Alert logfile reported as below: 

*********************
Wed May 27 13:11:47 2009
Errors in file /u01/app/oracle/admin/proa021/udump/proa021_ora_9533.trc:
ORA-07445: exception encountered: core dump [memset()+116] [SIGSEGV] [Address not mapped to object] [0] [] []

From Trace file
********************
Dump file /u01/app/oracle/admin/proa021/udump/proa021_ora_9533.trc

Oracle8i Enterprise Edition Release 8.1.7.4.0 - Production
With the Partitioning option
JServer Release 8.1.7.4.0 - Production
ORACLE_HOME = /u01/app/oracle/product/817proa021
System name:	SunOS
Node name:	v08k01
Release:	5.8
Version:	Generic_117350-38
Machine:	sun4u
Instance name: proa021
Redo thread mounted by this instance: 1

Process Info
******************
Oracle process number: 117
Unix process pid: 9533, image: oracle@v08k01 (TNS V1-V3)

Error
*********
2009-05-27 13:11:47.847
ksedmp: internal or fatal error
ORA-07445: exception encountered: core dump [memset()+116] [SIGSEGV] [Address not mapped to object] [0] [] []

Current SQL(Current SQL statement for this session)
***********************************************************************
:
SELECT COUNT(PO_LINE_ID) FROM PO_LINES_INTERFACE WHERE PO_HEADER_ID = :b1

Call Stack functions
*************************
ksedmp 

ERROR: ORA-600 [1115]

VERSIONS: versions 6.0 to 10.1

DESCRIPTION: We are encountering a problem while cleaning up a state object.

The State Object is already on free list or has the wrong parent State Object.

FUNCTIONALITY: Kernal Service State object manager

IMPACT:
POSSIBLE INSTANCE FAILURE
PROCESS FAILURE
NON CORRUPTIVE - No underlying data corruption.

SUGGESTIONS: This error may be reported as a direct result of another earlier problem.

Lot of bugs reported

Bug 3837965 : Abstract: ORA-7445'S AND 600'S LEADING UP TO DB CRASH
Comp Version: 8.1.7.4.0
Fixed In Version: 9.2.0.
-------------------------------------------------------------

Bug 3134843 : Abstract: ORACLE PROCESSES CRASHING WITH ORA-7445 SEGVIO ON A NUMBER OF DATABASES
Comp Version: 8.1.7.4
Status: Closed, could not be reproduced
----------------------------------------------------------------

Bug 2760836: Abstract: PMON cleanup of dead shared servers/dispatchers can crash instance(OERI:26599 / OERI 1115)

--------------------------------------------------------------
Note 2760836.8 PMON cleanup of dead shared servers/dispatchers can crash instance (OERI 26599 / OERI 1115)
----------------------------------------------------------------

PROPOSED SOLUTION JUSTIFICATION(S)
==================================
1. One-off patch for Bug 2760836 has fixed this issue...so after customer apply the one-off patch...then this issue will be solved.

OR

2. 9.2.0.4 or later version has fixed this issue...so after customer upgrade to at least 9.2.0.4 version...then this issue will be solved.

The solution can be justified by the followings:

Note 2760836.8 PMON cleanup of dead shared servers/dispatchers can crash instance (OERI 26599 / OERI 1115)