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From: Ross Zwisler <>
To: Toshi Kani <>,
	Mike Snitzer <>,
	Ross Zwisler <>
Subject: [PATCH 3/7] dm: fix test for DAX device support
Date: Thu, 24 May 2018 20:55:14 -0600	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

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.

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.

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.

Signed-off-by: Ross Zwisler <>
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)

  parent reply	other threads:[~2018-05-25  2:55 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-25  2:55 [PATCH 0/7] Fix DM DAX handling Ross Zwisler
2018-05-25  2:55 ` [PATCH 1/7] fs: allow per-device dax status checking for filesystems Ross Zwisler
2018-05-25  5:02   ` Darrick J. Wong
2018-05-25 15:42     ` Ross Zwisler
2018-05-25 19:23       ` Darrick J. Wong
2018-05-26 14:07   ` kbuild test robot
2018-05-25  2:55 ` [PATCH 2/7] dax: change bdev_dax_supported() to support boolean returns Ross Zwisler
2018-05-25  5:01   ` Darrick J. Wong
2018-05-25  2:55 ` Ross Zwisler [this message]
2018-05-25  2:55 ` [PATCH 4/7] dm: prevent DAX mounts if not supported Ross Zwisler
2018-05-25 19:54   ` Mike Snitzer
2018-05-25 21:36     ` Ross Zwisler
2018-05-25  2:55 ` [PATCH 5/7] dm: remove DM_TYPE_DAX_BIO_BASED dm_queue_mode Ross Zwisler
2018-05-25  2:55 ` [PATCH 6/7] dm-snap: remove unnecessary direct_access() stub Ross Zwisler
2018-05-25  2:55 ` [PATCH 7/7] dm-error: " Ross Zwisler

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