RHEL5.3 6u14 64-bit rare hang in Runtime.exec to glibc fork

RHEL5.3 Java 6u14 64-bit hang in fork

Some java programs which invoke linux commands intermittently hang up.
In the native stack trace, libc fork is blocked by an IO lock before calling the real
fork system call.

Thread 108 (process 12287):
#0 0x00000032ee0dee6e in __lll_lock_wait_private () from /lib64/libc.so.6
#1 0x00000032ee06ebe1 in _L_lock_2271 () from /lib64/libc.so.6
#2 0x00000032ee06dfdf in __GI__IO_list_lock () from /lib64/libc.so.6
#3 0x00000032ee09980f in fork () from /lib64/libc.so.6
#4 0x00002aaaaabe5eee in Java_java_lang_UNIXProcess_forkAndExec ()
   from /usr/local/jdk1.6.0_14/jre/lib/amd64/libjava.so
#5 0x00002aaaab146ece in ?? ()
#6 0x0000000000000000 in ?? ()

This thread is waiting for the IO lock to be unlocked and its wakeup from kernel,
which does not happen when the symptom was seen.

Out of around 1000 servers,about 10 incidents of this symptom were reported for RHEL 5.3 + 6u14~6u19 64-bit.