linux-kernel - Re: [PATCH V3] panic: Move panic

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Message-ID: <4de89aeb-c127-908c-b403-f9cea128a0b0@igalia.com>
Date:   Thu, 20 Jan 2022 12:51:11 -0300
From:   "Guilherme G. Piccoli" <gpiccoli@...lia.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Baoquan He <bhe@...hat.com>, linux-kernel@...r.kernel.org,
        akpm@...ux-foundation.org, kernel@...ccoli.net,
        senozhatsky@...omium.org, rostedt@...dmis.org,
        john.ogness@...utronix.de, feng.tang@...el.com,
        kexec@...ts.infradead.org, dyoung@...hat.com,
        keescook@...omium.org, anton@...msg.org, ccross@...roid.com,
        tony.luck@...el.com
Subject: Re: [PATCH V3] panic: Move panic_print before kmsg dumpers

On 20/01/2022 06:39, Petr Mladek wrote:
> [...]
> It makes perfect sense to disable the watchdogs during panic().
> For example, rcu_panic() just sets a variable:
> 
> static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr)
> {
> 	rcu_cpu_stall_suppress = 1;
> 	return NOTIFY_DONE;
> }
> 
> It is quick and super-safe. It might make sense to implement similar
> thing for other watchdogs and do something like:
> 
> void panic_supress_watchdogs(void)
> {
> 	rcu_panic();
> 	softlockup_watchog_panic();
> 	wq_watchog_panic();
> }
> 
> It might be caller early in panic().
> 

For reference, I saw your great input about this subject in another
related thread, which I think we should mention here:

https://lore.kernel.org/lkml/Yel8WQiBn%2FHNQN83@alley/


> JFYI, there is an extension for the crash tool that might be able to read
> the trace log, see https://crash-utility.github.io/extensions.html
> 
> I haven't tested it myself yet.

Thanks, nice to know =)