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authorWill Deacon <will.deacon@arm.com>2018-04-26 11:34:23 +0100
committerIngo Molnar <mingo@kernel.org>2018-04-27 09:48:50 +0200
commitc131a198c497db436b558ac5e9a140cdcb91b304 (patch)
tree9f213e959da1d64f45dd7748f94c9d7146d888d4 /kernel/locking
parent7f56b58a92aaf2cab049f32a19af7cc57a3972f2 (diff)
downloadlinux-c131a198c497db436b558ac5e9a140cdcb91b304.tar.bz2
locking/qspinlock: Use smp_cond_load_relaxed() to wait for next node
When a locker reaches the head of the queue and takes the lock, a concurrent locker may enqueue and force the lock holder to spin whilst its node->next field is initialised. Rather than open-code a READ_ONCE/cpu_relax() loop, this can be implemented using smp_cond_load_relaxed() instead. Signed-off-by: Will Deacon <will.deacon@arm.com> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Waiman Long <longman@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: boqun.feng@gmail.com Cc: linux-arm-kernel@lists.infradead.org Cc: paulmck@linux.vnet.ibm.com Link: http://lkml.kernel.org/r/1524738868-31318-10-git-send-email-will.deacon@arm.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/locking')
-rw-r--r--kernel/locking/qspinlock.c6
1 files changed, 2 insertions, 4 deletions
diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c
index 56af1fa9874d..d6c3b029bd93 100644
--- a/kernel/locking/qspinlock.c
+++ b/kernel/locking/qspinlock.c
@@ -483,10 +483,8 @@ locked:
/*
* contended path; wait for next if not observed yet, release.
*/
- if (!next) {
- while (!(next = READ_ONCE(node->next)))
- cpu_relax();
- }
+ if (!next)
+ next = smp_cond_load_relaxed(&node->next, (VAL));
arch_mcs_spin_unlock_contended(&next->locked);
pv_kick_node(lock, next);