ext4: protect extent conversion after DIO with i_dio_count

Make sure extent conversion after DIO happens while i_dio_count is
still elevated so that inode_dio_wait() waits until extent conversion
is done.  This removes the need for explicit waiting for extent
conversion in some cases.

Reviewed-by: Zheng Liu <wenqing.lz@taobao.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 510dba785db45f376812ea5d044f40b19382b5da..eb4ddfeeeedca899a9a66849b4adf189a4cd9ce2 100644 (file)
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3036,11 +3036,18 @@ static ssize_t ext4_ext_direct_IO(int rw, struct kiocb *iocb,
 
        BUG_ON(iocb->private == NULL);
 
+       /*
+        * Make all waiters for direct IO properly wait also for extent
+        * conversion. This also disallows race between truncate() and
+        * overwrite DIO as i_dio_count needs to be incremented under i_mutex.
+        */
+       if (rw == WRITE)
+               atomic_inc(&inode->i_dio_count);
+
        /* If we do a overwrite dio, i_mutex locking can be released */
        overwrite = *((int *)iocb->private);
 
        if (overwrite) {
-               atomic_inc(&inode->i_dio_count);
                down_read(&EXT4_I(inode)->i_data_sem);
                mutex_unlock(&inode->i_mutex);
        }
@@ -3143,9 +3150,10 @@ static ssize_t ext4_ext_direct_IO(int rw, struct kiocb *iocb,
        }
 
 retake_lock:
+       if (rw == WRITE)
+               inode_dio_done(inode);
        /* take i_mutex locking again if we do a ovewrite dio */
        if (overwrite) {
-               inode_dio_done(inode);
                up_read(&EXT4_I(inode)->i_data_sem);
                mutex_lock(&inode->i_mutex);
        }