SUNRPC: Ensure we always run the tk_callback before tk_action

This fixes a race in which the task->tk_callback() puts the rpc_task
to sleep, setting a new callback. Under certain circumstances, the current
code may end up executing the task->tk_action before it gets round to the
callback.
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Cc: stable@kernel.org

net/sunrpc/sched.c

@@ -630,14 +630,12 @@ static void __rpc_execute(struct rpc_task *task)
 			save_callback = task->tk_callback;
 			task->tk_callback = NULL;
 			save_callback(task);
-		}
-
+		} else {
 			/*
 			 * Perform the next FSM step.
 			 * tk_action may be NULL when the task has been killed
 			 * by someone else.
 			 */
-		if (!RPC_IS_QUEUED(task)) {
 			if (task->tk_action == NULL)
 				break;
 			task->tk_action(task);