From: Jan Kara <jack@suse.cz>
To: Dmitry Monakhov <dmonakhov@openvz.org>
Cc: Jan Kara <jack@suse.cz>, Ted Tso <tytso@mit.edu>,
linux-ext4@vger.kernel.org
Subject: Re: [PATCH 04/12] ext4: Disable merging of uninitialized extents
Date: Thu, 31 Jan 2013 13:39:30 +0100 [thread overview]
Message-ID: <20130131123930.GA4612@quack.suse.cz> (raw)
In-Reply-To: <87a9rpssj8.fsf@openvz.org>
On Thu 31-01-13 11:47:23, Dmitry Monakhov wrote:
> On Thu, 24 Jan 2013 13:49:45 +0400, Dmitry Monakhov <dmonakhov@openvz.org> wrote:
> > On Fri, 18 Jan 2013 13:00:38 +0100, Jan Kara <jack@suse.cz> 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
> > As we already discussed your idea is 100% correct, but even with
> > what patch I still able to trigger situation where split it required.
> > I've got following error with this patch applied on top of 7f5118629f7
> > EXT4-fs error (device dm-3): ext4_convert_unwritten_extents_endio:3411:
> > inode #12: comm kworker/u:4: Written extent modified before IO finished:
> > extent logical block 1379787, len 64; IO logical block 1379787, len 21
> >
> > ------------[ cut here ]------------
> > WARNING: at fs/ext4/extents.c:4518
> > ext4_convert_unwritten_extents+0x149/0x210 [ext4]()
> OK I've found it. I'm a bit disappointed, it is even not a race
> condition, but simple corruption.
> Patch is available here: http://article.gmane.org/gmane.comp.file-systems.ext4/36762
> link for sain mailer client: <1359617098-18451-1-git-send-email-dmonakhov@openvz.org>
> After this bug was fixed it is safe to apply both Jan's patches:
> [PATCH 04/12] ext4: Disable merging of uninitialized extents
> [PATCH 05/12] ext4: Remove unnecessary wait for extent conversion in ext4_fallocate()
> At least it survives after all my tests.
Thanks for debugging this. I was looking into the code but it didn't come
to my mind what happens when ext4_ext_split() fails.
> BTW: It is appeared that ext4_debug() infrastructure is almost unusable
> because based on printk() instead of light-wait event tracing infrastructure.
> I'm now work on patch-set which fix that.
That would be certainly welcome. ext4_debug() infrastructure comes from
times when tracing didn't exist so we used what we could. These days it's
cumbersome...
Honza
--
Jan Kara <jack@suse.cz>
SUSE Labs, CR
next prev parent reply other threads:[~2013-01-31 12:39 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-18 12:00 [PATCH 0/12 v2] ext4: Several simplifications and fixes Jan Kara
2013-01-18 12:00 ` [PATCH 01/12] ext4: Always use ext4_bio_write_page() for writeout Jan Kara
2013-01-28 14:31 ` Theodore Ts'o
2013-01-18 12:00 ` [PATCH 02/12] ext4: Use redirty_page_for_writepage() in ext4_bio_write_page() Jan Kara
2013-01-28 14:34 ` Theodore Ts'o
2013-01-18 12:00 ` [PATCH 03/12] ext4: Remove bogus wait for unwritten extents in ext4_ind_direct_IO Jan Kara
2013-01-22 11:11 ` Dmitry Monakhov
2013-01-22 13:44 ` Jan Kara
2013-01-22 14:12 ` Dmitry Monakhov
2013-01-22 15:21 ` Jan Kara
2013-01-22 14:22 ` Zheng Liu
2013-01-22 15:22 ` Jan Kara
2013-01-22 16:00 ` Zheng Liu
2013-01-22 23:14 ` Jan Kara
2013-01-23 6:11 ` Zheng Liu
2013-01-23 9:42 ` Jan Kara
2013-01-18 12:00 ` [PATCH 04/12] ext4: Disable merging of uninitialized extents Jan Kara
2013-01-24 9:49 ` Dmitry Monakhov
2013-01-24 15:12 ` Jan Kara
2013-01-24 15:32 ` Dmitry Monakhov
2013-01-28 14:36 ` Theodore Ts'o
2013-01-28 15:02 ` Dmitry Monakhov
2013-01-28 15:38 ` Theodore Ts'o
2013-01-29 7:41 ` Dmitry Monakhov
2013-01-29 8:37 ` Zheng Liu
2013-01-31 7:47 ` Dmitry Monakhov
2013-01-31 12:39 ` Jan Kara [this message]
2013-01-31 14:09 ` Dmitry Monakhov
2013-01-31 16:54 ` Theodore Ts'o
2013-02-09 17:10 ` REGRESSION: " Theodore Ts'o
2013-02-12 21:58 ` Jan Kara
2013-02-13 4:57 ` Theodore Ts'o
2013-02-13 7:26 ` Dmitry Monakhov
2013-02-13 15:08 ` Merge window planning for ext4 and Ted's vacation Theodore Ts'o
2013-02-14 10:47 ` REGRESSION: [PATCH 04/12] ext4: Disable merging of uninitialized extents Jan Kara
2013-02-14 16:11 ` Jan Kara
2013-02-14 19:05 ` Theodore Ts'o
2013-02-14 21:32 ` Jan Kara
2013-01-18 12:00 ` [PATCH 05/12] ext4: Remove unnecessary wait for extent conversion in ext4_fallocate() Jan Kara
2013-01-18 12:00 ` [PATCH 06/12] ext4: Move work from io_end to inode Jan Kara
2013-01-28 14:45 ` Theodore Ts'o
2013-01-18 12:00 ` [PATCH 07/12] ext4: Simplify list handling in ext4_do_flush_completed_IO() Jan Kara
2013-01-28 14:51 ` Theodore Ts'o
2013-01-18 12:00 ` [PATCH 08/12] ext4: Remove __ext4_journalled_writepage() from mpage_da_submit_io() Jan Kara
2013-01-28 14:40 ` Theodore Ts'o
2013-01-18 12:00 ` [PATCH 09/12] ext4: Dirty page has always buffers attached Jan Kara
2013-01-28 17:55 ` Theodore Ts'o
2013-01-18 12:00 ` [PATCH 10/12] ext4: Simplify mpage_add_bh_to_extent() Jan Kara
2013-01-28 18:06 ` Theodore Ts'o
2013-01-18 12:00 ` [PATCH 11/12] ext4: Make ext4_bio_writepage() handle unprepared buffers Jan Kara
2013-01-29 1:59 ` Theodore Ts'o
2013-01-18 12:00 ` [PATCH 12/12] ext4: Fix ext4_writepage() to achieve data=ordered guarantees Jan Kara
2013-01-29 2:08 ` Theodore Ts'o
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