linux-kernel - Re: [PATCH v4 2/9] x86: support kmap_atomic_pfn

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Message-ID: <20150610151100.GA12757@lst.de>
Date:	Wed, 10 Jun 2015 17:11:00 +0200
From:	Christoph Hellwig <hch@....de>
To:	Matthew Wilcox <willy@...ux.intel.com>
Cc:	Dan Williams <dan.j.williams@...el.com>,
	linux-kernel@...r.kernel.org, axboe@...nel.dk, boaz@...xistor.com,
	david@...morbit.com, linux-arch@...r.kernel.org, arnd@...db.de,
	ross.zwisler@...ux.intel.com, linux-nvdimm@...ts.01.org,
	benh@...nel.crashing.org, linux-fsdevel@...r.kernel.org,
	heiko.carstens@...ibm.com, tj@...nel.org, paulus@...ba.org,
	hpa@...or.com, schwidefsky@...ibm.com, akpm@...ux-foundation.org,
	torvalds@...ux-foundation.org, mingo@...nel.org
Subject: Re: [PATCH v4 2/9] x86: support kmap_atomic_pfn_t() for persistent
	memory

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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