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locking/qspinlock: Use atomic_sub_return_release() in queued_spin_unlock() 

The existing version uses a heavy barrier while only release semantics
is required. So use atomic_sub_return_release() instead.

Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Pan Xinhui <xinhui.pan@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: arnd@arndb.de
Cc: waiman.long@hp.com
Link: http://lkml.kernel.org/r/1464943094-3129-1-git-send-email-xinhui.pan@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
hifive-unleashed-5.1
Pan Xinhui 2016-06-03 16:38:14 +08:00 committed by Ingo Molnar
parent 6428671bae
commit ca50e426f9
1 changed files with 2 additions and 3 deletions
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5
include/asm-generic/qspinlock.h
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@ -111,10 +111,9 @@ static __always_inline void queued_spin_lock(struct qspinlock *lock)
static __always_inline void queued_spin_unlock(struct qspinlock *lock)
{
/*
* smp_mb__before_atomic() in order to guarantee release semantics
* unlock() needs release semantics:
*/
smp_mb__before_atomic();
atomic_sub(_Q_LOCKED_VAL, &lock->val);
(void)atomic_sub_return_release(_Q_LOCKED_VAL, &lock->val);
}
#endif