Re: [PATCH v4 10/12] dax: add struct iomap based DAX PMD support

[Christoph Hellwig]

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.