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.
The change on the unlock side is more for documentation purpose than
is actually needed.
Suggested-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Waiman Long <Waiman.Long@xxxxxxx>
---
kernel/locking/osq_lock.c | 7 ++++++-
1 files changed, 6 insertions(+), 1 deletions(-)
diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c
index 05a3785..d957b90 100644
--- a/kernel/locking/osq_lock.c
+++ b/kernel/locking/osq_lock.c
@@ -124,6 +124,11 @@ bool osq_lock(struct optimistic_spin_queue *lock)
cpu_relax_lowlatency();
}
+ /*
+ * Add an acquire memory barrier for pairing with the release barrier
+ * in unlock.
+ */
+ smp_acquire__after_ctrl_dep();
return true;
unqueue:
@@ -198,7 +203,7 @@ 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
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