Re: [Regression] stress-ng udp-flood causes kernel panic on Ampere Altra #forregzbot

[Thorsten Leemhuis <regressions@leemhuis.info>]

[TLDR: I'm adding this regression report to the list of tracked
regressions; all text from me you find below is based on a few templates
paragraphs you might have encountered already already in similar form.]

TWIMC: this mail is primarily send for documentation purposes and for
regzbot, my Linux kernel regression tracking bot. These mails usually
contain '#forregzbot' in the subject, to make them easy to spot and filter.

Hi, this is your Linux kernel regression tracker.

On 01.07.22 13:11, Kajetan Puchalski wrote:
> Hi,
> 
> While running the udp-flood test from stress-ng on Ampere Altra (Mt.
> Jade platform) I encountered a kernel panic caused by NULL pointer
> dereference within nf_conntrack.
> 
> The issue is present in the latest mainline (5.19-rc4), latest stable
> (5.18.8), as well as multiple older stable versions. The last working
> stable version I found was 5.15.40.
> 
> Through bisecting I've traced the issue back to mainline commit
> 719774377622bc4025d2a74f551b5dc2158c6c30 (netfilter: conntrack: convert to refcount_t api),
> on kernels from before this commit the test runs fine. As far as I can tell, this commit was
> included in stable with version 5.15.41, thus causing the regression
> compared to 5.15.40. It was included in the mainline with version 5.16.

FWIW, looks like it was merged for v5.17-rc1
$ git describe --contains --tags  719774377622bc4025

v5.17-rc1~170^2~24^2~19

> The issue is very consistently reproducible as well, running this
> command resulted in the same kernel panic every time I tried it on
> different kernels from after the change in question was merged.
> 
> stress-ng --udp-flood 0 -t 1m --metrics-brief --perf
> 
> The commit was not easily revertible so I can't say whether reverting it
> on the latest mainline would fix the problem or not.
> 
> [...]
> 
> The distirbution is Ubuntu 20.04.3 LTS, the architecture is aarch64.
> 
> Please let me know if I can provide any more details or try any more
> tests.

Thanks for the report. To be sure below issue doesn't fall through the
cracks unnoticed, I'm adding it to regzbot, my Linux kernel regression
tracking bot:

#regzbot ^introduced 719774377622bc402
#regzbot title net: netfilter: stress-ng udp-flood causes kernel panic
on Ampere Altra

This isn't a regression? This issue or a fix for it are already
discussed somewhere else? It was fixed already? You want to clarify when
the regression started to happen? Or point out I got the title or
something else totally wrong? Then just reply -- ideally with also
telling regzbot about it, as explained here:
https://linux-regtracking.leemhuis.info/tracked-regression/

Reminder for developers: When fixing the issue, add 'Link:' tags
pointing to the report (the mail this one replies to), as explained for
in the Linux kernel's documentation; above webpage explains why this is
important for tracked regressions.

Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)

P.S.: As the Linux kernel's regression tracker I deal with a lot of
reports and sometimes miss something important when writing mails like
this. If that's the case here, don't hesitate to tell me in a public
reply, it's in everyone's interest to set the public record straight.