Re: Repeatable hard lockup running strace testsuite on 4.19.98+ onwards

[Steve McIntyre <steve@einval.com>]

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Hi again,

On Fri, Jun 26, 2020 at 05:50:00PM +0100, Steve McIntyre wrote:
>On Fri, Jun 26, 2020 at 04:25:59PM +0200, Jann Horn wrote:
>>On Fri, Jun 26, 2020 at 3:41 PM Greg KH <gregkh@linuxfoundation.org> wrote:
>>> On Fri, Jun 26, 2020 at 12:35:58PM +0100, Steve McIntyre wrote:
>
>...
>
>>> > Considering I'm running strace build tests to provoke this bug,
>>> > finding the failure in a commit talking about ptrace changes does look
>>> > very suspicious...!
>>> >
>>> > Annoyingly, I can't reproduce this on my disparate other machines
>>> > here, suggesting it's maybe(?) timing related.
>>
>>Does "hard lockup" mean that the HARDLOCKUP_DETECTOR infrastructure
>>prints a warning to dmesg? If so, can you share that warning?
>
>I mean the machine locks hard - X stops updating, the mouse/keyboard
>stop responding. No pings, etc. When I reboot, there's nothing in the
>logs.
>
>>If you don't have any way to see console output, and you don't have a
>>working serial console setup or such, you may want to try re-running
>>those tests while the kernel is booted with netconsole enabled to log
>>to a different machine over UDP (see
>>https://www.kernel.org/doc/Documentation/networking/netconsole.txt).
>
>ACK, will try that now for you.
>
>>You may want to try setting the sysctl kernel.sysrq=1 , then when the
>>system has locked up, press ALT+PRINT+L (to generate stack traces for
>>all active CPUs from NMI context), and maybe also ALT+PRINT+T and
>>ALT+PRINT+W (to collect more information about active tasks).
>
>Nod.
>
>>(If you share stack traces from these things with us, it would be
>>helpful if you could run them through scripts/decode_stacktrace.pl
>>from the kernel tree first, to add line number information.)
>
>ACK.

Output passed through scripts/decode_stacktrace.sh attached.

Just about to try John's suggestion next.

-- 
Steve McIntyre, Cambridge, UK.                                steve@einval.com
Dance like no one's watching. Encrypt like everyone is.
 - @torproject

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