On Wed, Jan 6, 2016 at 10:19 AM, Yuchung Cheng <ych...@google.com> wrote: > 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. Could you turn off ecn (sysctl net.ipv4.tcp_ecn=0) to see if this still happen?
> >> >> >> 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
