linux-kernel - Re: [PATCH 00/10] OOM Debug print selection and additional information

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Message-ID: <5db2d2bd-645b-8967-849a-0d1de5861742@i-love.sakura.ne.jp>
Date:   Wed, 28 Aug 2019 19:56:58 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Edward Chron <echron@...sta.com>, Qian Cai <cai@....pw>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <guro@...com>,
        Johannes Weiner <hannes@...xchg.org>,
        David Rientjes <rientjes@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Ivan Delalande <colona@...sta.com>
Subject: Re: [PATCH 00/10] OOM Debug print selection and additional
 information

On 2019/08/28 19:32, Michal Hocko wrote:
>> Speak of my cases, those who take care of their systems are not developers.
>> And they afraid changing code that runs in kernel mode. They unlikely give
>> permission to install SystemTap/eBPF scripts. As a result, in many cases,
>> the root cause cannot be identified.
> 
> Which is something I would call a process problem more than a kernel
> one. Really if you need to debug a problem you really have to trust
> those who can debug that for you. We are not going to take tons of code
> to the kernel just because somebody is afraid to run a diagnostic.
> 

This is a problem of kernel development process.

>> Moreover, we are talking about OOM situations, where we can't expect userspace
>> processes to work properly. We need to dump information we want, without
>> counting on userspace processes, before sending SIGKILL.
> 
> Yes, this is an inherent assumption I was making and that means that
> whatever dynamic hooks would have to be registered in advance.
> 

No. I'm saying that neither static hooks nor dynamic hooks can work as
expected if they count on userspace processes. Registering in advance is
irrelevant. Whether it can work without userspace processes is relevant.

Also, out-of-tree codes tend to become defunctional. We are trying to debug
problems caused by in-tree code. Breaking out-of-tree debugging code just
because in-tree code developers don't want to pay the burden of maintaining
code for debugging problems caused by in-tree code is a very bad idea.