Re: [RFC PATCH-tip v2 1/6] locking/osq: Make lock/unlock proper acquire/release barrier
From: Davidlohr Bueso <dave@stgolabs.net>
Date: 2016-06-15 16:57:16
Also in:
linux-alpha, linux-s390, lkml
On Tue, 14 Jun 2016, Waiman Long wrote:
quoted hunk ↗ jump to hunk
The osq_lock() and osq_unlock() function may not provide the necessary acquire and release barrier in some cases. This patch makes sure that the proper barriers are provided when osq_lock() is successful or when osq_unlock() is called. Signed-off-by: Waiman Long <redacted> --- kernel/locking/osq_lock.c | 4 ++-- 1 files changed, 2 insertions(+), 2 deletions(-)diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c index 05a3785..7dd4ee5 100644 --- a/kernel/locking/osq_lock.c +++ b/kernel/locking/osq_lock.c@@ -115,7 +115,7 @@ bool osq_lock(struct optimistic_spin_queue *lock)* cmpxchg in an attempt to undo our queueing. */ - while (!READ_ONCE(node->locked)) { + while (!smp_load_acquire(&node->locked)) {
Hmm this being a polling path, that barrier can get pretty expensive and last I checked it was unnecessary: 036cc30c6b6 (locking/osq: No need for load/acquire when acquire-polling) Thanks, Davidlohr