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From: Mike Snitzer <snitzer@redhat.com>
To: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Toshi Kani <toshi.kani@hpe.com>,
	dm-devel@redhat.com, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-nvdimm@lists.01.org,
	linux-xfs@vger.kernel.org
Subject: Re: [PATCH v2 3/7] dm: fix test for DAX device support
Date: Fri, 1 Jun 2018 16:19:25 -0400	[thread overview]
Message-ID: <20180601201924.GA1144@redhat.com> (raw)
In-Reply-To: <20180529195106.14268-4-ross.zwisler@linux.intel.com>

On Tue, May 29 2018 at  3:51P -0400,
Ross Zwisler <ross.zwisler@linux.intel.com> wrote:

> Currently device_supports_dax() just checks to see if the QUEUE_FLAG_DAX
> flag is set on the device's request queue to decide whether or not the
> device supports filesystem DAX.  This is insufficient because there are
> devices like PMEM namespaces in raw mode which have QUEUE_FLAG_DAX set but
> which don't actually support DAX.

Isn't that a PMEM bug then?

What is the point of setting QUEUE_FLAG_DAX if it cannot be trusted?
 
> This means that you could create a dm-linear device, for example, where the
> first part of the dm-linear device was a PMEM namespace in fsdax mode and
> the second part was a PMEM namespace in raw mode.  Both DM and the
> filesystem you put on that dm-linear device would think the whole device
> supports DAX, which would lead to bad behavior once your raw PMEM namespace
> part using DAX needed struct page for something.

The PMEM namespace in raw mode shouldn't be setting QUEUE_FLAG_DAX, if
it didn't then the stacked-up linear DM wouldn't 

> Fix this by using bdev_dax_supported() like filesystems do at mount time.
> This checks for raw mode and also performs other tests like checking to
> make sure the dax_direct_access() path works.

Sorry "This" does those things where?

> 
> Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> Fixes: commit 545ed20e6df6 ("dm: add infrastructure for DAX support")
> ---
>  drivers/md/dm-table.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> index 0589a4da12bb..5bb994b012ca 100644
> --- a/drivers/md/dm-table.c
> +++ b/drivers/md/dm-table.c
> @@ -885,9 +885,7 @@ EXPORT_SYMBOL_GPL(dm_table_set_type);
>  static int device_supports_dax(struct dm_target *ti, struct dm_dev *dev,
>  			       sector_t start, sector_t len, void *data)
>  {
> -	struct request_queue *q = bdev_get_queue(dev->bdev);
> -
> -	return q && blk_queue_dax(q);
> +	return bdev_dax_supported(dev->bdev, PAGE_SIZE);
>  }
>  
>  static bool dm_table_supports_dax(struct dm_table *t)
> -- 
> 2.14.3
> 

  reply	other threads:[~2018-06-01 20:19 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-29 19:50 [PATCH v2 0/7] Fix DM DAX handling Ross Zwisler
2018-05-29 19:51 ` [PATCH v2 1/7] fs: allow per-device dax status checking for filesystems Ross Zwisler
2018-05-29 19:51 ` [PATCH v2 2/7] dax: change bdev_dax_supported() to support boolean returns Ross Zwisler
2018-05-29 21:25   ` Darrick J. Wong
2018-05-29 22:01     ` Ross Zwisler
2018-05-31 19:13       ` Darrick J. Wong
2018-05-31 20:34         ` Ross Zwisler
2018-05-31 20:35         ` Dan Williams
2018-05-31 20:41         ` Ross Zwisler
2018-05-31 20:52         ` Mike Snitzer
2018-05-31 22:26           ` [dm-devel] " Darrick J. Wong
2018-06-01 20:59             ` Ross Zwisler
2018-06-01  1:26         ` Dave Chinner
2018-06-01  1:57           ` Dan Williams
2018-06-01  2:24             ` Dave Chinner
2018-06-01  4:02               ` Dan Williams
2018-06-03 22:20                 ` Dave Chinner
2018-06-04  0:25                   ` Dave Chinner
2018-06-04  1:48                     ` Dan Williams
2018-06-04 23:40                       ` Dan Williams
2018-06-05  0:33                         ` Mike Snitzer
2018-06-05  5:55                           ` Dave Chinner
2018-06-05  3:32                         ` Dan Williams
2018-05-29 19:51 ` [PATCH v2 3/7] dm: fix test for DAX device support Ross Zwisler
2018-06-01 20:19   ` Mike Snitzer [this message]
2018-06-01 20:46     ` Mike Snitzer
2018-06-01 21:11       ` Ross Zwisler
2018-06-01 21:16       ` Dan Williams
2018-05-29 19:51 ` [PATCH v2 4/7] dm: prevent DAX mounts if not supported Ross Zwisler
2018-06-01 21:55   ` Mike Snitzer
2018-06-04 23:15     ` Ross Zwisler
2018-06-20 15:17       ` Mike Snitzer
2018-06-25 19:20         ` Ross Zwisler
2018-05-29 19:51 ` [PATCH v2 5/7] dm: remove DM_TYPE_DAX_BIO_BASED dm_queue_mode Ross Zwisler
2018-06-01 22:04   ` Mike Snitzer
2018-06-04 23:24     ` Ross Zwisler
2018-06-04 23:49       ` Kani, Toshi
2018-06-05  0:46       ` Mike Snitzer
2018-06-06 17:24         ` Ross Zwisler
2018-06-06 22:29           ` Mike Snitzer
2018-05-29 19:51 ` [PATCH v2 6/7] dm-snap: remove unnecessary direct_access() stub Ross Zwisler
2018-05-29 19:51 ` [PATCH v2 7/7] dm-error: " Ross Zwisler

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