Re: [PATCH v4 2/9] x86: support kmap_atomic_pfn_t() for persistent memory

[Christoph Hellwig]

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.
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