Query on v$asm_diskgroup Hangs

Due to underneath SAN LUN issue, after manually dismounting problem disk group, the queries on v$asm_* views hang forever.

1)  Check blocking sessions, and find blocking session is SID=426, and the final blocking session SID=392.

SQL> select SID,LAST_CALL_ET,EVENT,BLOCKING_SESSION,FINAL_BLOCKING_SESSION 
from v$session where BLOCKING_SESSION is not null;

SID LAST_CALL_ET  EVENT         BLOCKING_SESSION FINAL_BLOCKING_SESSION
 12  2313        enq: DD - contention       426        392
 17  9526        enq: DD - contention       426        392
 23  7726        enq: DD - contention       426        392
 25  527598      enq: DD - contention       426        392
 40  384765      enq: DD - contention       426        392
 418 132675      enq: DD - contention       426        392
 425 3397        enq: DD - contention       426        392
 426 530330      rdbms ipc reply            392        392
 444 15982       enq: DD - contention       426        392

...
..
.

2) Check what is session SID=392, which is ASM RBAL background process.

SQL> select s.sid,p.SPID,p.PNAME,p.BACKGROUND 
       from v$process p, v$session s 
      where s.PADDR=p.ADDR and s.sid in ( 426, 392);

SID        SPID                     PNAME B
---------- ------------------------ ----- -
 392       11670                    RBAL  1
 426       24638

$ ps -eaf | grep 11670
grid 11670 1 0 Mar22 ? 00:11:26 asm_rbal_+ASM1

3) Check which processes are still holding dismounted disk group.

$ lsof | grep ASMD_TEST
oracleasm 1246 grid 4r BLK 253,10 0t0 18446612242469980264 /dev/oracleasm/disks/ASMD_TEST1
oracle_20 2087 grid 14r BLK 253,10 0t0 18446612242469980264 /dev/oracleasm/disks/ASMD_TEST1
oracle_33 3371 grid 14r BLK 253,10 0t0 18446612242469980264 /dev/oracleasm/disks/ASMD_TEST1
oracle_47 4754 grid 17r BLK 253,10 0t0 18446612242469980264 /dev/oracleasm/disks/ASMD_TEST1
...
..
.

$ fuser /dev/oracleasm/disks/ASMD_TEST1
/dev/oracleasm/disks/ASMD_TEST1: 1246 2087 3371 4754 ... ... ..

In this case, ASM instance bounce is required for resolving this issue.