From: Artem Bityutskiy <dedekind1@gmail.com>
Subject: Re: [PATCH 2/2] ext4: implement cgroup writeback support
Date: Thu, 24 Sep 2015 11:13:38 +0300
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Cc: Chris Mason <clm@fb.com>, linux-ext4@vger.kernel.org,
	Johannes Weiner <hannes@cmpxchg.org>, axboe@kernel.dk,
	Tejun Heo <tj@kernel.org>, linux-fsdevel@vger.kernel.org,
	lizefan@huawei.com, cgroups@vger.kernel.org,
	adilger.kernel@dilger.ca, kernel-team@fb.com,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
To: Theodore Ts'o <tytso@mit.edu>
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On Wed, 2015-09-23 at 16:48 -0400, Theodore Ts'o wrote:
> On Wed, Sep 23, 2015 at 10:47:16PM +0300, Artem Bityutskiy wrote:
> > And, by the way, I forgot this detail - I cut AC power off at the
> > end, then put it back on after a 20 seconds delay. I mean, this is
> > a
> > clean reboot, but with power cut at the end.
> 
> Is this reproducible without the power cut?  And what model SSD are
> you using, and are you sure that it has Power Loss Protection (many
> SSD vendors use power loss protection as the price discrimination
> feature between consumer-grade SSD and enterprise-grade SSD's that
> cost $$$).  If this problem wasn't showing up with 4.2, and is only
> failing with 4.3-rcX, then it might not be a hardware issue --- but
> it's also possible that there was a timing issue which was hiding a
> hardware problem.  So for the purposes of debugging, removing the
> power cut from the set of variables is a useful thing to do.

Ted, you are right that the problem may be anywhere, but since Tejun's
patch fixes it, I decided to not spend time on testing without AC power
cuts.

But I checked and on of my boxes uses an HDD, and it shows the same
problem, which makes the theory of imperfect SSD firmware being
involved less likely.

Thanks,
Artem.