linux-kernel - Re: [PATCH 6.4 000/227] 6.4.7-rc1 review

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Date:   Thu, 27 Jul 2023 07:39:54 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     paulmck@...nel.org, Joel Fernandes <joel@...lfernandes.org>
Cc:     Pavel Machek <pavel@...x.de>,
        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, jonathanh@...dia.com,
        f.fainelli@...il.com, sudipm.mukherjee@...il.com,
        srw@...dewatkins.net, rwarsow@....de, conor@...nel.org,
        rcu@...r.kernel.org
Subject: Re: [PATCH 6.4 000/227] 6.4.7-rc1 review

On 7/27/23 07:06, Paul E. McKenney wrote:
> On Thu, Jul 27, 2023 at 09:26:52AM -0400, Joel Fernandes wrote:
>>
>>
>>> On Jul 27, 2023, at 7:35 AM, Pavel Machek <pavel@...x.de> wrote:
>>>
>>> Hi!
>>>
>>>>> This is the start of the stable review cycle for the 6.4.7 release.
>>>>> There are 227 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 Thu, 27 Jul 2023 10:44:26 +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/v6.x/stable-review/patch-6.4.7-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-6.4.y
>>>>> and the diffstat can be found below.
>>>>
>>>> I saw this when running rcutorture, this one happened in the TREE04
>>>> configuration. This is likely due to the stuttering issues we are discussing
>>>> in the other thread. Anyway I am just making a note here while I am
>>>> continuing to look into it.
>>>
>>> So is the stuttering new in 6.4.7?
>>
>> No it is an old feature in RCU torture tests. But is dependent on timing. Something
>> changed in recent kernels that is making the issues with it more likely. Its hard to bisect as failure sometimes takes hours.
>>
>>>
>>>> Other than that, all tests pass:
>>>> Tested-by: Joel Fernandes (Google) <joel@...lfernandes.org>
>>>
>>> ...or you still believe 6.4.7 is okay to release?
>>
>> As such, it should be Ok. However naturally I am not happy that the RCU testing
>> is intermittently failing. These issues have been seen in last several 6.4 stable releases
>> so since those were released, maybe this one can be too?
>> The fix for stuttering is currently being reviewed.
> 
> Or, to look at it another way, the stuttering fix is specific to torture
> testing.  Would we really want to hold up a -stable release only because
> rcutorture occasionally gives a false-positive failure on certain types
> of systems?
> 

No. However, (unrelated) in linux-next, rcu tests sometimes result in apparent hangs
or long runtime.

[    0.778841] Mount-cache hash table entries: 512 (order: 0, 4096 bytes, linear)
[    0.779011] Mountpoint-cache hash table entries: 512 (order: 0, 4096 bytes, linear)
[    0.797998] Running RCU synchronous self tests
[    0.798209] Running RCU synchronous self tests
[    0.912368] smpboot: CPU0: AMD Opteron 63xx class CPU (family: 0x15, model: 0x2, stepping: 0x0)
[    0.923398] RCU Tasks: Setting shift to 2 and lim to 1 rcu_task_cb_adjust=1.
[    0.925419] Running RCU-tasks wait API self tests

(hangs until aborted). This is primarily with Opteron CPUs, but also with others such as Haswell,
Icelake-Server, and pentium3. It is all but impossible to bisect because it doesn't happen
all the time. All I was able to figure out was that it has to do with rcu changes in linux-next.
I'd be much more concerned about that.

Guenter