[PATCH 4.2 052/258] blockdev: dont set S_DAX for misaligned partitions

[Greg Kroah-Hartman]

4.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jeff Moyer <jmoyer@xxxxxxxxxx>

commit f0b2e563bc419df7c1b3d2f494574c25125f6aed upstream.

The dax code doesn't currently support misaligned partitions,
so disable O_DIRECT via dax until such time as that support
materializes.

Suggested-by: Boaz Harrosh <boaz@xxxxxxxxxxxxx>
Signed-off-by: Jeff Moyer <jmoyer@xxxxxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 fs/block_dev.c |    7 +++++++
 1 file changed, 7 insertions(+)

--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1241,6 +1241,13 @@ static int __blkdev_get(struct block_dev
 				goto out_clear;
 			}
 			bd_set_size(bdev, (loff_t)bdev->bd_part->nr_sects << 9);
+			/*
+			 * If the partition is not aligned on a page
+			 * boundary, we can't do dax I/O to it.
+			 */
+			if ((bdev->bd_part->start_sect % (PAGE_SIZE / 512)) ||
+			    (bdev->bd_part->nr_sects % (PAGE_SIZE / 512)))
+				bdev->bd_inode->i_flags &= ~S_DAX;
 		}
 	} else {
 		if (bdev->bd_contains == bdev) {


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