linux-kernel - Re: [PATCH] xen/x86: set panic notifier priority to minimum

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Message-ID: <20140513183600.GA10992@potion.brq.redhat.com>
Date:	Tue, 13 May 2014 20:36:01 +0200
From:	Radim Krčmář <rkrcmar@...hat.com>
To:	David Vrabel <david.vrabel@...rix.com>
Cc:	linux-kernel@...r.kernel.org, Andrew Jones <drjones@...hat.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	xen-devel@...ts.xenproject.org
Subject: Re: [PATCH] xen/x86: set panic notifier priority to minimum

2014-05-13 18:18+0100, David Vrabel:
> On 13/05/14 17:56, Radim Krčmář wrote:
> > Execution is not going to continue after telling Xen about the crash.
> > Let other panic notifiers run by postponing the final hypercall as much
> > as possible.
> 
> I can't tell how important this fix is.

Sorry, I could have put reasoning in the commit:

Not very important, depends on long linux+xen is going to last.
This patch is thinking about users/developers that would eventually find
a problem with it, and questioned our inteligence -- it makes no sense
to use the default priority for a notifier that is (can be) final.
INT_MIN is set because I don't think that Xen indended to resume domains
after crash.  (We should reason any other value as well.)

> What notifiers does this allow to be run?  How important are they?

Priority 0 (default) or lower.  Registration is stable and paravirt does
it early, so there won't be many priority 0 users before it. (None now.)

Hardware that can be passed through (most notably graphic cards), and
few debug markers (dump_kernel_offset, hung_task_panic) are affected at
the moment.
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