From 3552a07a9c4aea32cc092fadf10a186c84ed8a61 Mon Sep 17 00:00:00 2001 From: Davidlohr Bueso Date: Wed, 30 Sep 2015 13:03:14 -0700 Subject: [PATCH] locking/mcs: Use acquire/release semantics As of 654672d4ba1 (locking/atomics: Add _{acquire|release|relaxed}() variants of some atomic operations) and 6d79ef2d30e (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 Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Thomas Gleixner Cc: Andrew Morton Cc: Linus Torvalds Cc: Paul E. McKenney Cc: Paul E.McKenney Cc: Peter Zijlstra Cc: Will Deacon Cc: linux-kernel@vger.kernel.org Link: http://lkml.kernel.org/r/1443643395-17016-5-git-send-email-dave@stgolabs.net Signed-off-by: Ingo Molnar --- kernel/locking/mcs_spinlock.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/locking/mcs_spinlock.h b/kernel/locking/mcs_spinlock.h index fd91aaa4554c..5b9102a47ea5 100644 --- a/kernel/locking/mcs_spinlock.h +++ b/kernel/locking/mcs_spinlock.h @@ -67,7 +67,7 @@ void mcs_spin_lock(struct mcs_spinlock **lock, struct mcs_spinlock *node) node->locked = 0; node->next = NULL; - prev = xchg(lock, node); + prev = xchg_acquire(lock, node); if (likely(prev == NULL)) { /* * Lock acquired, don't need to set node->locked to 1. Threads @@ -98,7 +98,7 @@ void mcs_spin_unlock(struct mcs_spinlock **lock, struct mcs_spinlock *node) /* * Release the lock by setting it to NULL */ - if (likely(cmpxchg(lock, node, NULL) == node)) + if (likely(cmpxchg_release(lock, node, NULL) == node)) return; /* Wait until the next pointer is set */ while (!(next = READ_ONCE(node->next)))