rxrpc: Don't need to take the RCU read lock in the packet receiver

We don't need to take the RCU read lock in the rxrpc packet receive
function because it's held further up the stack in the IP input routine
around the UDP receive routines.

Fix this by dropping the RCU read lock calls from rxrpc_input_packet().
This simplifies the code.

Fixes: 70790dbe ("rxrpc: Pass the last Tx packet marker in the annotation buffer")
Signed-off-by: David Howells <dhowells@redhat.com>

net/rxrpc/input.c

@@ -1120,6 +1120,8 @@ int rxrpc_extract_header(struct rxrpc_skb_priv *sp, struct sk_buff *skb)
  * The socket is locked by the caller and this prevents the socket from being
  * shut down and the local endpoint from going away, thus sk_user_data will not
  * be cleared until this function returns.
+ *
+ * Called with the RCU read lock held from the IP layer via UDP.
  */
 int rxrpc_input_packet(struct sock *udp_sk, struct sk_buff *skb)
 {
@@ -1215,8 +1217,6 @@ int rxrpc_input_packet(struct sock *udp_sk, struct sk_buff *skb)
 	if (sp->hdr.serviceId == 0)
 		goto bad_message;
 
-	rcu_read_lock();
-
 	if (rxrpc_to_server(sp)) {
 		/* Weed out packets to services we're not offering.  Packets
 		 * that would begin a call are explicitly rejected and the rest
@@ -1228,7 +1228,7 @@ int rxrpc_input_packet(struct sock *udp_sk, struct sk_buff *skb)
 			if (sp->hdr.type == RXRPC_PACKET_TYPE_DATA &&
 			    sp->hdr.seq == 1)
 				goto unsupported_service;
-			goto discard_unlock;
+			goto discard;
 		}
 	}
 
@@ -1248,7 +1248,7 @@ int rxrpc_input_packet(struct sock *udp_sk, struct sk_buff *skb)
 			/* Connection-level packet */
 			_debug("CONN %p {%d}", conn, conn->debug_id);
 			rxrpc_post_packet_to_conn(conn, skb);
-			goto out_unlock;
+			goto out;
 		}
 
 		/* Note the serial number skew here */
@@ -1267,19 +1267,19 @@ int rxrpc_input_packet(struct sock *udp_sk, struct sk_buff *skb)
 
 		/* Ignore really old calls */
 		if (sp->hdr.callNumber < chan->last_call)
-			goto discard_unlock;
+			goto discard;
 
 		if (sp->hdr.callNumber == chan->last_call) {
 			if (chan->call ||
 			    sp->hdr.type == RXRPC_PACKET_TYPE_ABORT)
-				goto discard_unlock;
+				goto discard;
 
 			/* For the previous service call, if completed
 			 * successfully, we discard all further packets.
 			 */
 			if (rxrpc_conn_is_service(conn) &&
 			    chan->last_type == RXRPC_PACKET_TYPE_ACK)
-				goto discard_unlock;
+				goto discard;
 
 			/* But otherwise we need to retransmit the final packet
 			 * from data cached in the connection record.
@@ -1290,16 +1290,14 @@ int rxrpc_input_packet(struct sock *udp_sk, struct sk_buff *skb)
 						    sp->hdr.serial,
 						    sp->hdr.flags, 0);
 			rxrpc_post_packet_to_conn(conn, skb);
-			goto out_unlock;
+			goto out;
 		}
 
 		call = rcu_dereference(chan->call);
 
 		if (sp->hdr.callNumber > chan->call_id) {
-			if (rxrpc_to_client(sp)) {
-				rcu_read_unlock();
+			if (rxrpc_to_client(sp))
 				goto reject_packet;
-			}
 			if (call)
 				rxrpc_input_implicit_end_call(conn, call);
 			call = NULL;
@@ -1318,55 +1316,42 @@ int rxrpc_input_packet(struct sock *udp_sk, struct sk_buff *skb)
 	if (!call || atomic_read(&call->usage) == 0) {
 		if (rxrpc_to_client(sp) ||
 		    sp->hdr.type != RXRPC_PACKET_TYPE_DATA)
-			goto bad_message_unlock;
+			goto bad_message;
 		if (sp->hdr.seq != 1)
-			goto discard_unlock;
+			goto discard;
 		call = rxrpc_new_incoming_call(local, rx, peer, conn, skb);
-		if (!call) {
-			rcu_read_unlock();
+		if (!call)
 			goto reject_packet;
-		}
 		rxrpc_send_ping(call, skb, skew);
 		mutex_unlock(&call->user_mutex);
 	}
 
 	rxrpc_input_call_packet(call, skb, skew);
-	goto discard_unlock;
+	goto discard;
 
-discard_unlock:
-	rcu_read_unlock();
 discard:
 	rxrpc_free_skb(skb, rxrpc_skb_rx_freed);
 out:
 	trace_rxrpc_rx_done(0, 0);
 	return 0;
 
-out_unlock:
-	rcu_read_unlock();
-	goto out;
-
 wrong_security:
-	rcu_read_unlock();
 	trace_rxrpc_abort(0, "SEC", sp->hdr.cid, sp->hdr.callNumber, sp->hdr.seq,
 			  RXKADINCONSISTENCY, EBADMSG);
 	skb->priority = RXKADINCONSISTENCY;
 	goto post_abort;
 
 unsupported_service:
-	rcu_read_unlock();
 	trace_rxrpc_abort(0, "INV", sp->hdr.cid, sp->hdr.callNumber, sp->hdr.seq,
 			  RX_INVALID_OPERATION, EOPNOTSUPP);
 	skb->priority = RX_INVALID_OPERATION;
 	goto post_abort;
 
 reupgrade:
-	rcu_read_unlock();
 	trace_rxrpc_abort(0, "UPG", sp->hdr.cid, sp->hdr.callNumber, sp->hdr.seq,
 			  RX_PROTOCOL_ERROR, EBADMSG);
 	goto protocol_error;
 
-bad_message_unlock:
-	rcu_read_unlock();
 bad_message:
 	trace_rxrpc_abort(0, "BAD", sp->hdr.cid, sp->hdr.callNumber, sp->hdr.seq,
 			  RX_PROTOCOL_ERROR, EBADMSG);