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Date: Mon, 11 Dec 2023 09:28:40 +0100
From: Pavel Machek <pavel@denx.de>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Guenter Roeck <linux@roeck-us.net>, Jan Kara <jack@suse.cz>,
	Daniel =?iso-8859-1?Q?D=EDaz?= <daniel.diaz@linaro.org>,
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	chrubis@suse.cz, linux-ext4@vger.kernel.org,
	Ted Tso <tytso@mit.edu>
Subject: Re: ext4 data corruption in 6.1 stable tree (was Re: [PATCH 5.15
 000/297] 5.15.140-rc1 review)
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Hi!

> > > So I've got back to this and the failure is a subtle interaction betw=
een
> > > iomap code and ext4 code. In particular that fact that commit 936e114=
a245b6
> > > ("iomap: update ki_pos a little later in iomap_dio_complete") is not =
in
> > > stable causes that file position is not updated after direct IO write=
 and
> > > thus we direct IO writes are ending in wrong locations effectively
> > > corrupting data. The subtle detail is that before this commit if ->en=
d_io
> > > handler returns non-zero value (which the new ext4 ->end_io handler d=
oes),
> > > file pos doesn't get updated, after this commit it doesn't get update=
d only
> > > if the return value is < 0.
> > >=20
> > > The commit got merged in 6.5-rc1 so all stable kernels that have
> > > 91562895f803 ("ext4: properly sync file size update after O_SYNC dire=
ct
> > > IO") before 6.5 are corrupting data - I've noticed at least 6.1 is st=
ill
> > > carrying the problematic commit. Greg, please take out the commit fro=
m all
> > > stable kernels before 6.5 as soon as possible, we'll figure out proper
> > > backport once user data are not being corrupted anymore. Thanks!
> > >=20
> >=20
> > Thanks a lot for the update.
> >=20
> > Turns out this is causing a regression in chromeos-6.1, and reverting t=
he
> > offending patch fixes the problem. I suspect anyone running v6.1.64+ may
> > have a problem.
>=20
> Jan, thanks for the report, and Guenter, thanks for letting me know as
> well.  I'll go queue up the fix now and push out new -rc releases.

Would someone have a brief summary here? I see 6.1.66 is out but I
don't see any "Fixes: 91562895f803" tags.

Plus, what is the severity of this? It is "data being corrupted when
using O_SYNC|O_DIRECT" or does metadata somehow get corrupted, too?

Thanks and best regards,
								Pavel
--=20
DENX Software Engineering GmbH,        Managing Director: Erika Unter
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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