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%3Ba=su...

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 stable@vger.kernel.org know about it.

From e9072d859df3e0f2c3ba450f0d1739595c2d5d13 Mon Sep 17 00:00:00 2001

From: Ross Zwisler ross.zwisler@linux.intel.com Date: Thu, 12 Oct 2017 11:54:08 -0400 Subject: ext4: prevent data corruption with journaling + DAX

From: Ross Zwisler ross.zwisler@linux.intel.com

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.

Signed-off-by: Ross Zwisler ross.zwisler@linux.intel.com Signed-off-by: Theodore Ts'o tytso@mit.edu Reviewed-by: Jan Kara jack@suse.cz Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

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

--- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -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); --- a/fs/ext4/ioctl.c +++ b/fs/ext4/ioctl.c @@ -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 ross.zwisler@linux.intel.com are

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