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Date: Mon, 3 Oct 2016 18:37:54 +0200
From: Christoph Hellwig <hch@lst.de>
To: Jan Kara <jack@suse.cz>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>,
        linux-kernel@vger.kernel.org, "Theodore Ts'o" <tytso@mit.edu>,
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        Dan Williams <dan.j.williams@intel.com>,
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        linux-nvdimm@ml01.01.org, linux-xfs@vger.kernel.org
Subject: Re: [PATCH v4 10/12] dax: add struct iomap based DAX PMD support
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On Mon, Oct 03, 2016 at 12:59:49PM +0200, Jan Kara wrote:
> I'm not quite sure if it is OK to call ->iomap_begin() without ever calling
> ->iomap_end. Specifically the comment before iomap_apply() says:
> 
> "It is assumed that the filesystems will lock whatever resources they
> require in the iomap_begin call, and release them in the iomap_end call."
> 
> so what you do could result in unbalanced allocations / locks / whatever.
> Christoph?

Indeed.  For XFS we only rely on iomap_end for error handling at the
moment, but it is intended to be paired for locking, as cluster file
systems like gfs2 requested this.