Re: [net 1/1] tipc: fix problems with multipoint-to-point flow control

[David Miller <davem@davemloft.net>]

From: Jon Maloy <jon.maloy@ericsson.com>
Date: Fri, 29 Dec 2017 19:48:02 +0100

> In commit 04d7b574b245 ("tipc: add multipoint-to-point flow control") we
> introduced a protocol for preventing buffer overflow when many group
> members try to simultaneously send messages to the same receiving member.
> 
> Stress test of this mechanism has revealed a couple of related bugs:
> 
> - When the receiving member receives an advertisement REMIT message from
>   one of the senders, it will sometimes prematurely activate a pending
>   member and send it the remitted advertisement, although the upper
>   limit for active senders has been reached. This leads to accumulation
>   of illegal advertisements, and eventually to messages being dropped
>   because of receive buffer overflow.
> 
> - When the receiving member leaves REMITTED state while a received
>   message is being read, we miss to look at the pending queue, to
>   activate the oldest pending peer. This leads to some pending senders
>   being starved out, and never getting the opportunity to profit from
>   the remitted advertisement.
> 
> We fix the former in the function tipc_group_proto_rcv() by returning
> directly from the function once it becomes clear that the remitting
> peer cannot leave REMITTED state at that point.
> 
> We fix the latter in the function tipc_group_update_rcv_win() by looking
> up and activate the longest pending peer when it becomes clear that the
> remitting peer now can leave REMITTED state.
> 
> Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>

Applied, thanks Jon.