On Mon, Aug 24, 2015 at 02:36:59PM -0400, Vlad Yasevich wrote:
> On 08/24/2015 02:31 PM, Marcelo Ricardo Leitner wrote:
> > On Mon, Aug 24, 2015 at 02:13:38PM -0400, Vlad Yasevich wrote:
> >> On 08/23/2015 07:30 AM, Xin Long wrote:
> >>> when A sends a data to B, then A close() and enter into SHUTDOWN_PENDING
> >>> state,
> >>> if B neither claim his rwnd is 0 nor send SACK for this data, A will keep
> >>> retransmitting this data util t5 timeout, Max.Retrans times can't work
> >>> anymore,
> >>> which is bad.
> >>>
> >>> if B's rwnd is not 0, it should send abord after Max.Retrans times, only
> >>> when
> >>> B's rwnd == 0 and A's retransmitting beyonds Max.Retrans times, A will
> >>> start
> >>> t5 timer, which is also commit f8d960524 means, but it lacks the condition
> >>> peer.rwnd == 0.
> >>>
> >>> Fixes: f8d960524 ("sctp: Enforce retransmission limit during shutdown")
> >>> Signed-off-by: Xin Long <lucien....@gmail.com>
> >>> ---
> >>> net/sctp/sm_statefuns.c | 3 ++-
> >>> 1 file changed, 2 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/net/sctp/sm_statefuns.c b/net/sctp/sm_statefuns.c
> >>> index 3ee27b7..deb9eab 100644
> >>> --- a/net/sctp/sm_statefuns.c
> >>> +++ b/net/sctp/sm_statefuns.c
> >>> @@ -5412,7 +5412,8 @@ sctp_disposition_t sctp_sf_do_6_3_3_rtx(struct net
> >>> *net,
> >>> SCTP_INC_STATS(net, SCTP_MIB_T3_RTX_EXPIREDS);
> >>>
> >>> if (asoc->overall_error_count >= asoc->max_retrans) {
> >>> - if (asoc->state == SCTP_STATE_SHUTDOWN_PENDING) {
> >>> + if (!q->asoc->peer.rwnd &&
> >>> + asoc->state == SCTP_STATE_SHUTDOWN_PENDING) {
> >>> /*
> >>> * We are here likely because the receiver had its rwnd
> >>> * closed for a while and we have not been able to
> >>>
> >>
> >> This may not work as expected. peer.rwnd is the calculated peer window,
> >> but it
> >> also gets updated when we receive sacks. So there is no way to tell that
> >> the current windows is 0 because peer told us, or because we sent data to
> >> make 0
> >> and the peer hasn't responded.
> >
> > I'm not sure I follow you, Vlad. I don't think we care on why we have
> > zero-window in there, just that if we are at it on that stage. Either
> > one, if it's zero window, we will go through T5 and give it more time to
> > recover, but if it's not zero window, I don't see a reason to enable T5..
>
> No, these are 2 distinct instances. In one instance, the peer is reachable
> and
> is able to communication 0 rwnd state to us. Thus we are being nice and
> granting
> the peer more time to exit the 0 window state.
>
> In the other state, the peer is unreachable and we just happen to hit the
> 0-window
> condition based on some estimations of the peer window. In this case, we
> should
> be subject to the Max.RTX and terminate the association sooner.
Makes sense, we can do better in there. Thanks Vlad.
Marcelo
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