Re: [PATCH 2/2] ext4: implement cgroup writeback support

[Artem Bityutskiy]

On Tue, 2015-07-21 at 23:56 -0400, Theodore Ts'o wrote:
> > v2: Updated for MS_CGROUPWB -> SB_I_CGROUPWB.
> > 
> > Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
> > Cc: "Theodore Ts'o" <tytso@xxxxxxx>
> > Cc: Andreas Dilger <adilger.kernel@xxxxxxxxx>
> > Cc: linux-ext4@xxxxxxxxxxxxxxx
> 
> Thanks, applied.

Hi, this patch introduces a regression - a major one, I'd say.

Symptoms: copy a bunch of file, run sync, then run 'reboot', and after
you boot up the copied files are corrupted. So basically the user
-visible symptom is that 'sync' does not work.

I quite an effort to bisect it, but it led me to this patch.

If I take the latest upstream (v4.3-rc2+), and revert this patch:

001e4a8 ext4: imlpement cgroup writeback support

then the problem goes away - files are not corrupted after reboot.

I use ext4 on top of a "bare" partition, no LVM or dm layers involved.

I use Fedora 22 with all the latest package updates, and I only change
the kernel there.

The corruption seems to be that the start with a bunch of zeroes
instead of the real data, but I did not check carefully, looked only at
one file briefly.

Artem.

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