Re: [PATCH v2 9/9] devm_memremap_pages: protect against pmem device unbind

On Wed, 2015-08-26 at 14:46 +0200, Christoph Hellwig wrote: > On Tue, Aug 25, 2015 at 09:28:13PM -0400, Dan Williams wrote: > > Given that: > > > > 1/ device ->remove() can not be failed > > > > 2/ a pmem device may be unbound at any time > > > > 3/ we do not know what other parts of the kernel are actively using a > > 'struct page' from devm_memremap_pages() > > > > ...provide a facility for active usages of device memory to block pmem > > device unbind. With a percpu_ref it should be feasible to take a > > reference on a per-I/O or other high frequency basis. > > Without a caller of get_page_map this is just adding dead code. I'd > suggest to group it in a series with that caller. > Agreed, we can drop this until the first user arrives. > Also if the page_map gets exposed in a header the name is a bit too generic. > memremap_map maybe? Done, and in the patch below I hide the internal implementation details of page_map in kernel/memremap.c and only expose the percpu_ref in the public memremap_map.