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Re: [Xen-devel] PATCH for NULL pointer in netback_uevent

To: "James Harper" <james.harper@xxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] PATCH for NULL pointer in netback_uevent
From: "Jan Beulich" <JBeulich@xxxxxxxxxx>
Date: Fri, 28 May 2010 08:15:05 +0100
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>>> On 28.05.10 at 02:58, "James Harper" <james.harper@xxxxxxxxxxxxxxxx> wrote:
> The following is sufficient to get domain creation working on my server
> (see threads "null-pointer access in netback_uevent" and "oops starting
> domain on 4.0.0  +"). I'm not sure if it's the right
> solution though - should we expect a call to netback_uevent before the
> vif is properly set up? All I'm doing is returning 0 (success?) if the
> drvdata hasn't been set yet.

We've seen this just now too (with our non-pv-ops kernel). Since this
can be called due to sysfs reads (starting in 2.6.22), the function
must be prepared to be called at any time. I do think, however, that
it should provide as much data as possible in this state, i.e. not
plainly return zero in that case, but at least add the "script=" setting
(which is independent of "be" being NULL).

Even then we still depend on uevent not caching the output (but
rather re-issuing the read) once the backend for the new vif is fully
set up.


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