SUNRPC: Prevent an rpc_task wakeup race
The lockless RPC_IS_QUEUED() test in __rpc_execute means that we need to be careful about ordering the calls to rpc_test_and_set_running(task) and rpc_clear_queued(task). If we get the order wrong, then we may end up testing the RPC_TASK_RUNNING flag after __rpc_execute() has looped and changed the state of the rpc_task. Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com> Cc: stable@vger.kernel.org
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@ -324,11 +324,17 @@ EXPORT_SYMBOL_GPL(__rpc_wait_for_completion_task);
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* Note: If the task is ASYNC, and is being made runnable after sitting on an
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* rpc_wait_queue, this must be called with the queue spinlock held to protect
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* the wait queue operation.
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* Note the ordering of rpc_test_and_set_running() and rpc_clear_queued(),
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* which is needed to ensure that __rpc_execute() doesn't loop (due to the
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* lockless RPC_IS_QUEUED() test) before we've had a chance to test
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* the RPC_TASK_RUNNING flag.
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*/
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static void rpc_make_runnable(struct rpc_task *task)
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{
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bool need_wakeup = !rpc_test_and_set_running(task);
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rpc_clear_queued(task);
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if (rpc_test_and_set_running(task))
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if (!need_wakeup)
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return;
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if (RPC_IS_ASYNC(task)) {
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INIT_WORK(&task->u.tk_work, rpc_async_schedule);
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