[tip:locking/core] locking/pv-qspinlock: Use cmpxchg_release() in __pv_queued_spin_unlock()

[tip-bot for Pan Xinhui]

Commit-ID:  b193049375b04df3ada8c3347b7083db95918bc3
Gitweb: http://git.kernel.org/tip/b193049375b04df3ada8c3347b7083db95918bc3
Author: Pan Xinhui 
AuthorDate: Mon, 19 Sep 2016 05:23:52 -0400
Committer:  Ingo Molnar 
CommitDate: Thu, 22 Sep 2016 15:25:51 +0200

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 
Signed-off-by: Pan Xinhui 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: b...@kernel.crashing.org
Cc: linuxppc-...@lists.ozlabs.org
Cc: m...@ellerman.id.au
Cc: paul...@linux.vnet.ibm.com
Cc: pau...@samba.org
Cc: virtualizat...@lists.linux-foundation.org
Cc: waiman.l...@hpe.com
Link: 
http://lkml.kernel.org/r/1474277037-15200-2-git-send-email-xinhui@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar 
---
 kernel/locking/qspinlock_paravirt.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/locking/qspinlock_paravirt.h 
b/kernel/locking/qspinlock_paravirt.h
index 3acf16d..e3b5520 100644
--- a/kernel/locking/qspinlock_paravirt.h
+++ b/kernel/locking/qspinlock_paravirt.h
@@ -540,7 +540,7 @@ __visible void __pv_queued_spin_unlock(struct qspinlock 
*lock)
 * unhash. Otherwise it would be possible to have multiple @lock
 * entries, which would be BAD.
 */
-   locked = cmpxchg(>locked, _Q_LOCKED_VAL, 0);
+   locked = cmpxchg_release(>locked, _Q_LOCKED_VAL, 0);
if (likely(locked == _Q_LOCKED_VAL))
return;
 

[tip:locking/core] locking/pv-qspinlock: Use cmpxchg_release() in __pv_queued_spin_unlock()

[tip-bot for Pan Xinhui]

Commit-ID:  b193049375b04df3ada8c3347b7083db95918bc3
Gitweb: http://git.kernel.org/tip/b193049375b04df3ada8c3347b7083db95918bc3
Author: Pan Xinhui 
AuthorDate: Mon, 19 Sep 2016 05:23:52 -0400
Committer:  Ingo Molnar 
CommitDate: Thu, 22 Sep 2016 15:25:51 +0200

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 
Signed-off-by: Pan Xinhui 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: b...@kernel.crashing.org
Cc: linuxppc-...@lists.ozlabs.org
Cc: m...@ellerman.id.au
Cc: paul...@linux.vnet.ibm.com
Cc: pau...@samba.org
Cc: virtualizat...@lists.linux-foundation.org
Cc: waiman.l...@hpe.com
Link: 
http://lkml.kernel.org/r/1474277037-15200-2-git-send-email-xinhui@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar 
---
 kernel/locking/qspinlock_paravirt.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/locking/qspinlock_paravirt.h 
b/kernel/locking/qspinlock_paravirt.h
index 3acf16d..e3b5520 100644
--- a/kernel/locking/qspinlock_paravirt.h
+++ b/kernel/locking/qspinlock_paravirt.h
@@ -540,7 +540,7 @@ __visible void __pv_queued_spin_unlock(struct qspinlock 
*lock)
 * unhash. Otherwise it would be possible to have multiple @lock
 * entries, which would be BAD.
 */
-   locked = cmpxchg(>locked, _Q_LOCKED_VAL, 0);
+   locked = cmpxchg_release(>locked, _Q_LOCKED_VAL, 0);
if (likely(locked == _Q_LOCKED_VAL))
return;