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Sender: Guenter Roeck <groeck7@gmail.com>
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Date:   Wed, 9 Aug 2023 14:45:44 -0700
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Subject: Re: [PATCH 5.15 00/92] 5.15.126-rc1 review
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To:     Joel Fernandes <joel@joelfernandes.org>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, patches@lists.linux.dev,
        linux-kernel@vger.kernel.org, torvalds@linux-foundation.org,
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        paulmck@kernel.org
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From:   Guenter Roeck <linux@roeck-us.net>
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On 8/9/23 13:39, Joel Fernandes wrote:
> On Wed, Aug 9, 2023 at 4:38 PM Guenter Roeck <linux@roeck-us.net> wrote:
>>
>> 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@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, 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".
> 
> Yeah that was weird. Here it is again: https://pastebin.com/raw/L3nv1kH2

I found a couple of crash reports from chromeos-5.10, one of them complaining
about RCU issues. I sent you links via IM. Nothing from 5.15 or later, though.

Guenter