Drop temporary tablespace hang with "enq: TS - contention"

When i drop the temporary tablespace, the SQL command hangs.

After further check, it waits for "enq: TS - contention".

SQL> select sid,event,seconds_in_wait from v$session where username='DONGHUA' and status='ACTIVE';

       SID EVENT                                    SECONDS_IN_WAIT
---------- ---------------------------------------- ---------------
        44 enq: TS - contention                                  21

And blocked by "SMON".

SQL> select * from v$lock where request>0;

ADDR     KADDR           SID TY        ID1        ID2      LMODE    REQUEST
-------- -------- ---------- -- ---------- ---------- ---------- ----------
     CTIME      BLOCK
---------- ----------
3E68104C 3E681078         44 TS          7          1          0          6
        29          0


SQL> select sid from v$lock where id1=7 and id2=1;

       SID
----------
        13
        44

SQL> select program,status from v$session where sid=13;

PROGRAM                                          STATUS
------------------------------------------------ --------
oracle@vmxdb01.lab.dbaglobe.com (SMON)           ACTIVE

SQL> select sid,event,seconds_in_wait from v$session where sid=13;

       SID EVENT                                    SECONDS_IN_WAIT
---------- ---------------------------------------- ---------------
        13 smon timer                                            87

Check which session is still using the "TEMP2"

SQL> SELECT se.username username,
  2  se.SID sid, se.serial# serial#,
  3  se.status status, se.sql_hash_value,
  4  se.prev_hash_value,se.machine machine,
  5  su.TABLESPACE tablespace,su.segtype,
  6  su.CONTENTS CONTENTS
  7  FROM v$session se,
  8  v$sort_usage su
  9  WHERE se.saddr=su.session_addr;

USERNAME                              SID    SERIAL# STATUS   SQL_HASH_VALUE
------------------------------ ---------- ---------- -------- --------------
PREV_HASH_VALUE MACHINE
--------------- ----------------------------------------------------------------
TABLESPACE                      SEGTYPE   CONTENTS
------------------------------- --------- ---------
DONGHUA                                41        259 INACTIVE              0
     2640221370 WORKGROUP\ORACLE-PC
TEMP2                           LOB_DATA  TEMPORARY

After kill it, the problem resloved.

SQL> alter system kill session '41,259';

System altered.