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From:   Joel Fernandes <joel@joelfernandes.org>
Date:   Wed, 9 Aug 2023 14:35:59 -0400
Message-ID: <CAEXW_YQ4GqPwvUF8=8CWmdj=cD56v_eEVK-EirsObQXyBDFVpg@mail.gmail.com>
Subject: Re: [PATCH 5.15 00/92] 5.15.126-rc1 review
To:     Guenter Roeck <linux@roeck-us.net>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, patches@lists.linux.dev,
        linux-kernel@vger.kernel.org, torvalds@linux-foundation.org,
        akpm@linux-foundation.org, shuah@kernel.org, patches@kernelci.org,
        lkft-triage@lists.linaro.org, pavel@denx.de, jonathanh@nvidia.com,
        f.fainelli@gmail.com, sudipm.mukherjee@gmail.com,
        srw@sladewatkins.net, rwarsow@gmx.de, conor@kernel.org,
        paulmck@kernel.org
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On Wed, Aug 9, 2023 at 12:18=E2=80=AFPM Guenter Roeck <linux@roeck-us.net> =
wrote:
>
> On 8/9/23 06:53, Joel Fernandes wrote:
> > On Wed, Aug 09, 2023 at 12:40:36PM +0200, Greg Kroah-Hartman wrote:
> >> This is the start of the stable review cycle for the 5.15.126 release.
> >> There are 92 patches in this series, all will be posted as a response
> >> to this one.  If anyone has any issues with these being applied, pleas=
e
> >> let me know.
> >>
> >> Responses should be made by Fri, 11 Aug 2023 10:36:10 +0000.
> >> Anything received after that time might be too late.
> >>
> >> The whole patch series can be found in one patch at:
> >>      https://www.kernel.org/pub/linux/kernel/v5.x/stable-review/patch-=
5.15.126-rc1.gz
> >> or in the git tree and branch at:
> >>      git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable=
-rc.git linux-5.15.y
> >> and the diffstat can be found below.
> >
> > Not necesscarily new with 5.15 stable but 3 of the 19 rcutorture scenar=
ios
> > hang with this -rc: TREE04, TREE07, TASKS03.
> >
> > 5.15 has a known stop machine issue where it hangs after 1.5 hours with=
 cpu
> > hotplug rcutorture testing. Me and tglx are continuing to debug this. T=
he
> > issue does not show up on anything but 5.15 stable kernels and neither =
on
> > mainline.
> >
>
> Do you by any have a crash pattern that we could possibly use to find the=
 crash
> in ChromeOS crash logs ? No idea if that would help, but it could provide=
 some
> additional data points.

The pattern shows as a hard hang, the system is unresponsive and all CPUs
are stuck in stop_machine. Sometimes it recovers on its own from the
hang and then RCU immediately gives stall warnings. It takes 1.5 hour
to reproduce and sometimes never happens for several hours.

It appears related to CPU hotplug since gdb showed me most of the CPUs
are spinning in multi_cpu_stop() / stop machine after the hang.

thanks,

 - Joel