Re: [Qemu-devel] Broken aarch64 by qcow2: skip writing zero buffers to empty COW areas [v2]

[Anton Nefedov]

On 21/8/2019 5:14 PM, Lukáš Doktor wrote:
> Hello guys,
> 
> First attempt was rejected due to zip attachment, let's try it again with 
> just Avocado-vt debug.log and serial console log files attached.
> 
> I bisected a regression on aarch64 all the way to this commit: "qcow2: skip 
> writing zero buffers to empty COW areas" 
> c8bb23cbdbe32f5c326365e0a82e1b0e68cdcd8a. Would you please have a look at it?
> 
> My reproducer is running kickstart installation of RHEL-8 from DVD on aarch64 
> gicv3 machine, which never finishes since this commit, where anaconda 
> complains about package installation, occasionally there are also XFS 
> metadata corruption messages on serial console:
> 

hi,

this looks scary :( I doubt that it can have anything to do with aarch64
but rather a really tricky timing (or, possibly, a broken environment
like broken fallocate() on a host? who knows..)

Is it always the same machine you observe this issue on? Did you try
others?

I just wonder if it's worth to try to reproduce it on my machine
(and I don't have aarch64 on hand now). I can probably come up with
some torture test that will continuously write to qcow2 with random
offsets/sizes and verify the result.

If you could kindly reproduce it again then we can probably start with
enabling qemu traces by appending
  " -trace bdrv* -trace qcow2* -trace file=/some_huge_partition/qemu.log"
to the command line.

Beware that it's going to produce a huge amount of logs.

Also, the corrupted image and the serial log will be required for
investigation.

thanks,

/Anton