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Subject[PATCH v2 2/5] ext4: prevent data corruption with journaling + DAX
Date
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>
Suggested-by: Jan Kara <jack@suse.cz>
---
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
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