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From: "Guilherme G. Piccoli" <gpiccoli-wEGTBA9jqPzQT0dZR+AlfA@public.gmane.org>
Subject: Re: [PATCH 19/30] panic: Add the panic hypervisor notifier list
Date: Wed, 18 May 2022 10:16:20 -0300
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To: Petr Mladek <pmladek-IBi9RG/b67k@public.gmane.org>
Cc: David Gow <davidgow-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, Evan Green <evgreen-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>, Julius Werner <jwerner-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>, Scott Branden <scott.branden-dY08KVG/lbpWk0Htik3J/w@public.gmane.org>, bcm-kernel-feedback-list-dY08KVG/lbpWk0Htik3J/w@public.gmane.org, Sebastian Reichel <sre-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, linux-pm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Florian Fainelli <f.fainelli-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org, bhe-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, kexec-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linuxppc-dev-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org, linux-alpha-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, linux-edac-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-hyperv-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-leds-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mips-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-parisc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-remoteproc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-s390-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-um-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, linux-xtensa-PjhNF2WwrV/0Sa2dR60CXw@public.gmane.org

On 18/05/2022 04:58, Petr Mladek wrote:
> [...]
>> I does similar things like kmsg_dump() so it should be called in
>> the same location (after info notifier list and before kdump).
>>
>> A solution might be to put it at these notifiers at the very
>> end of the "info" list or make extra "dump" notifier list.
> 
> I just want to point out that the above idea has problems.
> Notifiers storing kernel log need to be treated as kmsg_dump().
> In particular, we would  need to know if there are any.
> We do not need to call "info" notifier list before kdump
> when there is no kernel log dumper registered.
> 

Notifiers respect the priority concept, which is just a number that
orders the list addition (and the list is called in order).

I've used the last position to panic_print() [in patch 25] - one idea
here is to "reserve" the last position (represented by INT_MIN) for
notifiers that act like kmsg_dump(). I couldn't find any IIRC, but that
doesn't prevent us to save this position and comment about that.

Makes sense to you ?
Cheers!