linux-kernel - Re: DomU crashes during xenfb initialization

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Date:	Fri, 21 Aug 2009 15:13:52 +0200
From:	Michal Schmidt <mschmidt@...hat.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Mark McLoughlin <markmc@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: DomU crashes during xenfb initialization

Dne Fri, 21 Aug 2009 15:09:22 +0200 Michal Schmidt napsal:
> Dne Fri, 21 Aug 2009 12:40:59 +0200 Michal Schmidt napsal:
> > So it crashes during Xen framebuffer initialization. And indeed,
> > disabling CONFIG_XEN_FBDEV_FRONTEND helps, the kernel then boots
> > fine.
> > 
> > I git-bisected it and found that the bug was introduced by this
> > commit: commit ced40d0f3e8833bb8d7d8e2cbfac7da0bf7008c4
> > Author: Jeremy Fitzhardinge <jeremy@...p.org>
> > Date:   Fri Feb 6 14:09:44 2009 -0800
> > 
> >     xen: pack all irq-related info together
> 
> It's not this commit's fault. It just uncovered a latent bug.
> info->irq is -1 in xenfb_send_event(), so it calls
> notify_remote_via_irq(-1) which then dereferences out-of-array memory.

In xenfb_probe(), xenfb_connect_backend() is called after
register_framebuffer(). That looks suspicious. I'll see if switching
the order helps.

Michal
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