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

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Date:	Wed, 10 Jun 2015 09:17:40 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Christoph Hellwig <hch@....de>
Cc:	Matthew Wilcox <willy@...ux.intel.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jens Axboe <axboe@...nel.dk>,
	Boaz Harrosh <boaz@...xistor.com>, david <david@...morbit.com>,
	linux-arch@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
	Ross Zwisler <ross.zwisler@...ux.intel.com>,
	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Tejun Heo <tj@...nel.org>, Paul Mackerras <paulus@...ba.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH v4 2/9] x86: support kmap_atomic_pfn_t() for persistent memory

On Wed, Jun 10, 2015 at 9:11 AM, Christoph Hellwig <hch@....de> wrote:
> On Wed, Jun 10, 2015 at 08:36:48AM -0700, Dan Williams wrote:
>> On surprise removal my expectation is that the driver keeps the the
>> ioremap mapping alive for at least a synchronize_rcu() period.  With
>> that in place the rcu_read_lock() in kmap_atomic_pfn_t() should keep
>> the mapping alive for the short duration, or otherwise prevent new
>> mappings.  However, I missed converting the driver to order its
>> iounmap() with respect to the pfn range registration via devres, will
>> fix.
>
> Right.  I guess the best idea is to replace devm_register_kmap_pfn_range
> with an interface that does the ioremap, in which case the cleanup
> function can take care of the proper ordering behind the drivers back.

Even better than what I was thinking... will do.
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