SUNRPC: Signalled ASYNC tasks need to exit

Ensure that signalled ASYNC rpc_tasks exit immediately instead of
spinning until a timeout (or forever).

To avoid checking for the signal flag on every scheduler iteration,
the check is instead introduced in the client's finite state
machine.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Fixes: ae67bd38 ("SUNRPC: Fix up task signalling")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

net/sunrpc/clnt.c

@@ -2433,6 +2433,11 @@ rpc_check_timeout(struct rpc_task *task)
 {
 	struct rpc_clnt	*clnt = task->tk_client;
 
+	if (RPC_SIGNALLED(task)) {
+		rpc_call_rpcerror(task, -ERESTARTSYS);
+		return;
+	}
+
 	if (xprt_adjust_timeout(task->tk_rqstp) == 0)
 		return;