Patch "ext4: prevent data corruption with journaling + 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 journaling + 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-journaling-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 11:54:08 -0400
Subject: ext4: prevent data corruption with journaling + DAX

From: Ross Zwisler <[email protected]>

commit e9072d859df3e0f2c3ba450f0d1739595c2d5d13 upstream.

The current code has the potential for data corruption when changing an inode's journaling mode, as that can result in a subsequent unsafe change in S_DAX.

I've captured an instance of this data corruption in the following fstest:

https://patchwork.kernel.org/patch/9948377/

Prevent this data corruption from happening by disallowing changes to the journaling mode if the '-o dax' mount option was used. This means that for a given filesystem we could have a mix of inodes using either DAX or data journaling, but whatever state the inodes are in will be held for the duration of the mount.

---
 fs/ext4/inode.c |    5 -----
 fs/ext4/ioctl.c |   16 +++++++++++++---
 2 files changed, 13 insertions(+), 8 deletions(-)

@@ -5967,11 +5967,6 @@ int ext4_change_inode_journal_flag(struc
 		ext4_clear_inode_flag(inode, EXT4_INODE_JOURNAL_DATA);
 	}
 	ext4_set_aops(inode);
-	/*
-	 * Update inode->i_flags after EXT4_INODE_JOURNAL_DATA was updated.
-	 * E.g. S_DAX may get cleared / set.
-	 */
-	ext4_set_inode_flags(inode);
 
 	jbd2_journal_unlock_updates(journal);
 	percpu_up_write(&sbi->s_journal_flag_rwsem);

@@ -291,10 +291,20 @@ flags_err:
 	if (err)
 		goto flags_out;
 
-	if ((jflag ^ oldflags) & (EXT4_JOURNAL_DATA_FL))
+	if ((jflag ^ oldflags) & (EXT4_JOURNAL_DATA_FL)) {
+		/*
+		 * Changes to the journaling mode can cause unsafe changes to
+		 * S_DAX if we are using the DAX mount option.
+		 */
+		if (test_opt(inode->i_sb, DAX)) {
+			err = -EBUSY;
+			goto flags_out;
+		}
+
 		err = ext4_change_inode_journal_flag(inode, jflag);
-	if (err)
-		goto flags_out;
+		if (err)
+			goto flags_out;
+	}
 	if (migrate) {
 		if (flags & EXT4_EXTENTS_FL)
 			err = ext4_ext_migrate(inode);

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