rxrpc: Fix life check

The life-checking function, which is used by kAFS to make sure that a call
is still live in the event of a pending signal, only samples the received
packet serial number counter; it doesn't actually provoke a change in the
counter, rather relying on the server to happen to give us a packet in the
time window.

Fix this by adding a function to force a ping to be transmitted.

kAFS then keeps track of whether there's been a stall, and if so, uses the
new function to ping the server, resetting the timeout to allow the reply
to come back.

If there's a stall, a ping and the call is *still* stalled in the same
place after another period, then the call will be aborted.

Fixes: bc5e3a546d ("rxrpc: Use MSG_WAITALL to tell sendmsg() to temporarily ignore signals")
Fixes: f4d15fb6f9 ("rxrpc: Provide functions for allowing cleaner handling of signals")
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/trace/events/rxrpc.h

@@ -181,6 +181,7 @@ enum rxrpc_timer_trace {
 enum rxrpc_propose_ack_trace {
 	rxrpc_propose_ack_client_tx_end,
 	rxrpc_propose_ack_input_data,
+	rxrpc_propose_ack_ping_for_check_life,
 	rxrpc_propose_ack_ping_for_keepalive,
 	rxrpc_propose_ack_ping_for_lost_ack,
 	rxrpc_propose_ack_ping_for_lost_reply,
@@ -380,6 +381,7 @@ enum rxrpc_tx_point {
 #define rxrpc_propose_ack_traces \
 	EM(rxrpc_propose_ack_client_tx_end,	"ClTxEnd") \
 	EM(rxrpc_propose_ack_input_data,	"DataIn ") \
+	EM(rxrpc_propose_ack_ping_for_check_life, "ChkLife") \
 	EM(rxrpc_propose_ack_ping_for_keepalive, "KeepAlv") \
 	EM(rxrpc_propose_ack_ping_for_lost_ack,	"LostAck") \
 	EM(rxrpc_propose_ack_ping_for_lost_reply, "LostRpl") \