Re: [Qemu-devel] Help debugging a regression in KVM Module

[Peter Lieven <pl@kamp.de>]

Am 14.08.2015 um 22:01 schrieb Alex Bennée:
> Peter Lieven <pl@kamp.de> writes:
>
>> Hi,
>>
>> some time a go I stumbled across a regression in the KVM Module that has been introduced somewhere
>> between 3.17 and 3.19.
>>
>> I have a rather old openSUSE guest with an XFS filesystem which realiably crashes after some live migrations.
>> I originally believed that the issue might be related to my setup with a 3.12 host kernel and kvm-kmod 3.19,
>> but I now found that it is also still present with a 3.19 host kernel with included 3.19 kvm module.
>>
>> My idea was to continue testing on a 3.12 host kernel and then bisect all commits to the kvm related parts.
>>
>> Now my question is how to best bisect only kvm related changes (those
>> that go into kvm-kmod)?
> In general I don't bother. As it is a bisection you eliminate half the
> commits at a time you get their fairly quickly anyway. However you can
> tell bisect which parts of the tree you car about:
>
>    git bisect start -- arch/arm64/kvm include/linux/kvm* include/uapi/linux/kvm* virt/kvm/

After some experiments I was able to find out the bad commit that introduced the regression:

commit f30ebc312ca9def25650b4e1d01cdb425c310dca
Author: Radim Krčmář <rkrcmar@redhat.com>
Date:   Thu Oct 30 15:06:47 2014 +0100

It seems that this optimisation is not working reliabliy after live migration. I can't reproduce if
I take a 3.19 kernel and revert this single commit.

Peter