[PATCH] locking/osq_lock: Use READ_ONCE() for node->prev

[Yu Peng]

osq_lock() consults node->prev in the vcpu_is_preempted() heuristic while
a concurrent predecessor may update it via WRITE_ONCE(next->prev, prev)
during unqueue.

This read only affects the decision to abort optimistic spinning; stale
values do not affect queue linkage or lock correctness. Use READ_ONCE()
to mark the shared read and match the concurrent WRITE_ONCE() update.

No functional change intended.

Signed-off-by: Yu Peng <pengyu@xxxxxxxxxx>
---
 kernel/locking/osq_lock.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c
index b4233dc2c2b04..db4545e7bb72c 100644
--- a/kernel/locking/osq_lock.c
+++ b/kernel/locking/osq_lock.c
@@ -144,7 +144,7 @@ bool osq_lock(struct optimistic_spin_queue *lock)
 	 * polling, be careful.
 	 */
 	if (smp_cond_load_relaxed(&node->locked, VAL || need_resched() ||
-				  vcpu_is_preempted(node_cpu(node->prev))))
+				  vcpu_is_preempted(node_cpu(READ_ONCE(node->prev)))))
 		return true;
 
 	/* unqueue */
-- 
2.43.0