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SubjectRe: KVM induced panic on 2.6.38[2367] & 2.6.39

On Wed, Jun 01, 2011 at 08:37:25AM +0800, Brad Campbell wrote:
> On 01/06/11 06:31, Hugh Dickins wrote:
> > Brad, my suspicion is that in each case the top 16 bits of RDX have been
> > mysteriously corrupted from ffff to 0000, causing the general protection
> > faults. I don't understand what that has to do with KSM.
> >
> > But it's only a suspicion, because I can't make sense of the "Code:"
> > lines in your traces, they have more than the expected 64 bytes, and
> > only one of them has a ">" (with no"<") to mark faulting instruction.
> >
> > I did try compiling the 2.6.39 kernel from your config, but of course
> > we have different compilers, so although I got close, it wasn't exact.
> >
> > Would you mind mailing me privately (it's about 73MB) the "objdump -trd"
> > output for your original vmlinux (with KSM on)? (Those -trd options are
> > the ones I'm used to typing, I bet not they're not all relevant.)
> >
> > Of course, it's only a tiny fraction of that output that I need,
> > might be better to cut it down to remove_rmap_item_from_tree and
> > dup_fd and ksm_scan_thread, if you have the time to do so.
> Would you believe about 20 seconds after I pressed send the kernel oopsed.
> oops reproduced here, but an un-munged version is in that directory
> alongside the kernel.
> [36542.880228] general protection fault: 0000 [#1] SMP

Reminds me of another oops that was reported on the kvm list for with message id 4D8C6110.6090204. There the top 16 bits of
rsi were flipped and it was a general protection too because of
hitting on the not mappable virtual range.

That oops happened in kvm_unmap_rmapp though, but it looked memory
corruption (Avi suggested use after free) but it was a production
system so we couldn't debug it further.

I recommend next thing to reproduce again with 2.6.39 or
3.0.0-rc1. Let's fix your scsi trouble if needed but it's better you
test with 2.6.39.

We'd need chmod +r vmlinux on private/003_kernel_oops/


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