[net 1/1] tipc: remove joining group member from congested list

[net 1/1] tipc: remove joining group member from congested list

[Jon Maloy]

When we receive a JOIN message from a peer member, the message may
contain an advertised window value ADV_IDLE that permits removing the
member in question from the tipc_group::congested list. However, since
the removal has been made conditional on that the advertised window is
*not* ADV_IDLE, we miss this case. This has the effect that a sender
sometimes may enter a state of permanent, false, broadcast congestion.

We fix this by unconditinally removing the member from the congested
list before calling tipc_member_update(), which might potentially sort
it into the list again.

Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
---
 net/tipc/group.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/net/tipc/group.c b/net/tipc/group.c
index bbc004e..7ebbdeb 100644
--- a/net/tipc/group.c
+++ b/net/tipc/group.c
@@ -689,10 +689,8 @@ void tipc_group_proto_rcv(struct tipc_group *grp, bool *usr_wakeup,
 			msg_set_grp_bc_seqno(ehdr, m->bc_syncpt);
 			__skb_queue_tail(inputq, m->event_msg);
 		}
-		if (m->window < ADV_IDLE)
-			tipc_group_update_member(m, 0);
-		else
-			list_del_init(&m->congested);
+		list_del_init(&m->congested);
+		tipc_group_update_member(m, 0);
 		return;
 	case GRP_LEAVE_MSG:
 		if (!m)
-- 
2.1.4

Re: [net 1/1] tipc: remove joining group member from congested list

[David Miller]

From: Jon Maloy <jon.maloy@ericsson.com>
Date: Wed, 20 Dec 2017 11:03:15 +0100

> When we receive a JOIN message from a peer member, the message may
> contain an advertised window value ADV_IDLE that permits removing the
> member in question from the tipc_group::congested list. However, since
> the removal has been made conditional on that the advertised window is
> *not* ADV_IDLE, we miss this case. This has the effect that a sender
> sometimes may enter a state of permanent, false, broadcast congestion.
> 
> We fix this by unconditinally removing the member from the congested
> list before calling tipc_member_update(), which might potentially sort
> it into the list again.
> 
> Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>

I bet this bug wasn't fun to track down.

Applied, thanks Jon.