Greetings, 

Here is an aged warning, which is bisected down to

        commit 7d36b26be0f3c6b86e3ab7e1539e42f3a3bc79ca
        Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
        Date:   Tue Jul 26 13:13:44 2011 +0200

            lockdep: Fix trace_hardirqs_on_caller()


[   13.392541] Testing tracer irqsoff: PASSED
[   13.428537] Testing tracer branch: [   20.093074] ------------[ cut here ]------------
[   20.093861] WARNING: at /c/kernel-tests/src/stable/kernel/lockdep.c:3493 check_flags+0x166/0x386()
[   20.093861] Pid: 0, comm: swapper/0 Not tainted 3.6.0-rc1-00102-ga184d4e #7
[   20.093861] Call Trace:

[   20.093861]  [<41064af3>] warn_slowpath_common+0x8e/0xcd
[   20.093861]  [<410f1372>] ? check_flags+0x166/0x386
[   20.093861]  [<41064c6b>] warn_slowpath_null+0x30/0x45
[   20.093861]  [<410f1372>] check_flags+0x166/0x386
[   20.093861]  [<410f7cc5>] lock_acquire+0x5b/0x24a
[   20.093861]  [<4107f7d8>] run_timer_softirq+0x2a6/0x77d
[   20.093861]  [<4107f72f>] ? run_timer_softirq+0x1fd/0x77d
[   20.093861]  [<4107f449>] ? spin_unlock_irqrestore+0x26/0x26
[   20.093861]  [<41075293>] __do_softirq+0x234/0x5d6
[   20.093861]  [<4107505f>] ? local_bh_enable_ip+0x2b/0x2b
[   20.093861]  <IRQ>  [<41075adf>] ? irq_exit+0x9d/0x14b
[   20.093861]  [<4103b1b7>] ? smp_apic_timer_interrupt+0xe1/0xfd
[   20.093861]  [<41a75bc7>] ? apic_timer_interrupt+0x2f/0x34
[   20.093861]  [<41151975>] ? ftrace_likely_update+0x3bb/0x446
[   20.093861]  [<41102e17>] ? arch_local_irq_enable+0x6b/0x80
[   20.093861]  [<41a74287>] ? _raw_spin_unlock_irq+0x80/0xc5
[   20.093861]  [<410babf0>] ? finish_task_switch+0x109/0x1df
[   20.093861]  [<410bab8a>] ? finish_task_switch+0xa3/0x1df
[   20.093861]  [<41a7222b>] ? __schedule+0xb89/0xd51
[   20.093861]  [<4112efbe>] ? rcu_idle_exit+0x1d0/0x26c
[   20.093861]  [<4112efd3>] ? rcu_idle_exit+0x1e5/0x26c
[   20.093861]  [<41a7252f>] ? schedule+0x13c/0x14c
[   20.093861]  [<41014615>] ? cpu_idle+0x1d5/0x1fd
[   20.093861]  [<41a01c3d>] ? rest_init+0x319/0x32c
[   20.093861]  [<4216637a>] ? start_kernel+0x84c/0x85f
[   20.093861]  [<42165322>] ? i386_start_kernel+0xf8/0x10b

Thanks,
Fengguang