Re: [PATCH 5.15 00/92] 5.15.126-rc1 review

[Guenter Roeck]

On 8/9/23 13:14, Joel Fernandes wrote:
> On Wed, Aug 09, 2023 at 12:25:48PM -0700, Guenter Roeck wrote:
> > On Wed, Aug 09, 2023 at 02:35:59PM -0400, Joel Fernandes wrote:
> > > On Wed, Aug 9, 2023 at 12:18 PM Guenter Roeck <linux@xxxxxxxxxxxx> 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, please
> > > > > > 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 scenarios
> > > > > 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. The
> > > > > 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.
> >
> > Hmm, we do see lots of soft lockups with multi_cpu_stop() in the backtrace,
> > but not with v5.15.y but with v5.4.y. The actual hang is in stop_machine_yield().
>
> Interesting. It looks similar as far as the stack dump in gdb goes, here are
> the stacks I dumped with the hang I referred to:
> https://paste.debian.net/1288308/

That link gives me "Entry not found".

Guenter