[PATCH 1/3] ext4: Add alignment check for DAX mount

[Toshi Kani]

When a partition is not aligned by 4KB, mount -o dax succeeds,
but any read/write access to the filesystem fails, except for
metadata update.

Add alignment check to ext4_fill_super() when -o dax is specified.

Reported-by: Micah Parrish <micah.parrish@xxxxxxx>
Signed-off-by: Toshi Kani <toshi.kani@xxxxxxx>
Cc: "Theodore Ts'o" <tytso@xxxxxxx>
Cc: Andreas Dilger <adilger.kernel@xxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
---
 fs/ext4/super.c |    6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 304c712..90a8670 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3421,6 +3421,12 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 					"error: unsupported blocksize for dax");
 			goto failed_mount;
 		}
+		if (sb->s_bdev->bd_part->start_sect % (PAGE_SIZE / 512) ||
+		    sb->s_bdev->bd_part->nr_sects % (PAGE_SIZE / 512)) {
+			ext4_msg(sb, KERN_ERR,
+					"error: unaligned partition for dax");
+			goto failed_mount;
+		}
 		if (!sb->s_bdev->bd_disk->fops->direct_access) {
 			ext4_msg(sb, KERN_ERR,
 					"error: device does not support dax");