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Re: [PATCH 0/4] Fix filesystem freezing

To: Jan Kara <jack@xxxxxxx>
Subject: Re: [PATCH 0/4] Fix filesystem freezing
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Thu, 12 Jan 2012 13:48:41 +1100
Cc: linux-fsdevel@xxxxxxxxxxxxxxx, LKML <linux-kernel@xxxxxxxxxxxxxxx>, linux-ext4@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, Eric Sandeen <sandeen@xxxxxxxxxxx>, Dave Chinner <dchinner@xxxxxxxxxx>, Surbhi Palande <csurbhi@xxxxxxxxx>, Kamal Mostafa <kamal@xxxxxxxxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>
In-reply-to: <1326331253-6497-1-git-send-email-jack@xxxxxxx>
References: <1326331253-6497-1-git-send-email-jack@xxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
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....


Dave Chinner

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