SUNRPC: Add barriers to ensure read ordering in rpc_wake_up_task_queue_locked (1166fde6) · Commits · 戴 / test

We need to be careful when testing task->tk_waitqueue in rpc_wake_up_task_queue_locked, because it can be changed while we are holding the queue->lock. By adding appropriate memory barriers, we can ensure that it is safe to test task->tk_waitqueue for equality if the RPC_TASK_QUEUED bit is set. Signed-off-by:

Trond Myklebust <Trond.Myklebust@netapp.com> Cc: stable@vger.kernel.org

net/sunrpc/sched.c

+7 −2

Original line number	Diff line number	Diff line
		@@ -180,6 +180,8 @@ static void __rpc_add_wait_queue(struct rpc_wait_queue *queue,
		list_add_tail(&task->u.tk_wait.list, &queue->tasks[0]);
		task->tk_waitqueue = queue;
		queue->qlen++;
		/* barrier matches the read in rpc_wake_up_task_queue_locked() */
		smp_wmb();
		rpc_set_queued(task);

		dprintk("RPC: %5u added to queue %p \"%s\"\n",
		@@ -430,9 +432,12 @@ static void __rpc_do_wake_up_task(struct rpc_wait_queue *queue, struct rpc_task
		*/
		static void rpc_wake_up_task_queue_locked(struct rpc_wait_queue queue, struct rpc_task task)
		{
		if (RPC_IS_QUEUED(task) && task->tk_waitqueue == queue)
		if (RPC_IS_QUEUED(task)) {
		smp_rmb();
		if (task->tk_waitqueue == queue)
		__rpc_do_wake_up_task(queue, task);
		}
		}

		/*
		* Tests whether rpc queue is empty

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