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

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Message-ID: <20150827073325.GB27207@lst.de>
Date:	Thu, 27 Aug 2015 09:33:25 +0200
From:	"hch@....de" <hch@....de>
To:	"Williams, Dan J" <dan.j.williams@...el.com>
Cc:	"hch@....de" <hch@....de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mingo@...nel.org" <mingo@...nel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"hpa@...or.com" <hpa@...or.com>,
	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
	"ross.zwisler@...ux.intel.com" <ross.zwisler@...ux.intel.com>,
	"boaz@...xistor.com" <boaz@...xistor.com>,
	"david@...morbit.com" <david@...morbit.com>
Subject: Re: [PATCH v2 9/9] devm_memremap_pages: protect against pmem
	device unbind

On Wed, Aug 26, 2015 at 09:39:18PM +0000, Williams, Dan J wrote:
> 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.

Yes, that looks good once we're getting the users for it.
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