linux-kernel - Re: [PATCH v2 10/13] EDAC/altera: Skip the panic notifier if kdump is loaded

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Date:   Wed, 17 Aug 2022 21:34:41 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     "Guilherme G. Piccoli" <gpiccoli@...lia.com>
Cc:     akpm@...ux-foundation.org, bhe@...hat.com, pmladek@...e.com,
        kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-hyperv@...r.kernel.org, netdev@...r.kernel.org,
        x86@...nel.org, kernel-dev@...lia.com, kernel@...ccoli.net,
        halves@...onical.com, fabiomirmar@...il.com,
        alejandro.j.jimenez@...cle.com, andriy.shevchenko@...ux.intel.com,
        arnd@...db.de, corbet@....net, d.hatayama@...fujitsu.com,
        dave.hansen@...ux.intel.com, dyoung@...hat.com,
        feng.tang@...el.com, gregkh@...uxfoundation.org,
        mikelley@...rosoft.com, hidehiro.kawai.ez@...achi.com,
        jgross@...e.com, john.ogness@...utronix.de, keescook@...omium.org,
        luto@...nel.org, mhiramat@...nel.org, mingo@...hat.com,
        paulmck@...nel.org, peterz@...radead.org, rostedt@...dmis.org,
        senozhatsky@...omium.org, stern@...land.harvard.edu,
        tglx@...utronix.de, vgoyal@...hat.com, vkuznets@...hat.com,
        will@...nel.org, linux-edac@...r.kernel.org,
        Dinh Nguyen <dinguyen@...nel.org>,
        Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH v2 10/13] EDAC/altera: Skip the panic notifier if kdump
 is loaded

On Wed, Aug 17, 2022 at 03:45:30PM -0300, Guilherme G. Piccoli wrote:
> But happens that in the refactor we are proposing [0], some notifiers
> should run before the kdump. We are basically putting some ordering in
> the way notifiers are executed, while documenting this properly and with
> the goal of not increasing the failure risk for kdump.

What is "the failure risk for kdump"?

Some of the notifiers which run before kdump might fail and thus prevent
the machine from kdumping?

> This patch is useful so we can bring the altera EDAC notifier to run
> earlier while not increasing the risk on kdump - this operation is a bit
> "delicate" to happen in the panic scenario. The origin of this patch was
> a discussion with Tony/Peter [1], guess we can call it a "compromise
> solution".

My question stands: if kdump is loaded and the s10_edac_dberr_handler()
does not read the the fatal errors and they don't get shown in dmesg
before the machine panics, how do you intend to show that information to
the user?

Because fatal errors are something you absolutely wanna show, at least,
in dmesg!

I don't think you can "read" the errors from vmcore - they need to be
read from the hw registers before the machine dies.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette