hm, i just got this nasty looking crash during function-tracer 
self-test:

initcall init_stack_trace+0x0/0x39 returned -1 after 107421 usecs
initcall init_stack_trace+0x0/0x39 returned with error code -1 
calling  init_function_trace+0x0/0x65 @ 1
Testing tracer function: <0>invalid opcode: 0000 [#1] PREEMPT SMP 
last sysfs file: 
CPU 1 
Pid: 589, comm: rcu_torture_wri Not tainted 2.6.29-rc8-tip #21831 System Product Name
RIP: 0010:[<ffffffff8026867e>]  [<ffffffff8026867e>] normalize_rt_tasks+0x12/0x1dd
RSP: 0018:ffff88003ebd3e18  EFLAGS: 00010a87
RAX: ffff88003ebd3eb0 RBX: 0000000000000001 RCX: 0000000056f69185
RDX: 0000000000000000 RSI: ffffffff806b61d2 RDI: ffffffff806b61d2
RBP: ffff88003ebd3e40 R08: 00000000e494e9d2 R09: 00000000e494e9d2
R10: 00000000e494e9d2 R11: 00000000e494e9d2 R12: 000000000017be40
R13: 0000000056f69185 R14: 0000000000000001 R15: ffffffff81893f98
FS:  0000000000000000(0000) GS:ffff880006770000(0000) knlGS:0000000000000000
CS:  0010 DS: 0018 ES: 0018 CR0: 000000008005003b
CR2: 0000000000000000 CR3: 0000000000201000 CR4: 00000000000006a0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process rcu_torture_wri (pid: 589, threadinfo ffff88003ebd2000, task ffff88003eb212f0)
Stack:
 ffffffff8026425d 000000000017be40 0000000056f690e7 0000000000000001
 0000000000000001 ffff88003ebd3e70 ffffffff80267462 ffff88003ebd3e70
 ffffffff8029a761 00000000e494e9d2 0000000056f1925a ffff88003ebd3eb0
Call Trace:
 [<ffffffff8026425d>] ? get_parent_ip+0xe/0x6c
 [<ffffffff80267462>] sub_preempt_count+0xab/0xe1
PASSED
Testing dynamic ftrace: <0> [<ffffffff8029a761>] ? trace_hardirqs_on+0x20/0x36
 [<ffffffff806b62cc>] delay_tsc+0x7d/0x111
 [<ffffffff806b61d2>] __udelay+0x54/0x6a
 [<ffffffff802af445>] rcu_torture_writer+0xf1/0x1c9
 [<ffffffff802af354>] ? rcu_torture_writer+0x0/0x1c9
 [<ffffffff802889f1>] kthread+0x61/0xa4
 [<ffffffff8022d5da>] child_rip+0xa/0x20
 [<ffffffff80267313>] ? finish_task_switch+0xa7/0x14b
 [<ffffffff80e717b7>] ? _spin_unlock_irq+0x50/0x82
 [<ffffffff8022cf54>] ? restore_args+0x0/0x30
 [<ffffffff80288990>] ? kthread+0x0/0xa4
 [<ffffffff8022d5d0>] ? child_rip+0x0/0x20
Code: 65 48 33 14 25 28 00 00 00 74 05 e8 c0 69 00 00 41 59 41 5a 5b 41 5c 5d c3 55 48 89 e5 41 57 41 56 41 55 41 54 53 48 83 ec 28 0f <1f> 44 00 00 65 48 8b 04 25 28 00 00 00 48 89 45 d0 31 c0 48 c7 
RIP  [<ffffffff8026867e>] normalize_rt_tasks+0x12/0x1dd
 RSP <ffff88003ebd3e18>
---[ end trace 5a5d197966b56a2e ]---
Kernel panic - not syncing: Fatal exception
Rebooting in 1 seconds..Press any key to enter the menu

config attached.

normalize_rt_tasks makes absolutely zero sense - it was not 
triggered. I suspect some code patching gotcha ...

	Ingo