linux-kernel - Re: [PATCH V2] panic: Move panic

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Date:   Thu, 13 Jan 2022 12:50:06 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     "Guilherme G. Piccoli" <gpiccoli@...lia.com>
Cc:     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 V2] panic: Move panic_print before kmsg dumpers

On Thu 2022-01-06 18:28:35, Guilherme G. Piccoli wrote:
> The panic_print setting allows users to collect more information in a
> panic event, like memory stats, tasks, CPUs backtraces, etc.
> This is a pretty interesting debug mechanism, but currently the print
> event happens *after* kmsg_dump(), meaning that pstore, for example,
> cannot collect a dmesg with the panic_print information.

> --- a/kernel/panic.c
> +++ b/kernel/panic.c
> @@ -249,7 +252,7 @@ void panic(const char *fmt, ...)
>  	 * show some extra information on kernel log if it was set...
>  	 */
>  	if (kexec_crash_loaded())
> -		panic_print_sys_info();
> +		panic_print_sys_info(false);

panic_print_sys_info(false) will be called twice when both
kexec_crash_loaded() and _crash_kexec_post_notifiers are true.

Do we really need to call panic_print_sys_info() here? All information
provided by panic_print_sys_info(false) can be found also in
the crash dump.

>  	/*
>  	 * If we have crashed and we have a crash kernel loaded let it handle
> @@ -283,6 +286,8 @@ void panic(const char *fmt, ...)
>  	 */
>  	atomic_notifier_call_chain(&panic_notifier_list, 0, buf);
>  
> +	panic_print_sys_info(false);

This is where the info might be printed 2nd time.

> +
>  	kmsg_dump(KMSG_DUMP_PANIC);
>  
>  	/*

Otherwise, the change makes sense to me.

Best Regards,
Petr