Re: [PATCH v2 2/5] ext4: prevent data corruption with journaling + DAX

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(a)linux.intel.com&gt; Suggested-by: Jan Kara <jack(a)suse.cz&gt;

--- fs/ext4/inode.c | 5 ----- fs/ext4/ioctl.c | 16 +++++++++++++--- 2 files changed, 13 insertions(+), 8 deletions(-) diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index e963508..3207333 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -5971,11 +5971,6 @@ int ext4_change_inode_journal_flag(struct inode *inode, int val) 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); diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c index afb66d4..b0b754b 100644 --- a/fs/ext4/ioctl.c +++ b/fs/ext4/ioctl.c @@ -290,10 +290,20 @@ static int ext4_ioctl_setflags(struct inode *inode, 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); -- 2.9.5