SUNRPC: Add barriers to ensure read ordering in rpc_wake_up_task_queue_locked
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
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@ -180,6 +180,8 @@ static void __rpc_add_wait_queue(struct rpc_wait_queue *queue,
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list_add_tail(&task->u.tk_wait.list, &queue->tasks[0]);
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task->tk_waitqueue = queue;
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queue->qlen++;
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/* barrier matches the read in rpc_wake_up_task_queue_locked() */
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smp_wmb();
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rpc_set_queued(task);
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dprintk("RPC: %5u added to queue %p \"%s\"\n",
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@ -430,8 +432,11 @@ static void __rpc_do_wake_up_task(struct rpc_wait_queue *queue, struct rpc_task
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*/
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static void rpc_wake_up_task_queue_locked(struct rpc_wait_queue *queue, struct rpc_task *task)
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{
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if (RPC_IS_QUEUED(task) && task->tk_waitqueue == queue)
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__rpc_do_wake_up_task(queue, task);
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if (RPC_IS_QUEUED(task)) {
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smp_rmb();
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if (task->tk_waitqueue == queue)
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__rpc_do_wake_up_task(queue, task);
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}
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}
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/*
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