Patch "ext4: prevent data corruption with inline data + DAX" has been added to the 4.14-stable tree

This is a note to let you know that I've just added the patch titled

ext4: prevent data corruption with inline data + DAX

to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
ext4-prevent-data-corruption-with-inline-data-dax.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Ross Zwisler <[email protected]>
Date: Thu, 12 Oct 2017 11:52:34 -0400
Subject: ext4: prevent data corruption with inline data + DAX

From: Ross Zwisler <[email protected]>

commit 559db4c6d784ceedc2a5418ced4d357cb843e221 upstream.

If an inode has inline data it is currently prevented from using DAX by a check in ext4_set_inode_flags(). When the inode grows inline data via ext4_create_inline_data() or removes its inline data via ext4_destroy_inline_data_nolock(), the value of S_DAX can change.

Currently these changes are unsafe because we don't hold off page faults and I/O, write back dirty radix tree entries and invalidate all mappings. There are also issues with mm-level races when changing the value of S_DAX, as well as issues with the VM_MIXEDMAP flag:

https://www.spinics.net/lists/linux-xfs/msg09859.html

The unsafe transition of S_DAX can reliably cause data corruption, as shown by the following fstest:

https://patchwork.kernel.org/patch/9948381/

Fix this issue by preventing the DAX mount option from being used on filesystems that were created to support inline data. Inline data is an option given to mkfs.ext4.

---
 fs/ext4/inline.c |   10 ----------
 fs/ext4/super.c  |    5 +++++
 2 files changed, 5 insertions(+), 10 deletions(-)

@@ -302,11 +302,6 @@ static int ext4_create_inline_data(handl
 	EXT4_I(inode)->i_inline_size = len + EXT4_MIN_INLINE_DATA_SIZE;
 	ext4_clear_inode_flag(inode, EXT4_INODE_EXTENTS);
 	ext4_set_inode_flag(inode, EXT4_INODE_INLINE_DATA);
-	/*
-	 * Propagate changes to inode->i_flags as well - e.g. S_DAX may
-	 * get cleared
-	 */
-	ext4_set_inode_flags(inode);
 	get_bh(is.iloc.bh);
 	error = ext4_mark_iloc_dirty(handle, inode, &is.iloc);
 

@@ -451,11 +446,6 @@ static int ext4_destroy_inline_data_nolo
 		}
 	}
 	ext4_clear_inode_flag(inode, EXT4_INODE_INLINE_DATA);
-	/*
-	 * Propagate changes to inode->i_flags as well - e.g. S_DAX may
-	 * get set.
-	 */
-	ext4_set_inode_flags(inode);
 
 	get_bh(is.iloc.bh);
 	error = ext4_mark_iloc_dirty(handle, inode, &is.iloc);

@@ -3708,6 +3708,11 @@ static int ext4_fill_super(struct super_
 	}
 
 	if (sbi->s_mount_opt & EXT4_MOUNT_DAX) {
+		if (ext4_has_feature_inline_data(sb)) {
+			ext4_msg(sb, KERN_ERR, "Cannot use DAX on a filesystem"
+					" that may contain inline data");
+			goto failed_mount;
+		}
 		err = bdev_dax_supported(sb, blocksize);
 		if (err)
 			goto failed_mount;

Patches currently in stable-queue which might be from [email protected] are

queue-4.14/ext4-prevent-data-corruption-with-journaling-dax.patch queue-4.14/ext4-prevent-data-corruption-with-inline-data-dax.patch