ext4_double_down_write_data_sem
extern void ext4_double_down_write_data_sem(struct inode *first,
ext4_double_down_write_data_sem(inode, inode_bl);
ext4_double_down_write_data_sem(orig_inode, donor_inode);
ext4_double_down_write_data_sem(orig_inode, donor_inode);