quota: add missing use of dq_data_lock in __dquot_initialize

The bulk of __dquot_initialize runs under the dqptr_sem which
protects the inode->i_dquot pointers. It doesn't protect the
dereferenced contents, though. Those are protected by the
dq_data_lock, which is missing around the dquot_resv_space call.
Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/quota/dquot.c

@@ -1439,8 +1439,11 @@ static void __dquot_initialize(struct inode *inode, int type)
 			 * did a write before quota was turned on
 			 */
 			rsv = inode_get_rsv_space(inode);
-			if (unlikely(rsv))
+			if (unlikely(rsv)) {
+				spin_lock(&dq_data_lock);
 				dquot_resv_space(inode->i_dquot[cnt], rsv);
+				spin_unlock(&dq_data_lock);
+			}
 		}
 	}
 out_err: