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[v4,3/5] ext4: Online defrag not supported with DAX

Message ID 1456167562-28576-4-git-send-email-ross.zwisler@linux.intel.com (mailing list archive)
State New, archived
Headers show

Commit Message

Ross Zwisler Feb. 22, 2016, 6:59 p.m. UTC
Online defrag operations for ext4 are hard coded to use the page cache.
See ext4_ioctl() -> ext4_move_extents() -> move_extent_per_page()

When combined with DAX I/O, which circumvents the page cache, this can
result in data corruption.  This was observed with xfstests ext4/307 and

Fix this by only allowing online defrag for non-DAX files.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Reviewed-by: Jan Kara <jack@suse.cz>
 fs/ext4/ioctl.c | 5 +++++
 1 file changed, 5 insertions(+)
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diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index a99b010..eae5917 100644
--- a/fs/ext4/ioctl.c
+++ b/fs/ext4/ioctl.c
@@ -583,6 +583,11 @@  group_extend_out:
 				 "Online defrag not supported with bigalloc");
 			err = -EOPNOTSUPP;
 			goto mext_out;
+		} else if (IS_DAX(inode)) {
+			ext4_msg(sb, KERN_ERR,
+				 "Online defrag not supported with DAX");
+			err = -EOPNOTSUPP;
+			goto mext_out;
 		err = mnt_want_write_file(filp);