linux-kernel - Re: [PATCH 3/3] panic: Allow printing extra panic information on kdump

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Message-ID: <Yckaz79zg5HdEgcH@dhcp-128-65.nay.redhat.com>
Date:   Mon, 27 Dec 2021 09:45:51 +0800
From:   Dave Young <dyoung@...hat.com>
To:     "Guilherme G. Piccoli" <gpiccoli@...lia.com>
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-doc@...r.kernel.org, mcgrof@...nel.org,
        keescook@...omium.org, yzaikin@...gle.com,
        akpm@...ux-foundation.org, feng.tang@...el.com,
        siglesias@...lia.com, kernel@...ccoli.net,
        kexec@...ts.infradead.org
Subject: Re: [PATCH 3/3] panic: Allow printing extra panic information on
 kdump

On 12/25/21 at 04:21pm, Guilherme G. Piccoli wrote:
> On 23/12/2021 22:35, Dave Young wrote:
> > Hi Guilherme,
> > [...]
> > If only the doc update, I think it is fine to be another follup-up
> > patch.
> > 
> > About your 1st option in patch log, there is crash_kexec_post_notifiers
> > kernel param which can be used to switch on panic notifiers before kdump
> > bootup.   Another way probably you can try to move panic print to be
> > panic notifier. Have this been discussed before? 
> > 
> 
> Hey Dave, thanks for the suggestion. I've considered that but didn't
> like the idea. My reasoning was: allowing post notifiers on kdump will
> highly compromise the reliability, whereas the panic_print is a solo
> option, and not very invasive.
> 
> To mix it with all panic notifiers would just increase a lot the risk of
> a kdump failure. Put in other words: if I'm a kdump user and in order to
> have this panic_print setting I'd also need to enable post notifiers,
> certainly I'll not use the feature, 'cause I don't wanna risk kdump too
> much.

Hi Guilherme, yes, I have the same concern.  But there could be more
things like the panic_print in the future, it looks odd to have more
kernel cmdline params though.

> 
> One other option I've considered however, and I'd appreciate your
> opinion here, would be a new option on crash_kexec_post_notifiers that
> allows the users to select *which few notifiers* they want to enable.
> Currently it's all or nothing, and this approach is too heavy/risky I
> believe. Allowing customization on which post notifiers the user wants
> would be much better and in this case, having a post notifier for
> panic_print makes a lot of sense. What do you think?

It is definitely a good idea, I'm more than glad to see this if you
would like to work on this! 

> 
> Thanks!
> 

Thanks
Dave