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RE: [Xen-devel] segfault in VM

To: Derek Glidden <dglidden@xxxxxxxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] segfault in VM
From: James Harper <JamesH@xxxxxxxxxxxxxxxx>
Date: Mon, 19 Jul 2004 15:50:24 +1000
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Thread-topic: [Xen-devel] segfault in VM
that sounds like the same sort of errors i'm getting which appeared to be filesystem corruption. First the corruption starts, then everything you do causes a segfault, although i've only seen funny things happen in dom0.
In the limited testing i've done it looks like dom0 by itself is stable, but crashes start occuring once I start up other domains and work dom0 hard (other domains running under light load). I'm running this script in dom0:
while [ 1 = 1 ]
 diff file3 file4 && echo okay
where file3 and file4 are around 300mb files, and the vm has 128mb of memory with no swap. This ensures that none of the file is cached so there's lots of I/O.
When i've seen it crash most readily has been when i'm running a few other domains and then start running dom0 out of memory, but nothing conclusive yet.
I'll let this test keep running for another hour (otherwise idle, no other domains running) or so then start my running-out-of-memory program.
I wonder if it is coincidence that we both have smp boxes... each of the domains only sees 1 cpu so I wouldn't have thought that would be a problem unless there's a race in xen itself.

From: Derek Glidden
Sent: Mon 19/07/2004 3:22 PM
To: xen-devel@xxxxxxxxxxxxxxxxxxxxx
Subject: [Xen-devel] segfault in VM

Maybe related or maybe not, but it was the same VM getting all the 
scheduling time in my previous post.  (SMP Celeron box with 512M of 
RAM, no himem enabled.)

At the time, four VMs were all compiling, with dom0 copying a linux 
source tree from one place to another with rsync.  Everything copacetic 
until I started the big rsync in dom0, where within a minute or so, vm2 
bombed.  No messages on the dom0 console or in the VM other than the 
"Segmentation Fault" in the VM during compliation.

However XEN (compiled with debug=y) console spits out:

(XEN) (file=x86_32/emulate.c, line=228) Bailing: not a -ve offset into 
4GB segment.

at the time of the segmentation fault.

(and there are lots of these, pretty much any time there is heavy i/o 
on the machine, all with the same values:)

(XEN) (file=traps.c, line=466) GPF (0004): fc5277a8 -> fc52a294

Any further activity inside vm2 results in more segmentation faults and 
more "Bailing" messages.  The other VMs and dom0 seem to be ok.

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