On Wed, Mar 7, 2018 at 12:19 PM, Neal Cardwell <ncardw...@google.com> wrote:
> On Wed, Mar 7, 2018 at 7:59 AM, Ilpo Järvinen <ilpo.jarvi...@helsinki.fi> 
> wrote:
> > A bogus undo may/will trigger when the loss recovery state is
> > kept until snd_una is above high_seq. If tcp_any_retrans_done
> > is zero, retrans_stamp is cleared in this transient state. On
> > the next ACK, tcp_try_undo_recovery again executes and
> > tcp_may_undo will always return true because tcp_packet_delayed
> > has this condition:
> >     return !tp->retrans_stamp || ...
> >
> > Check for the false fast retransmit transient condition in
> > tcp_packet_delayed to avoid bogus undos. Since snd_una may have
> > advanced on this ACK but CA state still remains unchanged,
> > prior_snd_una needs to be passed instead of tp->snd_una.
> This one also seems like a case where it would be nice to have a
> specific packet-by-packet example, or trace, or packetdrill scenario.
> Something that we might be able to translate into a test, or at least
> to document the issue more explicitly.
I am hesitate for further logic to make undo "perfect" on non-sack
cases b/c undo is very complicated and SACK is extremely
well-supported today. so a trace to demonstrate how severe this issue
is appreciated.

> Thanks!
> neal

Reply via email to