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Date:	Sat, 05 Apr 2014 12:30:12 +0800
From:	Jet Chen <jet.chen@...el.com>
To:	Viresh Kumar <viresh.kumar@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>
CC:	Fengguang Wu <fengguang.wu@...el.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: WARNING: CPU: 0 PID: 1935 at kernel/timer.c:1621 migrate_timer_list()

On 04/04/2014 03:52 PM, Viresh Kumar wrote:
> On 4 April 2014 13:16, Jet Chen <jet.chen@...el.com> wrote:
>> Hi Viresh,
>>
>> I changed your print message as you suggested.
>>
>> diff --git a/kernel/timer.c b/kernel/timer.c
>> index 6c3a371..193101d 100644
>> --- a/kernel/timer.c
>> +++ b/kernel/timer.c
>> @@ -1617,8 +1617,8 @@ static void migrate_timer_list(struct tvec_base
>> *new_base, struct list_head *hea
>>
>>                   /* Check if CPU still has pinned timers */
>>                   if (unlikely(WARN(is_pinned,
>> -                                 "%s: can't migrate pinned timer: %p,
>> deactivating it\n",
>> -                                 __func__, timer)))
>> +                                 "%s: can't migrate pinned timer: %p,
>> timer->function: %p,deactivating it\n",
>> +                                 __func__, timer, timer->function)))
>>                           continue;
>>
>> Then I reproduced the issue, and got the dmesg output,
>>
>> [   37.918406] migrate_timer_list: can't migrate pinned timer:
>> ffffffff81f06a60, timer->function: ffffffff810d7010,deactivating it
>>
>> We reproduced this issue for several times in our LKP system. The address of
>> timer ffffffff81f06a60 is very constant. So is timer->function, I believe.
>>
>> Hope this information will help you. Please feel free to tell me what else I
>> can do to help you.
>
> Hi Jet,
>
> Thanks a lot. Yes that's pretty helpful.. But I need some more help from you..
> I don't have any idea which function has this address in your kernel:
> ffffffff810d7010 :)
>
> Can you please debug that a bit more? You need to find which function
> this address belongs to. You can try that using objdump on your vmlinux.
>
> Some help can be found here: Documentation/BUG-HUNTING
>
> Thanks in Advance.
>
vmlinuz from our build system doesn't have debug information. It is hard 
to use objdump to identify which routine is timer->function.
But after several times trials, I get below dmesg messages.
It is clear to see address of "timer->function" is 0xffffffff810d7010.
In calling stack, " [<ffffffff810d7010>] ? 
clocksource_watchdog_kthread+0x40/0x40 ". So I guess timer->function is 
clocksource_watchdog_kthread.
I manually disable CONFIG_CLOCKSOURCE_WATCHDOG, then I never see this 
oops again (But see other oops for other reason :( )


[   37.918345] WARNING: CPU: 0 PID: 1932 at kernel/timer.c:1621 
migrate_timer_list+0xdb/0xf0()
[   37.918406] migrate_timer_list: can't migrate pinned timer: 
ffffffff81f06a60, timer->function: ffffffff810d7010,deactivating it
[   37.918406] Modules linked in:
[   37.918406] CPU: 0 PID: 1932 Comm: 01-cpu-hotplug Not tainted 
3.14.0-rc1-00088-gab3c4fd #4
[   37.918406] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[   37.918406]  0000000000000009 ffff88001d407c38 ffffffff817237bd 
ffff88001d407c80
[   37.918406]  ffff88001d407c70 ffffffff8106a1dd 0000000000000010 
ffffffff81f06a60
[   37.918406]  ffff88001e04d040 ffffffff81e3d4c0 ffff88001e04d030 
ffff88001d407cd0
[   37.918406] Call Trace:
[   37.918406]  [<ffffffff817237bd>] dump_stack+0x4d/0x66
[   37.918406]  [<ffffffff8106a1dd>] warn_slowpath_common+0x7d/0xa0
[   37.918406]  [<ffffffff8106a24c>] warn_slowpath_fmt+0x4c/0x50
[   37.918406]  [<ffffffff810761c3>] ? __internal_add_timer+0x113/0x130
[   37.918406]  [<ffffffff810d7010>] ? 
clocksource_watchdog_kthread+0x40/0x40
[   37.918406]  [<ffffffff8107753b>] migrate_timer_list+0xdb/0xf0
[   37.918406]  [<ffffffff810782dc>] timer_cpu_notify+0xfc/0x1f0
[   37.918406]  [<ffffffff8173046c>] notifier_call_chain+0x4c/0x70
[   37.918406]  [<ffffffff8109340e>] __raw_notifier_call_chain+0xe/0x10
[   37.918406]  [<ffffffff8106a3f3>] cpu_notify+0x23/0x50
[   37.918406]  [<ffffffff8106a44e>] cpu_notify_nofail+0xe/0x20
[   37.918406]  [<ffffffff81712a5d>] _cpu_down+0x1ad/0x2e0
[   37.918406]  [<ffffffff81712bc4>] cpu_down+0x34/0x50
[   37.918406]  [<ffffffff813fec54>] cpu_subsys_offline+0x14/0x20
[   37.918406]  [<ffffffff813f9f65>] device_offline+0x95/0xc0
[   37.918406]  [<ffffffff813fa060>] online_store+0x40/0x90
[   37.918406]  [<ffffffff813f75d8>] dev_attr_store+0x18/0x30
[   37.918406]  [<ffffffff8123309d>] sysfs_kf_write+0x3d/0x50



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