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>

1 files changed, 10 insertions, 2 deletions

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 510dba785db4..eb4ddfeeeedc 100644
--- 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);
         }