linux-kernel - Re: [RFC] How to test panic handlers, without crashing the kernel

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Message-ID: <adeac189-87f8-4b70-9c04-3eaaf2ed7bc5@redhat.com>
Date: Thu, 7 Mar 2024 18:22:55 +0100
From: Jocelyn Falempe <jfalempe@...hat.com>
To: "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
 Michael Kelley <mhklinux@...look.com>,
 John Ogness <john.ogness@...utronix.de>,
 Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
 Daniel Vetter <daniel@...ll.ch>, Andrew Morton <akpm@...ux-foundation.org>,
 "Peter Zijlstra (Intel)" <peterz@...radead.org>,
 Josh Poimboeuf <jpoimboe@...nel.org>, Arnd Bergmann <arnd@...db.de>,
 Kefeng Wang <wangkefeng.wang@...wei.com>, Lukas Wunner <lukas@...ner.de>,
 Uros Bizjak <ubizjak@...il.com>, Petr Mladek <pmladek@...e.com>,
 Daniel Thompson <daniel.thompson@...aro.org>,
 Douglas Anderson <dianders@...omium.org>
Cc: "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
 David Airlie <airlied@...hat.com>, Thomas Zimmermann <tzimmermann@...e.de>
Subject: Re: [RFC] How to test panic handlers, without crashing the kernel

On 05/03/2024 18:50, Guilherme G. Piccoli wrote:
> On 05/03/2024 13:52, Jocelyn Falempe wrote:
>> [...]
>> Or maybe have two lists of panic notifiers, the safe and the destructive
>> list. So in case of fake panic, we can only call the safe notifiers.
>>
> 
> I tried something like that:
> https://lore.kernel.org/lkml/20220427224924.592546-1-gpiccoli@igalia.com/
> 
> There were many suggestions, a completely refactor of the idea (panic
> lists are not really seen as reliable things).

Thanks for sharing this, so it's much more complex than what I though.
> 
> Given that, I'm not really sure splitting in lists gonna fly; maybe
> restricting the test infrastructure to drm_panic plus some paths of
> panic would be enough for this debugfs interface, in principle? I mean,
> to unblock your work on the drm panic stuff.

For drm_panic, I changed the way the debugfs is calling the drm_panic 
functions in the last version:
https://patchwork.freedesktop.org/patch/581845/?series=122244&rev=9

It doesn't use the panic notifier list, but create a file for each plane 
of each device directly.
It allows to test the panic handler, not in a real panic condition, but 
that's still better than nothing.

> 
> Cheers,
> 
> 
> Guilherme
> 

Best regards,

-- 

Jocelyn