unexpected truncated files

unexpected truncated files

[Johannes Hirte]

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?

-- 
Regards,
  Johannes Hirte

Re: unexpected truncated files

[Filipe Manana]

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.”

Re: unexpected truncated files

[Johannes Hirte]

On 2020 Apr 04, Filipe Manana wrote:
> 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.

Yes, this was it. Installing the second package for triggering the
truncation was a coincidence. Installing the first package (appache
here) and rebooting triggered the error reliable. With portage (the package
manager from Gentoo) everything is compiled and installed to a a
location on /tmp. After this, the content is copied to the target
location and seems to be done with cloning. With your patch the problem
doesn't occur anymore.

-- 
Regards,
  Johannes Hirte

Re: unexpected truncated files

[Filipe Manana]

On Sun, Apr 5, 2020 at 3:51 PM Johannes Hirte
<johannes.hirte@datenkhaos.de> wrote:
>
> On 2020 Apr 04, Filipe Manana wrote:
> > 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.
>
> Yes, this was it. Installing the second package for triggering the
> truncation was a coincidence. Installing the first package (appache
> here) and rebooting triggered the error reliable. With portage (the package
> manager from Gentoo) everything is compiled and installed to a a
> location on /tmp. After this, the content is copied to the target
> location and seems to be done with cloning. With your patch the problem
> doesn't occur anymore.

Thanks for testing it.
I'll add reported-by and test-by tags to the patch.

>
> --
> Regards,
>   Johannes Hirte
>


-- 
Filipe David Manana,

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