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locking/pv-qspinlock: Use cmpxchg_release() in __pv_queued_spin_unlock()
cmpxchg_release() is more lighweight than cmpxchg() on some archs(e.g. PPC), moreover, in __pv_queued_spin_unlock() we only needs a RELEASE in the fast path(pairing with *_try_lock() or *_lock()). And the slow path has smp_store_release too. So it's safe to use cmpxchg_release here. Suggested-by: Boqun Feng <boqun.feng@gmail.com> Signed-off-by: Pan Xinhui <xinhui.pan@linux.vnet.ibm.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: benh@kernel.crashing.org Cc: linuxppc-dev@lists.ozlabs.org Cc: mpe@ellerman.id.au Cc: paulmck@linux.vnet.ibm.com Cc: paulus@samba.org Cc: virtualization@lists.linux-foundation.org Cc: waiman.long@hpe.com Link: http://lkml.kernel.org/r/1474277037-15200-2-git-send-email-xinhui.pan@linux.vnet.ibm.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
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@ -540,7 +540,7 @@ __visible void __pv_queued_spin_unlock(struct qspinlock *lock)
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* unhash. Otherwise it would be possible to have multiple @lock
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* entries, which would be BAD.
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*/
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locked = cmpxchg(&l->locked, _Q_LOCKED_VAL, 0);
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locked = cmpxchg_release(&l->locked, _Q_LOCKED_VAL, 0);
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if (likely(locked == _Q_LOCKED_VAL))
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return;
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