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Re: [Xen-devel] crashes with 2.0 -- "Unable to reduce memory reservation

To: Chris Andrews <chris@xxxxxxxxxx>
Subject: Re: [Xen-devel] crashes with 2.0 -- "Unable to reduce memory reservation"
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Sat, 04 Sep 2004 16:56:27 +0100
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> When I ran 'xm destroy 3', I got the output below on the serial 
> console, and then a watchdog reboot but screen seems to have truncated 
> the lines. The second crash has untruncated output. I've added the 
> xensymoops output below.
> Any thoughts?

Yes, I think we've seen this crash ourselves. The page reference
counts are getting corrupted, so the page has been freed already, and
when free_page_type() looks for the domain pointer in the struct
pfn_info, it has already been overwritten with a CPU mask (that field
changes purpose when a page is freed).

So, type count and usage count are out of sync....

The most likely culprit is the writable page tables, but as you've
noticed the bug is hard to trigger so it's difficult to try various
configurations and be sure which are safe!

 -- Keir

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