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Date: Wed, 10 Jun 2015 09:17:40 -0700
Message-ID: <CAPcyv4hC1ud_xhZpqDALMbijrjU4GSBHscqTmPoimHn4hX8anQ@mail.gmail.com>
Subject: Re: [PATCH v4 2/9] x86: support kmap_atomic_pfn_t() for persistent memory
From: Dan Williams <dan.j.williams@intel.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Matthew Wilcox <willy@linux.intel.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
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On Wed, Jun 10, 2015 at 9:11 AM, Christoph Hellwig <hch@lst.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.