From: Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v4 10/12] dax: add struct iomap based DAX PMD support
Date: Mon, 3 Oct 2016 18:37:54 +0200
Message-ID: <20161003163754.GB1496@lst.de>
References: <1475189370-31634-1-git-send-email-ross.zwisler@linux.intel.com> <1475189370-31634-11-git-send-email-ross.zwisler@linux.intel.com> <20161003105949.GP6457@quack2.suse.cz>
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Cc: Ross Zwisler <ross.zwisler@linux.intel.com>,
	linux-kernel@vger.kernel.org, Theodore Ts'o <tytso@mit.edu>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Andreas Dilger <adilger.kernel@dilger.ca>,
	Andrew Morton <akpm@linux-foundation.org>,
	Christoph Hellwig <hch@lst.de>,
	Dan Williams <dan.j.williams@intel.com>,
	Dave Chinner <david@fromorbit.com>, Jan Kara <jack@suse.com>,
	Matthew Wilcox <mawilcox@microsoft.com>, linux-ext4@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
	linux-nvdimm@lists.01.org, linux-xfs@vger.kernel.org
To: Jan Kara <jack@suse.cz>
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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.

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