linux-kernel - reproducer for DM on MD flush deadlock? (was: Re: [PULL REQUEST] md bug fixes)

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Message-ID: <AANLkTi=H3-GrEZVWzmHyHvyx93HU6x=t_n6TBqCiEwxX@mail.gmail.com>
Date:	Fri, 17 Dec 2010 13:13:47 -0500
From:	Mike Snitzer <snitzer@...hat.com>
To:	Neil Brown <neilb@...e.de>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org,
	dm-devel@...hat.com
Subject: reproducer for DM on MD flush deadlock? (was: Re: [PULL REQUEST] md
 bug fixes)

On Tue, Dec 14, 2010 at 2:22 AM, Neil Brown <neilb@...e.de> wrote:
>
>
> Hi Linus,
>  here are a few bug fixes for md.
>  Some of the patches are actually clean-up rather than bug-fix,
>  but I that make the bugfix simpler to review.
>
> Thanks,
> NeilBrown
>
>
> The following changes since commit 6313e3c21743cc88bb5bd8aa72948ee1e83937b6:
>
>  Merge branches 'x86-fixes-for-linus', 'perf-fixes-for-linus' and 'sched-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip (2010-12-08 06:40:59 -0800)
>
> are available in the git repository at:
>
>  git://neil.brown.name/md/ for-linus
>
> NeilBrown (5):
>      md: remove handling of flush_pending in md_submit_flush_data
>      md: move code in to submit_flushes.
>      md: fix possible deadlock in handling flush requests.

Hi Neil,

Thanks for fixing this DM on MD flush issue.  But my attempts to
reproduce it have been unsuccessful.

I've tried ext4 w/ barriers to a DM device above a 2 member MD RAID1.
The DM device has a table with 2 linear targets to the same md0
device:

# dmsetup table
multiple_targets: 0 24576 linear 9:0 2048
multiple_targets: 24576 49152 linear 9:0 26624

No amount of IO with flushes has enabled me to hit a deadlock (in
md_flush_request,  md_write_start, etc).

Do you have a simple reproducer for this issue?

Mike
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