Hi Paul,

Fortunately this bug is bisectable and the first bad commit is:

        commit 9b2e4f1880b789be1f24f9684f7a54b90310b5c0
        Author: Paul E. McKenney <paul.mckenney@linaro.org>
        Date:   Fri Sep 30 12:10:22 2011 -0700

            rcu: Track idleness independent of idle tasks

However, at that commit, the error messages are a bit different:

[    1.665656] WARNING: at /c/wfg/linux/kernel/rcutiny.c:67 rcu_idle_enter_common+0x103/0x1b2()
[    1.668811] WARNING: at /c/wfg/linux/kernel/rcutiny.c:112 rcu_idle_exit_common+0xfa/0x18c()
[    4.758670] WARNING: at /c/wfg/linux/kernel/trace/trace_events.c:1720 event_trace_self_tests_init+0x87/0x11b()

Here is the first back trace:

[    1.660165] Testing tracer function: 
[    1.664825] ------------[ cut here ]------------
[    1.665656] WARNING: at /c/wfg/linux/kernel/rcutiny.c:67 rcu_idle_enter_common+0x103/0x1b2()
[    1.667006] Hardware name: Bochs
[    1.667583] Modules linked in:
[    1.668106] Pid: 0, comm: swapper Not tainted 3.2.0-rc5+ #41
[    1.668811] Call Trace:
[    1.668811]  [<c13edf12>] ? printk+0x2b/0x3b
[    1.668811]  [<c104b892>] warn_slowpath_common+0xfc/0x13b
[    1.668811]  [<c10f3c2c>] ? rcu_idle_enter_common+0x103/0x1b2
[    1.668811]  [<c10f3c2c>] ? rcu_idle_enter_common+0x103/0x1b2
[    1.668811]  [<c104b90f>] warn_slowpath_null+0x3e/0x4e
[    1.668811]  [<c10f3c2c>] rcu_idle_enter_common+0x103/0x1b2
[    1.668811]  [<c10f3ed3>] rcu_irq_exit+0x1f8/0x20f
[    1.668811]  [<c1058ca4>] irq_exit+0x117/0x14d
[    1.668811]  [<c1005c45>] do_IRQ+0xe5/0x106
[    1.668811]  [<c109e6b8>] ? trace_hardirqs_off_caller+0x97/0x167
[    1.668811]  [<c1408a75>] common_interrupt+0x35/0x3c
[    1.668811]  [<c10a00e0>] ? print_shortest_lock_dependencies+0xec/0x292
[    1.668811]  [<c1023e16>] ? native_safe_halt+0x18/0x28
[    1.668811]  [<c100e10f>] default_idle+0xd7/0x1f0
[    1.668811]  [<c1001eb3>] cpu_idle+0x1c4/0x2c8
[    1.668811]  [<c13e9027>] rest_init+0x1db/0x1ef
[    1.668811]  [<c13e8e4c>] ? reciprocal_value+0x64/0x64
[    1.668811]  [<c16cc232>] start_kernel+0x8e5/0x8f9
[    1.668811]  [<c16cb36b>] ? loglevel+0x55/0x55
[    1.668811]  [<c16cb208>] ? reserve_ebda_region+0xb9/0xc9
[    1.668811]  [<c16cb13a>] i386_start_kernel+0x13a/0x14f

Thanks,
Fengguang