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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>,
        Jens Axboe <axboe@kernel.dk>, Boaz Harrosh <boaz@plexistor.com>,
        david <david@fromorbit.com>, linux-arch@vger.kernel.org,
        Arnd Bergmann <arnd@arndb.de>,
        Ross Zwisler <ross.zwisler@linux.intel.com>,
        "linux-nvdimm@lists.01.org" <linux-nvdimm@ml01.01.org>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Heiko Carstens <heiko.carstens@de.ibm.com>, Tejun Heo <tj@kernel.org>,
        Paul Mackerras <paulus@samba.org>, "H. Peter Anvin" <hpa@zytor.com>,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        "torvalds@linux-foundation.org" <torvalds@linux-foundation.org>,
        Ingo Molnar <mingo@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.
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