I've had the same problem in a installation with RHEL 5, kernel 2.6.18-8.el5, samba 3.0.28 and openldap-2.3.27-5
We have had random oops when heavy workloads occurs. In one of this lockups we saw in /var/log/messages logs like:
BUG: soft lockup detected on CPU#1!
[<c0140977>] softlockup_tick+0x9a/0xbc
[<c012575a>] update_process_times+0x56/0x79
[<c010f97e>] smp_apic_timer_interrupt+0x5c/0x62
[<c0104277>] apic_timer_interrupt+0x1f/0x24
[<c022122a>] _raw_spin_lock+0x59/0x7d
[<c01f579e>] key_alloc+0x192/0x34a
[<c01f63b8>] keyring_alloc+0x30/0x72
[<c01f7c48>] alloc_uid_keyring+0x48/0xab
[<c0150daf>] __handle_mm_fault+0x1d6/0x255
[<c0125eac>] alloc_uid+0xc6/0x150
[<c0129874>] set_user+0xb/0x90
[<c0129c65>] sys_setresuid+0x9e/0x1ed
[<c0103741>] sysenter_past_esp+0x56/0x79
After googling a lot we did find this:
http://lkml.indiana.edu/hypermail/li...02.1/0546.html