linux-kernel - Re: [Xen-devel] [PATCH] x86/xen: Return from panic notifier

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Date:   Wed, 2 Oct 2019 09:40:11 +0200
From:   Jan Beulich <jbeulich@...e.com>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:     xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        james@...gwall.me.uk, Juergen Gross <jgross@...e.com>
Subject: Re: [Xen-devel] [PATCH] x86/xen: Return from panic notifier

On 01.10.2019 17:16, Boris Ostrovsky wrote:
> Currently execution of panic() continues until Xen's panic notifier
> (xen_panic_event()) is called at which point we make a hypercall that
> never returns.
> 
> This means that any notifier that is supposed to be called later as
> well as significant part of panic() code (such as pstore writes from
> kmsg_dump()) is never executed.

Back at the time when this was introduced into the XenoLinux tree,
I think this behavior was intentional for at least DomU-s. I wonder
whether you wouldn't want your change to further distinguish Dom0
and DomU behavior.

> There is no reason for xen_panic_event() to be this last point in
> execution since panic()'s emergency_restart() will call into
> xen_emergency_restart() from where we can perform our hypercall.

Did you consider, as an alternative, to lower the notifier's
priority?

Jan