On Wed, Jan 6, 2016 at 8:50 AM, Oleksandr Natalenko <oleksa...@natalenko.name> wrote: > > Unfortunately, the patch didn't help -- I've got the same stacktrace with > slightly different offset (+3) within the function. > > Now trying to get full stacktrace via netconsole. Need more time. > > Meanwhile, any other ideas on what went wrong?
That's odd b/c the patch already checks and avoids div0. Can post me the stacktrace and kernel warnings if any ... One possibility is that tcp_cwnd_reduction() may set a cwnd of 0, which then gets used to start another recovery phase. This may or may not be the culprit of this div0 issue because I wasn't able to reproduce exactly your issue on our servers. But I will post the fix today and CC you. > > > On December 22, 2015 4:10:32 AM EET, Yuchung Cheng <ych...@google.com> wrote: > >On Mon, Dec 21, 2015 at 12:25 PM, Oleksandr Natalenko > ><oleksa...@natalenko.name> wrote: > >> Commit 3759824da87b30ce7a35b4873b62b0ba38905ef5 (tcp: PRR uses CRB > >mode by > >> default and SS mode conditionally) introduced changes to > >net/ipv4/tcp_input.c > >> tcp_cwnd_reduction() that, possibly, cause division by zero, and > >therefore, > >> kernel panic in interrupt handler [1]. > >> > >> Reverting 3759824da87b30ce7a35b4873b62b0ba38905ef5 seems to fix the > >issue. > >> > >> I'm able to reproduce the issue on 4.3.0–4.3.3 once per several day > >> (occasionally). > >> > >> What could be done to help in debugging this issue? > >Do you have ECN enabled (i.e. sysctl net.ipv4.tcp_ecn > 0)? > > > >If so I suspect an ACK carrying ECE during CA_Loss causes entering CWR > >state w/o calling tcp_init_cwnd_reduct() to set tp->prior_cwnd. Can > >you try this debug / quick-fix patch and send me the error message if > >any? > > > > > >> > >> Regards, > >> Oleksandr. > >> > >> [1] http://i.piccy.info/ > >> > >i9/6f5cb187c4ff282d189f78c63f95af43/1450729403/283985/951663/panic.jpg > > -- > Sent from my Android device with K-9 Mail. Please excuse my brevity. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
