On Tue, Jul 10, 2012 at 10:58:35AM +0800, wfg@linux.intel.com wrote:
> Hi Jason,
> 
> This HEAD commit in kgdb-next makes kgdb boot time tests freeze.
> The kernel is tested inside kvm with the attached config.
> 
> 3751d3e85cf693e10e2c47c03c8caa65e171099b is the first bad commit
> commit 3751d3e85cf693e10e2c47c03c8caa65e171099b
> Author: Jason Wessel <jason.wessel@windriver.com>
> Date:   Fri Mar 23 09:35:05 2012 -0500
> 
>     x86,kgdb: Fix DEBUG_RODATA limitation using text_poke()

Jason, now that commit is merged into Linus' tree and showing up in
various other development trees that base on v3.6-rc1.

kernel boots reliably freeze on:
[    4.527958] Write protecting the kernel read-only data: 10240k
[    4.529326] debug: unmapping init memory ffff880001522000..ffff880001600000
[    4.530566] debug: unmapping init memory ffff880001829000..ffff880001a00000
[    4.549375] KGDB: BP remove failed: ffffffff81035be9

The freeze will disappear if removing CONFIG_KGDB*. It will change
into this oops if reverting the commit (either doing it on v3.6-rc1,
or by checking out 3751d3e85c~1):

[    3.027423] kgdbts: ERROR PUT: end of test buffer on 'do_fork_test' line 2 expected T0* got $W01#b8
[    3.029281] ------------[ cut here ]------------
[    3.030154] WARNING: at /c/wfg/linux/drivers/misc/kgdbts.c:813 run_simple_test+0x24f/0x277()
[    3.031624] Pid: 117, comm: reboot Not tainted 3.6.0-rc1-bisect-00198-gb1b7253 #47
[    3.033271] Call Trace:
[    3.033694]  [<ffffffff813f1a11>] ? run_simple_test+0x24f/0x277
[    3.034881]  [<ffffffff810353f6>] warn_slowpath_common+0x5d/0x74
[    3.036026]  [<ffffffff810354bb>] warn_slowpath_null+0x15/0x1a
[    3.037285]  [<ffffffff813f1a11>] run_simple_test+0x24f/0x277
[    3.038436]  [<ffffffff813f142c>] kgdbts_put_char+0x18/0x1a
[    3.039463]  [<ffffffff81085f88>] gdbstub_exit+0xc6/0xe2
[    3.040568]  [<ffffffff81084cef>] dbg_notify_reboot+0x2a/0x2e
[    3.041632]  [<ffffffff81052568>] notifier_call_chain+0x32/0x5c
[    3.042760]  [<ffffffff810527ff>] __blocking_notifier_call_chain+0x47/0x60
[    3.044054]  [<ffffffff81052827>] blocking_notifier_call_chain+0xf/0x11
[    3.045390]  [<ffffffff810449ae>] kernel_restart_prepare+0x18/0x38
[    3.046511]  [<ffffffff81044a07>] kernel_restart+0xf/0x4b
[    3.047540]  [<ffffffff81044c2f>] sys_reboot+0x129/0x15e
[    3.048732]  [<ffffffff81072f0f>] ? trace_hardirqs_off+0xd/0xf
[    3.049784]  [<ffffffff8105c556>] ? local_clock+0x65/0x8b
[    3.050786]  [<ffffffff8106f8b2>] ? lock_release_holdtime+0x9e/0xa3
[    3.051964]  [<ffffffff81344974>] ? do_raw_spin_unlock+0xa7/0xb0
[    3.053177]  [<ffffffff8155fda5>] ? sysret_check+0x22/0x5d
[    3.054124]  [<ffffffff81072dfc>] ? trace_hardirqs_on_caller+0x125/0x181
[    3.055388]  [<ffffffff81332e8e>] ? trace_hardirqs_on_thunk+0x3a/0x3f
[    3.056667]  [<ffffffff8155fd79>] system_call_fastpath+0x16/0x1b

Attached is the full dmesg for the above oops and config.

Thanks,
Fengguang