On Wed, May 08, 2019 at 01:56:05PM +0200, Olivier Houchard wrote:
> > > One of processes stuck in infinite loop, admin socket is not responsive so
> > > I've got information only from gdb:
> > > 
> > > 0x0000000000484ab8 in h2_process_mux (h2c=0x2e8ff30) at src/mux_h2.c:2589
> > > 2589            if (h2s->send_wait->events & SUB_CALL_UNSUBSCRIBE)
> > > (gdb) n
> > (...)
> > 
> > CCing Olivier. Olivier, I'm wondering if this is not directly related to
> > what you addressed with this fix merged in 2.0 but not backported :
> > 
> >   998410a ("BUG/MEDIUM: h2: Revamp the way send subscriptions works.")
> > 
> > From what I'm seeing there's no error, the stream is in the sending list,
> > there's no blocking flag, well, everything looks OK, but we're looping
> > on SUB_CALL_UNSUBSCRIBE which apprently should not if I understand it
> > right. Do you think we should backport this patch ?
> > 
> > Remaining of the trace below for reference.
> > 
> > THanks,
> > Willy
> > 
> 
> I can't seem to remember :)

Given the number of bugs we've dealt with in the last few weeks, you're
forgiven :-)

> I remember a bug involving the h2s being added to the send_list twice, and
> thus leading to an infinite loop when parsing the send_list, but it was
> fixed by 9a0f559676c4d309edbe42ba33197e7dd8935f1c, and backported.
> For me, this one was mostly to make me happier about the code, and stop
> abusing SUB_CALL_UNSUBSCRIBE, and if I didn't mention it should be backported
> it's probably I considered the code in 1.9 was OK (or I just forgot), but
> it's still flagged as "BUG" too (but that could be me having "BUG/MEDIUM"
> hardcoded in my finger).
> I think that patch is safe to backport anyway, but I wouldn't swear it solves
> Maciej's issue.

OK. I'll take it then so that we can study the situation under better
conditions if the problem happens again. It may be possible that we've
also overlooked other situations where this infinite loop could happen
with SUB_CALL_UNSUBSCRIBE and that were addressed by your patch.

Thanks,
Willy

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