Re: unexpected truncated files

[Filipe Manana <fdmanana@gmail.com>]

On Sat, Apr 4, 2020 at 8:52 PM Johannes Hirte
<johannes.hirte@datenkhaos.de> wrote:
>
> While testing with the current 5.7 development kernel, I've encountered
> some strange behaviour. I'm using Gentoo linux, and during updating the
> system I got some unexpected errors. It looked like some files were
> missing. Some investigations showed me, that files from shortly
> installed packages were truncated to zero. So for example the config
> files for apache webserver were affected. I've reinstalled apache,
> verified that the config was ok and continued the system update with the
> next package. After this, the apache config files were truncated again.
> I've found several files from different packages that were affed too,
> but only text files (configs, cmake-files, headers). Files which were
> writen, are truncated by some other write operation to the filesystem.
>
> I'm not sure, if this is really caused by btrfs, but it's the most
> obvious candidate. After switching back to 5.6-kernel, the truncation
> stopped und I was able to (re-)install the packages without any trouble.
>
> Has anyone ideas what could cause this behaviour?

It's likely due to file cloning.

I found this out yesterday but hadn't sent a patch yet, was waiting
for monday morning.
I've just sent the patch to the list:
https://patchwork.kernel.org/patch/11474453/

Since you are only getting this with small files, it's likely the
cloning of inline extents causing it, due to some changes in 5.7 that
changed the file size update logic.

Can you try it?

Thanks.

>
> --
> Regards,
>   Johannes Hirte
>


-- 
Filipe David Manana,

“Whether you think you can, or you think you can't — you're right.”