unsigned long flags;
int ret;
preempt_disable();
mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip);
if (mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx)) {
/* got the lock, yay! */
preempt_enable();
return 0;
}
spin_lock_mutex(&lock->wait_lock, flags);
/*
* Once more, try to acquire the lock. Only try-lock the mutex if
* it is unlocked to reduce unnecessary xchg() operations.
*/
if (!mutex_is_locked(lock) &&
(atomic_xchg_acquire(&lock->count, 0) == 1))
goto skip_wait;
debug_mutex_lock_common(lock, &waiter);
debug_mutex_add_waiter(lock, &waiter, task_thread_info(task));
/* add waiting tasks to the end of the waitqueue (FIFO): */
list_add_tail(&waiter.list, &lock->wait_list);
waiter.task = task;
lock_contended(&lock->dep_map, ip);
for (;;) {
/*
* Lets try to take the lock again - this is needed even if
* we get here for the first time (shortly after failing to
* acquire the lock), to make sure that we get a wakeup once
* it's unlocked. Later on, if we sleep, this is the
* operation that gives us the lock. We xchg it to -1, so
* that when we release the lock, we properly wake up the
* other waiters. We only attempt the xchg if the count is
* non-negative in order to avoid unnecessary xchg operations:
*/
if (atomic_read(&lock->count) >= 0 &&
(atomic_xchg_acquire(&lock->count, -1) == 1))
break;
/*
* got a signal? (This code gets eliminated in the
* TASK_UNINTERRUPTIBLE case.)
*/
if (unlikely(signal_pending_state(state, task))) {
ret = -EINTR;
goto err;
}
if (use_ww_ctx && ww_ctx->acquired > 0) {
ret = __ww_mutex_lock_check_stamp(lock, ww_ctx);
if (ret)
goto err;
}
__set_task_state(task, state);
/* didn't get the lock, go to sleep: */
spin_unlock_mutex(&lock->wait_lock, flags);
schedule_preempt_disabled();
spin_lock_mutex(&lock->wait_lock, flags);
}
__set_task_state(task, TASK_RUNNING);
mutex_remove_waiter(lock, &waiter, current_thread_info());
/* set it to 0 if there are no waiters left: */
if (likely(list_empty(&lock->wait_list)))
atomic_set(&lock->count, 0);
debug_mutex_free_waiter(&waiter);
skip_wait:
/* got the lock - cleanup and rejoice! */
lock_acquired(&lock->dep_map, ip);
mutex_set_owner(lock);
if (use_ww_ctx) {
struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
ww_mutex_set_context_slowpath(ww, ww_ctx);
}
spin_unlock_mutex(&lock->wait_lock, flags);
preempt_enable();
return 0;
err:
mutex_remove_waiter(lock, &waiter, task_thread_info(task));
spin_unlock_mutex(&lock->wait_lock, flags);
debug_mutex_free_waiter(&waiter);
mutex_release(&lock->dep_map, 1, ip);
preempt_enable();
return ret;
}
#ifdef CONFIG_DEBUG_LOCK_ALLOC
void __sched
mutex_lock_nested(struct mutex *lock, unsigned int subclass)
{
might_sleep();
__mutex_lock_common(lock, TASK_UNINTERRUPTIBLE,
subclass, NULL, _RET_IP_, NULL, 0);
}
EXPORT_SYMBOL_GPL(mutex_lock_nested);
void __sched
_mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest)
{
might_sleep();
__mutex_lock_common(lock, TASK_UNINTERRUPTIBLE,
0, nest, _RET_IP_, NULL, 0);
}
EXPORT_SYMBOL_GPL(_mutex_lock_nest_lock);
int __sched
mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass)
{
might_sleep();
return __mutex_lock_common(lock, TASK_KILLABLE,
subclass, NULL, _RET_IP_, NULL, 0);
}
EXPORT_SYMBOL_GPL(mutex_lock_killable_nested);
int __sched
mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass)
{
might_sleep();
