Tested 6u25 b04 on Oracle Linux 6 x64.
# uname -a
Linux localhost.localdomain 2.6.32-100.28.5.el6.x86_64 #1 SMP Wed Feb 2 18:40:23 EST 2011 x86_64 x86_64 x86_64 GNU/Linux
# cat /etc/*release
Oracle Linux Server release 6.0
Red Hat Enterprise Linux Server release 6.0 (Santiago)
Oracle Linux Server release 6.0
# java -versoin
java version "1.6.0_25"
Java(TM) SE Runtime Environment (build 1.6.0_25-b04)
Java HotSpot(TM) 64-Bit Server VM (build 20.0-b11, mixed mode)

Steps to reproduce;
Can be reproduced by Font2DTest or SwingSet2.

cd $JAVA_HOME/demo/jfc/Font2DTest
AWT_TOOLKIT=MToolkit java -jar Font2DTest.jar
#
# A fatal error has been detected by the Java Runtime Environment:
#
#  SIGSEGV (0xb) at pc=0x000000365d831068, pid=2901, tid=139873253811984
#
# JRE version: 6.0_25-b04
# Java VM: Java HotSpot(TM) 64-Bit Server VM (20.0-b11 mixed mode linux-amd64 compressed oops)
# Problematic frame:
# C  [libc.so.6+0x31068]  char+0x18
#
:
:

Log is attached [hs_err_pid2901.log].