rxrpc: Fix trace-after-put looking at the put connection record

rxrpc_put_*conn() calls trace_rxrpc_conn() after they have done the
decrement of the refcount - which looks at the debug_id in the connection
record.  But unless the refcount was reduced to zero, we no longer have the
right to look in the record and, indeed, it may be deleted by some other
thread.

Fix this by getting the debug_id out before decrementing the refcount and
then passing that into the tracepoint.

Fixes: 363deeab ("rxrpc: Add connection tracepoint and client conn state tracepoint")
Signed-off-by: David Howells <dhowells@redhat.com>

include/trace/events/rxrpc.h

@@ -546,10 +546,10 @@ TRACE_EVENT(rxrpc_peer,
 	    );
 
 TRACE_EVENT(rxrpc_conn,
-	    TP_PROTO(struct rxrpc_connection *conn, enum rxrpc_conn_trace op,
+	    TP_PROTO(unsigned int conn_debug_id, enum rxrpc_conn_trace op,
 		     int usage, const void *where),
 
-	    TP_ARGS(conn, op, usage, where),
+	    TP_ARGS(conn_debug_id, op, usage, where),
 
 	    TP_STRUCT__entry(
 		    __field(unsigned int,	conn		)
@@ -559,7 +559,7 @@ TRACE_EVENT(rxrpc_conn,
 			     ),
 
 	    TP_fast_assign(
-		    __entry->conn = conn->debug_id;
+		    __entry->conn = conn_debug_id;
 		    __entry->op = op;
 		    __entry->usage = usage;
 		    __entry->where = where;

net/rxrpc/call_accept.c

@@ -84,7 +84,7 @@ static int rxrpc_service_prealloc_one(struct rxrpc_sock *rx,
 		smp_store_release(&b->conn_backlog_head,
 				  (head + 1) & (size - 1));
 
-		trace_rxrpc_conn(conn, rxrpc_conn_new_service,
+		trace_rxrpc_conn(conn->debug_id, rxrpc_conn_new_service,
 				 atomic_read(&conn->usage), here);
 	}
 

net/rxrpc/conn_client.c

@@ -212,7 +212,8 @@ rxrpc_alloc_client_connection(struct rxrpc_conn_parameters *cp, gfp_t gfp)
 	rxrpc_get_local(conn->params.local);
 	key_get(conn->params.key);
 
-	trace_rxrpc_conn(conn, rxrpc_conn_new_client, atomic_read(&conn->usage),
+	trace_rxrpc_conn(conn->debug_id, rxrpc_conn_new_client,
+			 atomic_read(&conn->usage),
 			 __builtin_return_address(0));
 	trace_rxrpc_client(conn, -1, rxrpc_client_alloc);
 	_leave(" = %p", conn);
@@ -985,11 +986,12 @@ rxrpc_put_one_client_conn(struct rxrpc_connection *conn)
 void rxrpc_put_client_conn(struct rxrpc_connection *conn)
 {
 	const void *here = __builtin_return_address(0);
+	unsigned int debug_id = conn->debug_id;
 	int n;
 
 	do {
 		n = atomic_dec_return(&conn->usage);
-		trace_rxrpc_conn(conn, rxrpc_conn_put_client, n, here);
+		trace_rxrpc_conn(debug_id, rxrpc_conn_put_client, n, here);
 		if (n > 0)
 			return;
 		ASSERTCMP(n, >=, 0);

net/rxrpc/conn_object.c

@@ -269,7 +269,7 @@ bool rxrpc_queue_conn(struct rxrpc_connection *conn)
 	if (n == 0)
 		return false;
 	if (rxrpc_queue_work(&conn->processor))
-		trace_rxrpc_conn(conn, rxrpc_conn_queued, n + 1, here);
+		trace_rxrpc_conn(conn->debug_id, rxrpc_conn_queued, n + 1, here);
 	else
 		rxrpc_put_connection(conn);
 	return true;
@@ -284,7 +284,7 @@ void rxrpc_see_connection(struct rxrpc_connection *conn)
 	if (conn) {
 		int n = atomic_read(&conn->usage);
 
-		trace_rxrpc_conn(conn, rxrpc_conn_seen, n, here);
+		trace_rxrpc_conn(conn->debug_id, rxrpc_conn_seen, n, here);
 	}
 }
 
@@ -296,7 +296,7 @@ void rxrpc_get_connection(struct rxrpc_connection *conn)
 	const void *here = __builtin_return_address(0);
 	int n = atomic_inc_return(&conn->usage);
 
-	trace_rxrpc_conn(conn, rxrpc_conn_got, n, here);
+	trace_rxrpc_conn(conn->debug_id, rxrpc_conn_got, n, here);
 }
 
 /*
@@ -310,7 +310,7 @@ rxrpc_get_connection_maybe(struct rxrpc_connection *conn)
 	if (conn) {
 		int n = atomic_fetch_add_unless(&conn->usage, 1, 0);
 		if (n > 0)
-			trace_rxrpc_conn(conn, rxrpc_conn_got, n + 1, here);
+			trace_rxrpc_conn(conn->debug_id, rxrpc_conn_got, n + 1, here);
 		else
 			conn = NULL;
 	}
@@ -333,10 +333,11 @@ static void rxrpc_set_service_reap_timer(struct rxrpc_net *rxnet,
 void rxrpc_put_service_conn(struct rxrpc_connection *conn)
 {
 	const void *here = __builtin_return_address(0);
+	unsigned int debug_id = conn->debug_id;
 	int n;
 
 	n = atomic_dec_return(&conn->usage);
-	trace_rxrpc_conn(conn, rxrpc_conn_put_service, n, here);
+	trace_rxrpc_conn(debug_id, rxrpc_conn_put_service, n, here);
 	ASSERTCMP(n, >=, 0);
 	if (n == 1)
 		rxrpc_set_service_reap_timer(conn->params.local->rxnet,
@@ -420,7 +421,7 @@ void rxrpc_service_connection_reaper(struct work_struct *work)
 		 */
 		if (atomic_cmpxchg(&conn->usage, 1, 0) != 1)
 			continue;
-		trace_rxrpc_conn(conn, rxrpc_conn_reap_service, 0, NULL);
+		trace_rxrpc_conn(conn->debug_id, rxrpc_conn_reap_service, 0, NULL);
 
 		if (rxrpc_conn_is_client(conn))
 			BUG();

net/rxrpc/conn_service.c

@@ -134,7 +134,7 @@ struct rxrpc_connection *rxrpc_prealloc_service_connection(struct rxrpc_net *rxn
 		list_add_tail(&conn->proc_link, &rxnet->conn_proc_list);
 		write_unlock(&rxnet->conn_lock);
 
-		trace_rxrpc_conn(conn, rxrpc_conn_new_service,
+		trace_rxrpc_conn(conn->debug_id, rxrpc_conn_new_service,
 				 atomic_read(&conn->usage),
 				 __builtin_return_address(0));
 	}