linux-ext4 - Re: [PATCH 0/4] Fix filesystem freezing

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Message-ID: <20120112024841.GB2806@dastard>
Date:	Thu, 12 Jan 2012 13:48:41 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Jan Kara <jack@...e.cz>
Cc:	linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	linux-ext4@...r.kernel.org, xfs@....sgi.com,
	Eric Sandeen <sandeen@...deen.net>,
	Dave Chinner <dchinner@...hat.com>,
	Surbhi Palande <csurbhi@...il.com>,
	Kamal Mostafa <kamal@...onical.com>,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH 0/4] Fix filesystem freezing

On Thu, Jan 12, 2012 at 02:20:49AM +0100, Jan Kara wrote:
> 
>   Hello,
> 
>   filesystem freezing is currently racy and thus we can end up with dirty data
> on frozen filesystem (see changelog of the first patch for detailed race
> description and proposed fix). This patch series aims at fixing this.

It only fixes the dirty data race (i.e. SB_FREEZE_WRITE). The same
race conditions exist for SB_FREEZE_TRANS on XFS, and so need the
same fix. That race has had one previous attempt at fixing it in
XFS but that's not possible:

b2ce397 Revert "xfs: fix filesystsem freeze race in xfs_trans_alloc"
7a249cf xfs: fix filesystsem freeze race in xfs_trans_alloc

It was looking at that problem earlier today that lead to the
solution Eric proposed. Essentially the method in these patches
needs to replace the xfs specifc m_active_trans counter and delay
during ->fs_freeze to prevent that race condition....

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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