dax: check for QUEUE_FLAG_DAX in bdev_dax_supported()

Add an explicit check for QUEUE_FLAG_DAX to __bdev_dax_supported().  This
is needed for DM configurations where the first element in the dm-linear or
dm-stripe target supports DAX, but other elements do not.  Without this
check __bdev_dax_supported() will pass for such devices, letting a
filesystem on that device mount with the DAX option.
Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Suggested-by: Mike Snitzer <snitzer@redhat.com>
Fixes: commit 545ed20e ("dm: add infrastructure for DAX support")
Cc: stable@vger.kernel.org
Acked-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Toshi Kani <toshi.kani@hpe.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/dax/super.c

@@ -86,6 +86,7 @@ bool __bdev_dax_supported(struct block_device *bdev, int blocksize)
 {
 	struct dax_device *dax_dev;
 	bool dax_enabled = false;
+	struct request_queue *q;
 	pgoff_t pgoff;
 	int err, id;
 	void *kaddr;
@@ -99,6 +100,13 @@ bool __bdev_dax_supported(struct block_device *bdev, int blocksize)
 		return false;
 	}
 
+	q = bdev_get_queue(bdev);
+	if (!q || !blk_queue_dax(q)) {
+		pr_debug("%s: error: request queue doesn't support dax\n",
+				bdevname(bdev, buf));
+		return false;
+	}
+
 	err = bdev_dax_pgoff(bdev, 0, PAGE_SIZE, &pgoff);
 	if (err) {
 		pr_debug("%s: error: unaligned partition for dax\n",