From patchwork series 421422

https://patchwork.ozlabs.org//project/linuxppc-dev/list/?series=421422

arch/powerpc/lib/qspinlock.c

@@ -697,7 +697,15 @@ static __always_inline void queued_spin_lock_mcs_queue(struct qspinlock *lock, b
 	}
 
 release:
-	qnodesp->count--; /* release the node */
+	/*
+	 * Clear the lock before releasing the node, as another CPU might see stale
+	 * values if an interrupt occurs after we increment qnodesp->count
+	 * but before node->lock is initialized. The barrier ensures that
+	 * there are no further stores to the node after it has been released.
+	 */
+	node->lock = NULL;
+	barrier();
+	qnodesp->count--;
 }
 
 void queued_spin_lock_slowpath(struct qspinlock *lock)