Hi Jason,

This warning shows up while doing kernel boot tests in kvm:

[    2.998462] kgdbts: ERROR PUT: end of test buffer on 'do_fork_test' line 2 expected T0* got $W01#b8
[    3.001723] ------------[ cut here ]------------
[    3.003417] WARNING: at /c/kernel-tests/usb/drivers/misc/kgdbts.c:813 run_simple_test+0x39a/0x3c2()
[    3.006654] Modules linked in:
[    3.007855] Pid: 69, comm: reboot Not tainted 3.5.0-rc5+ #23
[    3.009979] Call Trace:
[    3.010919]  [<ffffffff8126302f>] ? run_simple_test+0x39a/0x3c2
[    3.013131]  [<ffffffff8104a7e8>] warn_slowpath_common+0x84/0x9b
[    3.015319]  [<ffffffff8104a819>] warn_slowpath_null+0x1a/0x1c
[    3.017433]  [<ffffffff8126302f>] run_simple_test+0x39a/0x3c2
[    3.019490]  [<ffffffff812626ab>] kgdbts_put_char+0x33/0x35
[    3.021514]  [<ffffffff810c0f40>] gdbstub_exit+0xfb/0x12f
[    3.023474]  [<ffffffff810be2bb>] dbg_notify_reboot+0x46/0x4a
[    3.025560]  [<ffffffff8107e33a>] notifier_call_chain+0x37/0x90
[    3.027695]  [<ffffffff8107e87a>] __blocking_notifier_call_chain+0x62/0x77
[    3.030158]  [<ffffffff8107e8a3>] blocking_notifier_call_chain+0x14/0x16
[    3.032565]  [<ffffffff81067570>] kernel_restart_prepare+0x1d/0x3d
[    3.034785]  [<ffffffff810675a4>] kernel_restart+0x14/0x67
[    3.036799]  [<ffffffff81067795>] sys_reboot+0x18c/0x1ca
[    3.038726]  [<ffffffff8109dd7b>] ? lock_acquire+0xf8/0x12c
[    3.040832]  [<ffffffff81151e09>] ? iterate_supers+0xbc/0x12d
[    3.042906]  [<ffffffff811855b8>] ? __sync_filesystem+0xe4/0xe4
[    3.045163]  [<ffffffff8120baa7>] ? do_raw_spin_unlock+0xee/0x12b
[    3.047410]  [<ffffffff813026f7>] ? sysret_check+0x22/0x5c
[    3.049430]  [<ffffffff8109e1c6>] ? trace_hardirqs_on_caller+0x121/0x17b
[    3.051850]  [<ffffffff81204f5e>] ? trace_hardirqs_on_thunk+0x3a/0x3f
[    3.054189]  [<ffffffff813026cb>] system_call_fastpath+0x1a/0x1f

and the oops is introduced by

2366e047840e33928803c0442176fb3991423da8 is the first bad commit
commit 2366e047840e33928803c0442176fb3991423da8
Author: Jason Wessel <jason.wessel@windriver.com>
Date:   Fri Mar 16 14:20:41 2012 -0500

    kgdb,debug-core,gdbstub: Hook the reboot notifier for debugger detach
    
    The gdbstub and kdb should get detached if the system is rebooting.
    Calling gdbstub_exit() will set the proper debug core state and send a
    message to any debugger that is connected to correctly detach.
    
    An attached debugger will receive the exit code from
    include/linux/reboot.h based on SYS_HALT, SYS_REBOOT, etc...
    
    Reported-by: Jan Kiszka <jan.kiszka@siemens.com>
    Signed-off-by: Jason Wessel <jason.wessel@windriver.com>

:040000 040000 5ccb9b38680fc824087e2d2e458de5e3920d0437 e173fa7aa9a110c033ef0daebb3da1b4b6811ab6 M      kernel
bisect run success

Thanks,
Fengguang