branch b1_6

b=17505

remove "mfd" from "cloing_list" for the "mfd" will be freed in mds_mfd_close

i=robert.read

lustre/mds/handler.c

@@ -492,6 +492,7 @@ static int mds_destroy_export(struct obd_export *export)
                  * is_orphan race, mds_mfd_close drops it */
                 MDS_DOWN_WRITE_ORPHAN_SEM(mfd->mfd_dentry->d_inode);
 
+                list_del_init(&mfd->mfd_list);
                 rc = mds_mfd_close(NULL, REQ_REC_OFF, obd, mfd,
                                    !(export->exp_flags & OBD_OPT_FAILOVER),
                                    lmm, lmm_size, logcookies,