[Pkg-xen-devel] ioatdma: Boot process hangs then reboots when using Xen + Linux 3.2

[Dan Williams]

[replying from phone]

WARN_ON may work, but then kernel may be subject random hangs from missed
i/o completions.  Is xen32 using vt-d?  Just wondering if writes from ioat
device are getting misdirected.

--
Dan
On Mar 1, 2012 9:57 PM, "Jonathan Nieder" <jrnieder at gmail.com> wrote:

> Hi Dan,
>
> Thomas and William (cc-ed) have been having trouble loading the
> ioatdma driver on a 32-bit Xen dom0.  The module loads automatically
> at boot time and trips
>
>        BUG_ON(active && !seen_current); /* no active descs have written a
> completion? */
>
> from drivers/dma/ioat/dma_v2.c.  That check has been present since
> 5cbafa65b92e (ioat2,3: convert to a true ring buffer, 2009-08-26).
> The bug is probably in Xen code and seems to be a regression (the bug
> is present in 3.2 but not 3.1.8).
>
> Thomas Goirand wrote:
> > On 03/01/2012 11:53 PM, Bastian Blank wrote:
> >> On Thu, Mar 01, 2012 at 06:02:15PM +0800, Thomas Goirand wrote:
>
> >>>                     Any clue why I don't see crashes without Xen, with
> a
> >>> 64 bits kernel, or with earlier versions of Linux (eg: 3.1 for
> example)?
> >>
> >> xen/i386 uses a different memory model to anything else, this may be a
> >> problem.
> [...]
> > Replacing BUG_ON by a WARN_ON, and adding #define DEBUG 1 on top of
> > dma_v2.c, my kernel booted, and I had the attached dmesg output.
> >
> > Blacklisting the ioatdma kernel module of course, solved the issue.
> >
> > I hope that helps, please let me know if I should do more to help. If
> > you need access to my server, that's possible (I use it only for
> > packaging XCP and some tests...).
>
> I don't expect you to debug this Xen-specific bug, but I'm wondering:
> is there any reason this check has to be a BUG_ON instead of a
> WARN_ON?  If there is some way to recover when the impossible happens,
> that would make using and debugging the kernel a little easier.
>
> Curious,
> Jonathan
>
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