Re: Problems with c8bb23cbdbe3 on ppc64le

[Max Reitz]

On 21.10.19 15:33, Max Reitz wrote:
> On 10.10.19 17:17, Max Reitz wrote:
>> Hi everyone,
>>
>> (CCs just based on tags in the commit in question)
>>
>> I have two bug reports which claim problems of qcow2 on XFS on ppc64le
>> machines since qemu 4.1.0.  One of those is about bad performance
>> (sorry, is isn’t public :-/), the other about data corruption
>> (https://bugzilla.redhat.com/show_bug.cgi?id=1751934).
>>
>> It looks like in both cases reverting c8bb23cbdbe3 solves the problem
>> (which optimized COW of unallocated areas).
>>
>> I think I’ve looked at every angle but can‘t find what could be wrong
>> with it.  Do any of you have any idea? :-/
> 
> I now have a reproducer with CentOS, so it’s actually useful outside of
> Red Hat:

I’ve run this test with various configurations, and the installation
does not fail on tmpfs, ext4, btrfs; or without cache.direct=on,aio=native.

(So the installation only fails on xfs and aio=native.  I’ve tried both
virtio-scsi and virtio-blk, but it fails with both.  I did test a
loop-mounted xfs volume, and the installation fails there, too,
regardless of whether the raw xfs image is placed on ext4 or tmpfs.[1])

Unfortunately I still don’t have a more concise reproducer that would
clearly show that this is a kernel bug.  So for the time being I still
don’t know what causes it.

Max

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