linux-ext4 - REGRESSION: [PATCH 04/12] ext4: Disable merging of uninitialized extents

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20130209171015.GC8091@thunk.org>
Date:	Sat, 9 Feb 2013 12:10:15 -0500
From:	Theodore Ts'o <tytso@....edu>
To:	Jan Kara <jack@...e.cz>, Dmitry Monakhov <dmonakhov@...nvz.org>
Cc:	linux-ext4@...r.kernel.org
Subject: REGRESSION: [PATCH 04/12] ext4: Disable merging of uninitialized
 extents

On Fri, Jan 18, 2013 at 01:00:38PM +0100, Jan Kara wrote:
> Merging of uninitialized extents creates all sorts of interesting race
> possibilities when writeback / DIO races with fallocate. Thus
> ext4_convert_unwritten_extents_endio() has to deal with a case where
> extent to be converted needs to be split out first. That isn't nice
> for two reasons:
> 
> 1) It may need allocation of extent tree block so ENOSPC is possible.
> 2) It complicates end_io handling code
> 
> So we disable merging of uninitialized extents which allows us to simplify
> the code. Extents will get merged after they are converted to initialized
> ones.
> 
> Reviewed-by: Zheng Liu <wenqing.lz@...bao.com>
> Signed-off-by: Jan Kara <jack@...e.cz>

Sorry for not noticing this earlier, but this patch is causing a
regression.  It is loading to test 113 failing when dioread_nolock is
used:

113	[   47.619363] EXT4-fs error (device vdb): ext4_convert_unwritten_extents_endio:3411: i
node #10951: comm kworker/u:0: Written extent modified before IO finished: extent logical block
 1024, len 1024; IO logical block 1024, len 127
[   47.619363] 
[   47.623239] EXT4-fs warning (device vdb): ext4_convert_unwritten_extents:4522: inode #10951:
 block 1024: len 127: ext4_ext_map_blocks returned -5
[   47.628975] EXT4-fs (vdb): failed to convert unwritten extents to written extents -- potenti
al data loss!  (inode 10951, offset 4194304, size 520192, error -5)


As a result, I am considering whether or not I should to drop the
following patches from the ext4 tree:

e63dd9c ext4: disable merging of uninitialized extents
de39534 ext4: remove unnecessary wait for extent conversion in ext4_fallocate()
37bf0a8 ext4: ext4_split_extent should take care of extent zeroout

I know that these patches fix other potential races which causes data
loss, but they've been around for a while, and in practice seem to be
relatively rarely hit.

Jan, Dmitry, any chance you can take a look at this, and give me
suggestions about how to proceed at this point?

Thanks,

						- Ted
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html