From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v4 2/9] x86: support kmap_atomic_pfn_t() for persistent
	memory
Date: Wed, 10 Jun 2015 17:11:00 +0200
Message-ID: <20150610151100.GA12757@lst.de>
References: <20150605205052.20751.77149.stgit@dwillia2-desk3.amr.corp.intel.com> <20150605211912.20751.35406.stgit@dwillia2-desk3.amr.corp.intel.com> <20150610121202.GA9190@lst.de> <20150610150334.GK2729@linux.intel.com>
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Cc: Dan Williams <dan.j.williams@intel.com>,
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	david@fromorbit.com, linux-arch@vger.kernel.org, arnd@arndb.de,
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To: Matthew Wilcox <willy@linux.intel.com>
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On Wed, Jun 10, 2015 at 11:03:35AM -0400, Matthew Wilcox wrote:
> On Wed, Jun 10, 2015 at 02:12:02PM +0200, Christoph Hellwig wrote:
> > Btw, I don't think this actually is safe without refcounting your kmap
> > structure.
> > 
> > The driver model ->remove callback can be called at any time, which
> > will ioremap the memory and remap the kmap structure.  But at this
> > point a user might still be using it.
> 
> Won't the device data structures be pinned by the refcount on the bdev?

An open filesystem only keeps a reference on the request_queue.  The
underlying driver model ->remove method will still be called on
a surprise removal.