Re: [PATCH v2 7/7] mm, dax: unmap dax mappings at bdev shutdown

From: Dan Williams <dan.j.williams@intel.com>
To: "linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>
Cc: Dave Chinner <david@fromorbit.com>,
	linux-block@vger.kernel.org, Jan Kara <jack@suse.com>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH v2 7/7] mm, dax: unmap dax mappings at bdev shutdown
Date: Mon, 30 Nov 2015 20:21:29 -0800	[thread overview]
Message-ID: <CAPcyv4j4Hap+R_BeKnMhsT-Jxk1Dx=4hvFMzvCUNgo8AcgEUxw@mail.gmail.com> (raw)
In-Reply-To: <CAPcyv4i6gvjzEEb0+ZdoRFGUDPXKj=_NLdyaZZi2pwXdyBUK9Q@mail.gmail.com>

On Mon, Nov 30, 2015 at 2:03 PM, Dan Williams <dan.j.williams@intel.com> wrote:
> On Wed, Nov 25, 2015 at 10:37 AM, Dan Williams <dan.j.williams@intel.com> wrote:
>> Currently dax mappings leak past / survive block_device shutdown.  While
>> page cache pages are permitted to be read/written after the block_device
>> is torn down this is not acceptable in the dax case as all media access
>> must end when the device is disabled.  The pfn backing a dax mapping is
>> permitted to be invalidated after bdev shutdown and this is indeed the
>> case with brd.
>>
>> When a dax capable block_device driver calls del_gendisk_queue() in its
>> shutdown path it needs to ensure that all DAX pfns are unmapped, and
>> that no new mappings can be established.  This is different than the
>> pagecache backed case where the disk is protected by the queue being
>> torn down which ends I/O to the device.  Since dax bypasses the page
>> cache we need to unconditionally unmap the inode.
>>
>> Cc: Jan Kara <jack@suse.com>
>> Cc: Dave Chinner <david@fromorbit.com>
>> Cc: Matthew Wilcox <willy@linux.intel.com>
>> Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
>> [honza: drop changes to truncate_inode_pages_final]
>> [honza: ensure mappings can't be re-established]
>> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
>> ---
>
> Dave, can this patch move forward while we figure out ->shutdown() for
> super_operations?

Disregard, I'm straightened out now.