linux-kernel - Re: [PATCH V2] Documentation: Improve crash_kexec_post

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Message-ID: <ZtUrX4n+HPYhyQ9z@MiWiFi-R3L-srv>
Date: Mon, 2 Sep 2024 11:05:03 +0800
From: Baoquan He <bhe@...hat.com>
To: "Guilherme G. Piccoli" <gpiccoli@...lia.com>
Cc: kexec@...ts.infradead.org, linux-doc@...r.kernel.org, vgoyal@...hat.com,
	dyoung@...hat.com, corbet@....net, linux-kernel@...r.kernel.org,
	linux-debuggers@...r.kernel.org, stephen.s.brennan@...cle.com,
	kernel@...ccoli.net, kernel-dev@...lia.com
Subject: Re: [PATCH V2] Documentation: Improve crash_kexec_post_notifiers
 description

On 08/30/24 at 03:21pm, Guilherme G. Piccoli wrote:
> Be more clear about the downsides, the upsides (yes, there are some!)
> and about code that unconditionally sets that.
> 
> Reviewed-by: Stephen Brennan <stephen.s.brennan@...cle.com>
> Signed-off-by: Guilherme G. Piccoli <gpiccoli@...lia.com>
> 
> ---
> 
> V2: Some wording improvements from Stephen, thanks!
> Also added his review tag.
> 
> V1 link: https://lore.kernel.org/r/20240830140401.458542-1-gpiccoli@igalia.com/
> 
> 
>  Documentation/admin-guide/kernel-parameters.txt | 16 ++++++++++------
>  1 file changed, 10 insertions(+), 6 deletions(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index efc52ddc6864..351730108c58 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -913,12 +913,16 @@
>  			the parameter has no effect.
>  
>  	crash_kexec_post_notifiers
> -			Run kdump after running panic-notifiers and dumping
> -			kmsg. This only for the users who doubt kdump always
> -			succeeds in any situation.
> -			Note that this also increases risks of kdump failure,
> -			because some panic notifiers can make the crashed
> -			kernel more unstable.
> +			Only jump to kdump kernel after running the panic
> +			notifiers and dumping kmsg. This option increases the
> +			risks of a kdump failure, since some panic notifiers
> +			can make the crashed kernel more unstable. In the
> +			configurations where kdump may not be reliable,
> +			running the panic notifiers can allow collecting more
> +			data on dmesg, like stack traces from other CPUS or
> +			extra data dumped by panic_print. Notice that some
> +			code enables this option unconditionally, like
> +			Hyper-V, PowerPC (fadump) and AMD SEV.
                        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
I know Hyper-V enable panic-notifiers by default, but don't remember how
PowerPC and AMD SEC behave in this aspect. While at it, can you add a
little more words to state them in log so that people can learn it?
Thanks.

>  
>  	crashkernel=size[KMG][@offset[KMG]]
>  			[KNL,EARLY] Using kexec, Linux can switch to a 'crash kernel'
> -- 
> 2.46.0
>