Paul,

This should be easier to reproduce. It still does not always happen,
but did happen in many test boxes.

/bin/sh: /proc/self/fd/9: No such file or directory
[   13.889219] ------------[ cut here ]------------
[   13.889945] WARNING: at /c/kernel-tests/src/tip/kernel/lockdep.c:3493 check_flags+0x131/0x320()
[   13.891200] Pid: 8, comm: rcu_kthread Not tainted 3.6.0-rc1-00002-g0c8f7ca #617
[   13.892531] Call Trace:
[   13.893008]  [<ffffffff8112de21>] ? check_flags+0x131/0x320
[   13.894050]  [<ffffffff8109c78d>] warn_slowpath_common+0xad/0xf0
[   13.895166]  [<ffffffff8109c8f5>] warn_slowpath_null+0x25/0x30
[   13.896241]  [<ffffffff8112de21>] check_flags+0x131/0x320
[   13.897266]  [<ffffffff8112fd10>] lock_is_held+0x70/0x140
[   13.898327]  [<ffffffff8110eb9b>] __might_sleep+0x5b/0x3a0
[   13.899165]  [<ffffffff8180ded7>] rt_mutex_lock+0x27/0x50
[   13.899165]  [<ffffffff811573f4>] rcu_boost+0x144/0x270
[   13.899165]  [<ffffffff810f03ad>] ? finish_wait+0x8d/0xd0
[   13.899165]  [<ffffffff8180ee37>] ? _raw_spin_unlock_irqrestore+0x107/0x150
[   13.899165]  [<ffffffff810f03ad>] ? finish_wait+0x8d/0xd0
[   13.899165]  [<ffffffff8115791d>] rcu_kthread+0x15d/0x2c0
[   13.899165]  [<ffffffff810f0510>] ? abort_exclusive_wait+0x120/0x120
[   13.899165]  [<ffffffff811577c0>] ? __rcu_process_callbacks+0x2a0/0x2a0
[   13.899165]  [<ffffffff811577c0>] ? __rcu_process_callbacks+0x2a0/0x2a0
[   13.899165]  [<ffffffff810ee89f>] kthread+0xef/0x100
[   13.899165]  [<ffffffff81812004>] kernel_thread_helper+0x4/0x10
[   13.899165]  [<ffffffff81810870>] ? retint_restore_args+0x13/0x13
[   13.899165]  [<ffffffff810ee7b0>] ? insert_kthread_work+0x1a0/0x1a0
[   13.899165]  [<ffffffff81812000>] ? gs_change+0x13/0x13

Thanks,
Fengguang