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Re: [regression, 3.0-rc] xfs: freeze hang in 068

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [regression, 3.0-rc] xfs: freeze hang in 068
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Mon, 11 Jul 2011 05:51:47 -0400
Cc: hch@xxxxxx, xfs@xxxxxxxxxxx
In-reply-to: <20110711010357.GD23038@dastard>
References: <20110711010357.GD23038@dastard>
User-agent: Mutt/1.5.21 (2010-09-15)
On Mon, Jul 11, 2011 at 11:03:57AM +1000, Dave Chinner wrote:
> Christoph,
> 
> The recent changes to the active transaction accounting to close a
> race on freeze can hang the freeze process and hence the filesystem.

That commit isn't in 3.0-rc, but I guess it's just the subject line
that is incorrect.

> So effective we cannot sleep waiting for SB_FREEZE_TRANS to go away
> while holding an active transaction reference because the freeze
> process does not set and check SB_FREEZE_TRANS/mp->m_active_trans
> atomically.
> 
> I haven't put any thought into how to solve this problem yet, so I'd
> suggest that at this late stage we need to revert 315fdfa (xfs: fix
> filesystsem freeze race in xfs_trans_alloc) because the race it
> fixes is far less critical (i.e. doesn't hang the filesystem) and
> harder to hit than the regression introduced here.

Yes, I guess we need to revert it for now.

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