[RFC PATCH-tip v2 1/6] locking/osq: Make lock/unlock proper acquire/release barrier

Waiman Long
2016-06-14T22:48:04Z

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 <Waiman.Long@hpe.com>
---
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)) {
/*
* If we need to reschedule bail... so we can block.
*/
@@ -198,7 +198,7 @@ void osq_unlock(struct optimistic_spin_queue *lock)
* Second most likely case.
*/
node = this_cpu_ptr(&osq_node);
- next = xchg(&node->next, NULL);
+ next = xchg_release(&node->next, NULL);
if (next) {
WRITE_ONCE(next->locked, 1);
return;
--
1.7.1