return __mutex_lock_common(lock, TASK_INTERRUPTIBLE,
subclass, NULL, _RET_IP_, NULL, 0);
}
EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested);
static inline int
ww_mutex_deadlock_injection(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
{
#ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
unsigned tmp;
if (ctx->deadlock_inject_countdown-- == 0) {
tmp = ctx->deadlock_inject_interval;
if (tmp > UINT_MAX/4)
tmp = UINT_MAX;
else
tmp = tmp*2 + tmp + tmp/2;
ctx->deadlock_inject_interval = tmp;
ctx->deadlock_inject_countdown = tmp;
ctx->contending_lock = lock;
ww_mutex_unlock(lock);
return -EDEADLK;
}
#endif
return 0;
}
int __sched
__ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
{
int ret;
might_sleep();
ret = __mutex_lock_common(&lock->base, TASK_UNINTERRUPTIBLE,
0, &ctx->dep_map, _RET_IP_, ctx, 1);
if (!ret && ctx->acquired > 1)
return ww_mutex_deadlock_injection(lock, ctx);
return ret;
}
EXPORT_SYMBOL_GPL(__ww_mutex_lock);
int __sched
__ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
{
int ret;
might_sleep();
ret = __mutex_lock_common(&lock->base, TASK_INTERRUPTIBLE,
0, &ctx->dep_map, _RET_IP_, ctx, 1);
if (!ret && ctx->acquired > 1)
return ww_mutex_deadlock_injection(lock, ctx);
return ret;
}
EXPORT_SYMBOL_GPL(__ww_mutex_lock_interruptible);
#endif
/*
* Release the lock, slowpath:
*/
static inline void
__mutex_unlock_common_slowpath(struct mutex *lock, int nested)
{
unsigned long flags;
/*
* As a performance measurement, release the lock before doing other
* wakeup related duties to follow. This allows other tasks to acquire
* the lock sooner, while still handling cleanups in past unlock calls.
* This can be done as we do not enforce strict equivalence between the
* mutex counter and wait_list.
*
*
* Some architectures leave the lock unlocked in the fastpath failure
* case, others need to leave it locked. In the later case we have to
* unlock it here - as the lock counter is currently 0 or negative.
*/
if (__mutex_slowpath_needs_to_unlock())
atomic_set(&lock->count, 1);
spin_lock_mutex(&lock->wait_lock, flags);
mutex_release(&lock->dep_map, nested, _RET_IP_);
debug_mutex_unlock(lock);
if (!list_empty(&lock->wait_list)) {
/* get the first entry from the wait-list: */
struct mutex_waiter *waiter =
list_entry(lock->wait_list.next,
struct mutex_waiter, list);
debug_mutex_wake_waiter(lock, waiter);
wake_up_process(waiter->task);
}
spin_unlock_mutex(&lock->wait_lock, flags);
}
/*
* Release the lock, slowpath:
*/
__visible void
__mutex_unlock_slowpath(atomic_t *lock_count)
{
struct mutex *lock = container_of(lock_count, struct mutex, count);
__mutex_unlock_common_slowpath(lock, 1);
}
#ifndef CONFIG_DEBUG_LOCK_ALLOC
/*
* Here come the less common (and hence less performance-critical) APIs:
* mutex_lock_interruptible() and mutex_trylock().
*/
static noinline int __sched
__mutex_lock_killable_slowpath(struct mutex *lock);
static noinline int __sched
__mutex_lock_interruptible_slowpath(struct mutex *lock);
/**
* mutex_lock_interruptible - acquire the mutex, interruptible
* @lock: the mutex to be acquired
*
* Lock the mutex like mutex_lock(), and return 0 if the mutex has
* been acquired or sleep until the mutex becomes available. If a
* signal arrives while waiting for the lock then this function
* returns -EINTR.
*
* This function is similar to (but not equivalent to) down_interruptible().
