Re: ext4 data corruption in 6.1 stable tree (was Re: [PATCH 5.15 000/297] 5.15.140-rc1 review)

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Tue, Dec 05, 2023 at 09:55:08AM -0800, Guenter Roeck wrote:
> On Tue, Dec 05, 2023 at 01:21:22PM +0100, Jan Kara wrote:
> [ ... ]
> > 
> > So I've got back to this and the failure is a subtle interaction between
> > iomap code and ext4 code. In particular that fact that commit 936e114a245b6
> > ("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 ->end_io
> > handler returns non-zero value (which the new ext4 ->end_io handler does),
> > file pos doesn't get updated, after this commit it doesn't get updated only
> > if the return value is < 0.
> > 
> > The commit got merged in 6.5-rc1 so all stable kernels that have
> > 91562895f803 ("ext4: properly sync file size update after O_SYNC direct
> > IO") before 6.5 are corrupting data - I've noticed at least 6.1 is still
> > carrying the problematic commit. Greg, please take out the commit from 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!
> > 
> 
> Thanks a lot for the update.
> 
> Turns out this is causing a regression in chromeos-6.1, and reverting the
> offending patch fixes the problem. I suspect anyone running v6.1.64+ may
> have a problem.

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.

greg k-h