linux-kernel - RE: [regression]: soft lockup in dmesg after suspend/resume

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Date:	Wed, 6 Jan 2010 14:12:16 +0800
From:	"Zou, Nanhai" <nanhai.zou@...el.com>
To:	"mingo@...e.hu" <mingo@...e.hu>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	"Zhao, Yakui" <yakui.zhao@...el.com>
Subject: RE: [regression]: soft lockup in dmesg after suspend/resume


>>-----Original Message-----
>>From: Zhao, Yakui
>>Sent: 2010年1月4日 13:37
>>To: mingo@...e.hu
>>Cc: linux-kernel@...r.kernel.org; Zou, Nanhai; Pallipadi, Venkatesh
>>Subject: [regression]: soft lockup in dmesg after suspend/resume
>>
>>Hi,
>>   My box can work well before suspend/resume. But it will complain the
>>following warning message after suspend/resume.
>>   >[1266874868.022103] Enabling non-boot CPUs ...
>>[1266874868.022198] BUG: soft lockup - CPU#0 stuck for 0s! [kthreadd:2]
>>
>>    At the same time after I add the boot option of "printk.time=1", I
>>find that the log time is changed spontaneously from 76 to 1266874868.
>>    > [   76.475266] CPU3 is down
>>[   76.475312] Extended CMOS year: 2000
>>[1266874868.020631] x86 PAT enabled: cpu 0, old 0x7040600070406, new
>>0x7010600070106
>>[1266874868.021779] Back to C!
>>[1266874868.022003] CPU0: Thermal LVT vector (0xfa) already installed
>>[1266874868.022060] Extended CMOS year: 2000
>>
>>    More detailed info can be found in the attached file of
>>dmesg_after_origin.
>>
>>   After I look at the source code, I find that on this box the TSC runs
>>at constant rate with P/T states and does not stop in deep C-states. And
>>then the sched_clock_stable is set to 1. In such case the TSC time is
>>used directly in the function of sched_clock_cpu.
>>
>>   Then I do another test on this box, in which the clock_stable flag is
>>saved/restored in course of suspend/resume(I add this by using per-cpu
>>structure). When entering the suspended state, the clock_stable will be
>>cleared. And when the system is resumed, the clock_stable will be set
>>again. But unfortunately the soft lockup still exists. The file of
>>dmesg_after_test2 is the dmesg log after I save/restore the clock_stable
>>flag in course of suspend/resume.
>>
>>   How about clearing the sched_clock_stable flag even when TSC doesn't
>>stop in deep C-state?  From my test it seems that the TSC value is
>>unknown after doing suspend/resume.
>>
>>Thanks.
>>   Yakui.

Hi Ingo,
	How do you think about this bug? 
This is introduced by the sched_clock_stable flag, 
TSC is stable except when CPU is suspending, we see suspend/resume hang on those machines.
     Maybe we can ignore sched_clock_stable flag when CPU is suspending?

Thanks
Zou Nan hai