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

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Date:   Thu, 10 Aug 2023 19:13:14 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     "Paul E. McKenney" <paulmck@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, patches@...ts.linux.dev,
        linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
        akpm@...ux-foundation.org, shuah@...nel.org, patches@...nelci.org,
        lkft-triage@...ts.linaro.org, pavel@...x.de, jonathanh@...dia.com,
        f.fainelli@...il.com, sudipm.mukherjee@...il.com,
        srw@...dewatkins.net, rwarsow@....de, conor@...nel.org
Subject: Re: [PATCH 5.15 00/92] 5.15.126-rc1 review



> On Aug 10, 2023, at 6:55 PM, Guenter Roeck <linux@...ck-us.net> wrote:
> 
> On 8/10/23 14:54, Joel Fernandes wrote:
>>> On Thu, Aug 10, 2023 at 10:55:16AM -0700, Paul E. McKenney wrote:
>>> On Wed, Aug 09, 2023 at 02:45:44PM -0700, Guenter Roeck wrote:
>>>> On 8/9/23 13:39, Joel Fernandes wrote:
>>>>> On Wed, Aug 9, 2023 at 4:38 PM Guenter Roeck <linux@...ck-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@...ck-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.
>>> 
>>> Is the crash showing the eternally refiring timer fixed by this commit?
>>> 
>>> 53e87e3cdc15 ("timers/nohz: Last resort update jiffies on nohz_full IRQ entry")
>> Ah I was just replying, I have been seeing really good results after applying
>> the following 3 commits since yesterday:
>> 53e87e3cdc15 ("timers/nohz: Last resort update jiffies on nohz_full IRQ entry")
>> 5417ddc1cf1f ("timers/nohz: Switch to ONESHOT_STOPPED in the low-res handler when the tick is stopped")
>> a1ff03cd6fb9 ("tick: Detect and fix jiffies update stall")
> 
> Would those also apply to v5.10.y, or just 5.15.y ?

All apply to 5.10 but one. I am currently testing with it more and will post to stable for 5.10 as well.

Thanks,

 - Joel



> 
> Thanks,
> Guenter
> 
>> 5417ddc1cf1f also mentioned a "tick storm" which is exactly what I was
>> seeing.
>> I did a lengthy test and everything is looking good. I'll send these out to
>> the stable list.
>> thanks,
>>  - Joel
>