*/
int __sched mutex_lock_interruptible(struct mutex *lock)
{
int ret;
might_sleep();
ret = __mutex_fastpath_lock_retval(&lock->count);
if (likely(!ret)) {
mutex_set_owner(lock);
return 0;
} else
return __mutex_lock_interruptible_slowpath(lock);
}
EXPORT_SYMBOL(mutex_lock_interruptible);
int __sched mutex_lock_killable(struct mutex *lock)
{
int ret;
might_sleep();
ret = __mutex_fastpath_lock_retval(&lock->count);
if (likely(!ret)) {
mutex_set_owner(lock);
return 0;
} else
return __mutex_lock_killable_slowpath(lock);
}
EXPORT_SYMBOL(mutex_lock_killable);
__visible void __sched
__mutex_lock_slowpath(atomic_t *lock_count)
{
struct mutex *lock = container_of(lock_count, struct mutex, count);
__mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0,
NULL, _RET_IP_, NULL, 0);
}
static noinline int __sched
__mutex_lock_killable_slowpath(struct mutex *lock)
{
return __mutex_lock_common(lock, TASK_KILLABLE, 0,
NULL, _RET_IP_, NULL, 0);
}
static noinline int __sched
__mutex_lock_interruptible_slowpath(struct mutex *lock)
{
return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, 0,
NULL, _RET_IP_, NULL, 0);
}
static noinline int __sched
__ww_mutex_lock_slowpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
{
return __mutex_lock_common(&lock->base, TASK_UNINTERRUPTIBLE, 0,
NULL, _RET_IP_, ctx, 1);
}
static noinline int __sched
__ww_mutex_lock_interruptible_slowpath(struct ww_mutex *lock,
struct ww_acquire_ctx *ctx)
{
return __mutex_lock_common(&lock->base, TASK_INTERRUPTIBLE, 0,
NULL, _RET_IP_, ctx, 1);
}
#endif
/*
* Spinlock based trylock, we take the spinlock and check whether we
* can get the lock:
*/
static inline int __mutex_trylock_slowpath(atomic_t *lock_count)
{
struct mutex *lock = container_of(lock_count, struct mutex, count);
unsigned long flags;
int prev;
/* No need to trylock if the mutex is locked. */
if (mutex_is_locked(lock))
return 0;
spin_lock_mutex(&lock->wait_lock, flags);
prev = atomic_xchg_acquire(&lock->count, -1);
if (likely(prev == 1)) {
mutex_set_owner(lock);
mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
}
/* Set it back to 0 if there are no waiters: */
if (likely(list_empty(&lock->wait_list)))
atomic_set(&lock->count, 0);
spin_unlock_mutex(&lock->wait_lock, flags);
return prev == 1;
}
/**
* mutex_trylock - try to acquire the mutex, without waiting
* @lock: the mutex to be acquired
*
* Try to acquire the mutex atomically. Returns 1 if the mutex
* has been acquired successfully, and 0 on contention.
*
* NOTE: this function follows the spin_trylock() convention, so
* it is negated from the down_trylock() return values! Be careful
* about this when converting semaphore users to mutexes.
*
* This function must not be used in interrupt context. The
* mutex must be released by the same task that acquired it.
*/
int __sched mutex_trylock(struct mutex *lock)
{
int ret;
ret = __mutex_fastpath_trylock(&lock->count, __mutex_trylock_slowpath);
if (ret)
mutex_set_owner(lock);
return ret;
}
EXPORT_SYMBOL(mutex_trylock);
#ifndef CONFIG_DEBUG_LOCK_ALLOC
int __sched
__ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
{
int ret;
might_sleep();
ret = __mutex_fastpath_lock_retval(&lock->base.count);
if (likely(!ret)) {
ww_mutex_set_context_fastpath(lock, ctx);
mutex_set_owner(&lock->base);
} else
ret = __ww_mutex_lock_slowpath(lock, ctx);
return ret;
}
EXPORT_SYMBOL(__ww_mutex_lock);
int __sched
__ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
{
int ret;
might_sleep();
ret = __mutex_fastpath_lock_retval(&lock->base.count);
if (likely(!ret)) {
ww_mutex_set_context_fastpath(lock, ctx);
mutex_set_owner(&lock->base);
} else
ret = __ww_mutex_lock_interruptible_slowpath(lock, ctx);
return ret;
}
EXPORT_SYMBOL(__ww_mutex_lock_interruptible);
#endif
/**
* atomic_dec_and_mutex_lock - return holding mutex if we dec to 0
* @cnt: the atomic which we are to dec
* @lock: the mutex to return holding if we dec to 0
*
* return true and hold lock if we dec to 0, return false otherwise
*/
int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock)
{
/* dec if we can't possibly hit 0 */
if (atomic_add_unless(cnt, -1, 1))
return 0;
/* we might hit 0, so take the lock */
mutex_lock(lock);
if (!atomic_dec_and_test(cnt)) {
/* when we actually did the dec, we didn't hit 0 */
mutex_unlock(lock);
return 0;
}
/* we hit 0, and we hold the lock */
return 1;
}
EXPORT_SYMBOL(atomic_dec_and_mutex_lock);