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locking/mutex: Use acquire/release semantics

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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>
This commit is contained in:
Davidlohr Bueso
2015-09-30 13:03:12 -07:00
committed by Ingo Molnar
parent 63ab7bd0d4
commit 81a43adae3
3 changed files with 14 additions and 13 deletions
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9
kernel/locking/mutex.c
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@@ -277,7 +277,7 @@ static inline int mutex_can_spin_on_owner(struct mutex *lock)
static inline bool mutex_try_to_acquire(struct mutex *lock)
{
return !mutex_is_locked(lock) &&
(atomic_cmpxchg(&lock->count, 1, 0) == 1);
(atomic_cmpxchg_acquire(&lock->count, 1, 0) == 1);
}
/*
@@ -529,7 +529,8 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
* 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(&lock->count, 0) == 1))
if (!mutex_is_locked(lock) &&
(atomic_xchg_acquire(&lock->count, 0) == 1))
goto skip_wait;
debug_mutex_lock_common(lock, &waiter);
@@ -553,7 +554,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
* non-negative in order to avoid unnecessary xchg operations:
*/
if (atomic_read(&lock->count) >= 0 &&
(atomic_xchg(&lock->count, -1) == 1))
(atomic_xchg_acquire(&lock->count, -1) == 1))
break;
/*
@@ -867,7 +868,7 @@ static inline int __mutex_trylock_slowpath(atomic_t *lock_count)
spin_lock_mutex(&lock->wait_lock, flags);
prev = atomic_xchg(&lock->count, -1);
prev = atomic_xchg_acquire(&lock->count, -1);
if (likely(prev == 1)) {
mutex_set_owner(lock);
mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);