linux-kernel - Re: [PATCH V4] notifier/panic: Introduce panic_notifier

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Date:   Mon, 7 Mar 2022 11:25:30 -0300
From:   "Guilherme G. Piccoli" <gpiccoli@...lia.com>
To:     "bhe@...hat.com" <bhe@...hat.com>
Cc:     Petr Mladek <pmladek@...e.com>,
        "d.hatayama@...itsu.com" <d.hatayama@...itsu.com>,
        "kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dyoung@...hat.com" <dyoung@...hat.com>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "vgoyal@...hat.com" <vgoyal@...hat.com>,
        "stern@...land.harvard.edu" <stern@...land.harvard.edu>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "andriy.shevchenko@...ux.intel.com" 
        <andriy.shevchenko@...ux.intel.com>,
        "corbet@....net" <corbet@....net>,
        "halves@...onical.com" <halves@...onical.com>,
        "kernel@...ccoli.net" <kernel@...ccoli.net>
Subject: Re: [PATCH V4] notifier/panic: Introduce panic_notifier_filter

On 07/03/2022 11:04, bhe@...hat.com wrote:
> [...]
> Ah, sorry, I even didn't notice that. That's awesome if we can make use
> of that. While I still have concerns:
> 

Thanks, nice that you liked the idea.

> 1) about those we have decided to take out from panic notifier list and
> put before kdump, e.g the Hypver-V notifier, how will we do with it? Are
> we going to handle them as we have discussed?
> 

While implementing that I will think of something, but if
understood/remember correctly Hyper-V gonna be one of the first to run
in the first notifier list proposed by Petr - so we might still use
ordering by priority there, having Hyper-V being the first heh

> 2) Combing and settling priority for all existing panic notifier looks
> great, even though it will take some effort. How about the later newly
> added one? How can we guarantee that those new notifiers are getting
> appropriate priority to mark their order? Sometime we even don't know
> a new panic notifier is added since code change may be made in any
> component or driver.
> 

This is a great point! How to do it? One idea is to have a special
registering function for panic notifiers that checks for priority field
missing, and good documentation is a good idea as well, always.

But if you / others have other suggestions, let me know - appreciate that.
Cheers,


Guilherme