[PATCH net-next] rxrpc: Make service connection lookup always check for retry

[PATCH net-next] rxrpc: Make service connection lookup always check for retry

[David Howells]

When an RxRPC service packet comes in, the target connection is looked up
by an rb-tree search under RCU and a read-locked seqlock; the seqlock retry
check is, however, currently skipped if we got a match, but probably
shouldn't be in case the connection we found gets replaced whilst we're
doing a search.

Make the lookup procedure always go through need_seqretry(), even if the
lookup was successful.  This makes sure we always pick up on a write-lock
event.

On the other hand, since we don't take a ref on the object, but rely on RCU
to prevent its destruction after dropping the seqlock, I'm not sure this is
necessary.

Signed-off-by: David Howells <dhowells@redhat.com>
---

 net/rxrpc/conn_service.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/net/rxrpc/conn_service.c b/net/rxrpc/conn_service.c
index e60fcd2a4a02..f6fcdb3130a1 100644
--- a/net/rxrpc/conn_service.c
+++ b/net/rxrpc/conn_service.c
@@ -50,12 +50,11 @@ struct rxrpc_connection *rxrpc_find_service_conn_rcu(struct rxrpc_peer *peer,
 			else if (conn->proto.index_key > k.index_key)
 				p = rcu_dereference_raw(p->rb_right);
 			else
-				goto done;
+				break;
 			conn = NULL;
 		}
 	} while (need_seqretry(&peer->service_conn_lock, seq));
 
-done:
 	done_seqretry(&peer->service_conn_lock, seq);
 	_leave(" = %d", conn ? conn->debug_id : -1);
 	return conn;

Re: [PATCH net-next] rxrpc: Make service connection lookup always check for retry

[David Miller]

From: David Howells <dhowells@redhat.com>
Date: Mon, 04 Sep 2017 15:28:28 +0100

> When an RxRPC service packet comes in, the target connection is looked up
> by an rb-tree search under RCU and a read-locked seqlock; the seqlock retry
> check is, however, currently skipped if we got a match, but probably
> shouldn't be in case the connection we found gets replaced whilst we're
> doing a search.
> 
> Make the lookup procedure always go through need_seqretry(), even if the
> lookup was successful.  This makes sure we always pick up on a write-lock
> event.
> 
> On the other hand, since we don't take a ref on the object, but rely on RCU
> to prevent its destruction after dropping the seqlock, I'm not sure this is
> necessary.
> 
> Signed-off-by: David Howells <dhowells@redhat.com>

Applied, thanks David.