stuck spin lock with many concurrent users

I have seen problems with extremely many concurrent users.
I run pgbench:

pgbench -c 1000 -t 1 test

And I get stuck spin lock errors. This is 100% reproducable (i.e. I
have nerver succeeded in pgbench -c 1000).

This is Linux kernel 2.2.18. Followings are some resource settings
that seem crytical to me.

kernel.shmall = 134217728
kernel.shmmax = 134217728
fs.file-max = 65536

There are 1GB physical memory and 2GB swap space. Note that same
things happen in Sparc/Solaris with much less users (500 concurrent
users).
--
Tatsuo Ishii