rxrpc: Fix overwaking on call poking

If an rxrpc call is given a poke, it will get woken up unconditionally,
even if there's already a poke pending (for which there will have been a
wake) or if the call refcount has gone to 0.

Fix this by only waking the call if it is still referenced and if it
doesn't already have a poke pending.

Fixes: 15f661dc ("rxrpc: Implement a mechanism to send an event notification to a call")
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org

net/rxrpc/call_object.c

@@ -54,12 +54,14 @@ void rxrpc_poke_call(struct rxrpc_call *call, enum rxrpc_call_poke_trace what)
 		spin_lock_bh(&local->lock);
 		busy = !list_empty(&call->attend_link);
 		trace_rxrpc_poke_call(call, busy, what);
+		if (!busy && !rxrpc_try_get_call(call, rxrpc_call_get_poke))
+			busy = true;
 		if (!busy) {
-			rxrpc_get_call(call, rxrpc_call_get_poke);
 			list_add_tail(&call->attend_link, &local->call_attend_q);
 		}
 		spin_unlock_bh(&local->lock);
-		rxrpc_wake_up_io_thread(local);
+		if (!busy)
+			rxrpc_wake_up_io_thread(local);
 	}
 }