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

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Date:	Wed, 23 Sep 2015 15:49:12 +0300
From:	Artem Bityutskiy <dedekind1@...il.com>
To:	Theodore Ts'o <tytso@....edu>, Tejun Heo <tj@...nel.org>
Cc:	axboe@...nel.dk, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, lizefan@...wei.com,
	cgroups@...r.kernel.org, hannes@...xchg.org, kernel-team@...com,
	adilger.kernel@...ger.ca, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 2/2] ext4: implement cgroup writeback support

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@...nel.org>
> > Cc: "Theodore Ts'o" <tytso@....edu>
> > Cc: Andreas Dilger <adilger.kernel@...ger.ca>
> > Cc: linux-ext4@...r.kernel.org
> 
> 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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