linux-kernel - Re: [PATCH] x86/mce/dev-mcelog: Call mce_register_decode

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Message-ID: <YR/Oxark0bhLlona@zn.tnic>
Date:   Fri, 20 Aug 2021 17:48:21 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     "Luck, Tony" <tony.luck@...el.com>
Cc:     x86@...nel.org, linux-edac@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Sumanth Kamatala <skamatala@...iper.net>
Subject: Re: [PATCH] x86/mce/dev-mcelog: Call mce_register_decode_chain()
 much earlier

On Fri, Aug 20, 2021 at 07:43:14AM -0700, Luck, Tony wrote:
> How can the kernel tell that all consumers have registered? Is there
> some new kernel crystal ball functionality that can predict that an
> EDAC driver module is going to be loaded at some point in the future
> when user space is up and running :-)

The crystal ball is called mcheck_late_init(). There's even:

        /*
         * Flush out everything that has been logged during early boot, now that
         * everything has been initialized (workqueues, decoders, ...).
         */
        mce_schedule_work();

in there. That thing is late_initcall() and by that time mcelog should
have been registered. And I wonder why isn't that working as expected...

> I think the best we could do would be to set a timer for some point
> far enough out (one minute?, two minutes?) to give a chance for
> modules to load.

Forget modules - only the built-in stuff. We cannot be waiting
indefinitely until someone loads mcelog for decoding.

-- 
Regards/Gruss,
    Boris.

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