Btrfs: correctly flush data on defrag when compression is enabled

When the defrag flag BTRFS_DEFRAG_RANGE_START_IO is set and compression
enabled, we weren't flushing completely, as writing compressed extents
is a 2 steps process, one to compress the data and another one to write
the compressed data to disk.
Signed-off-by: Filipe David Borba Manana <fdmanana@gmail.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>

fs/btrfs/ioctl.c

@@ -1382,8 +1382,12 @@ int btrfs_defrag_file(struct inode *inode, struct file *file,
 		}
 	}
 
-	if ((range->flags & BTRFS_DEFRAG_RANGE_START_IO))
+	if ((range->flags & BTRFS_DEFRAG_RANGE_START_IO)) {
 		filemap_flush(inode->i_mapping);
+		if (test_bit(BTRFS_INODE_HAS_ASYNC_EXTENT,
+			     &BTRFS_I(inode)->runtime_flags))
+			filemap_flush(inode->i_mapping);
+	}
 
 	if ((range->flags & BTRFS_DEFRAG_RANGE_COMPRESS)) {
 		/* the filemap_flush will queue IO into the worker threads, but