linux-kernel - Re: [RFC 0/1] Add sysctl entry for controlling crash_kexec_post

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Date:   Mon, 4 Apr 2022 16:43:34 -0400
From:   Alejandro Jimenez <alejandro.j.jimenez@...cle.com>
To:     "Guilherme G. Piccoli" <gpiccoli@...lia.com>, corbet@....net,
        mcgrof@...nel.org, keescook@...omium.org, yzaikin@...gle.com,
        linux-fsdevel@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     akpm@...ux-foundation.org, linux@...musvillemoes.dk,
        ebiggers@...gle.com, peterz@...radead.org, ying.huang@...el.com,
        mchehab+huawei@...nel.org, Jason@...c4.com, daniel@...earbox.net,
        robh@...nel.org, wangqing@...o.com, prestwoj@...il.com,
        dsahern@...nel.org, stephen.s.brennan@...cle.com
Subject: Re: [RFC 0/1] Add sysctl entry for controlling
 crash_kexec_post_notifiers

Hi Guilherme,

On 4/2/2022 10:01 AM, Guilherme G. Piccoli wrote:
> On 01/04/2022 17:22, Alejandro Jimenez wrote:
>> I noticed that in contrast to other kernel core parameters (e.g. kernel.panic,
>> kernel.panic_on_warn, kernel.panic_print) crash_kexec_post_notifiers is not
>> available as a sysctl tunable. I am aware that because it is a kernel core
>> parameter, there is already an entry under:
>>
>>    /sys/module/kernel/parameters/crash_kexec_post_notifiers
>>
>> and that allows us to read/modify it at runtime. However, I thought it should
>> also be available via sysctl, since users that want to read/set this value at
>> runtime might look there first.
>>
>> I believe there is an ongoing effort to clean up kernel/sysctl.c, but it wasn't
>> clear to me if this entry (and perhaps the other panic related entries too)
>> should be placed on kernel/panic.c. I wanted to verify first that this change
>> would be welcomed before doing additional refactoring work.
>>
>> I'd appreciate any comments or suggestions.
>>
>> Thank you,
>> Alejandro
> Hi Alejandro, thanks for you patch. I have a "selfish" concern though,
> I'll expose it here.
>
> I'm working a panic refactor, in order to split the panic notifiers in
> more lists - good summary of this discussion at [0].
> I'm in the half of the patches, hopefully next 2 weeks I have something
> ready to submit (I'll be out next week).
>
> As part of this effort, I plan to have a more fine-grained control of
> this parameter, and it's going to be a sysctl, but not
> "crash_kexec_post_notifiers" - this one should be kept I guess due to
> retro-compatibility, but it'd be a layer on top oh the new one.
It would be great to provide finer control and isolate the riskier 
modifiers.

I am using crash_kexec_post_notifiers to control behavior of pvpanic and 
pstore and there is not an urgent need for my change, so I don't mind 
waiting for the new interface to evolve. Please copy me if possible on 
future submissions.

Thank you,
Alejandro

> With that said, unless you have urgent needs for this patch to be
> reviewed/merged , I'd like to ask you to wait the series and I can loop
> you there, so you may review/comment and see if it fits your use case.
>
> Thanks,
>
>
> Guilherme
>
>
> [0] https://lore.kernel.org/lkml/YfPxvzSzDLjO5ldp@alley/