linux-kernel - Re: tip/master broken with x2apic and kexec

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Date:	Wed, 14 Jul 2010 15:57:48 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	Don Zickus <dzickus@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: tip/master broken with x2apic and kexec

On 07/14/2010 02:23 PM, Yinghai Lu wrote:
> On 07/14/2010 01:35 PM, Yinghai Lu wrote:
>> On 07/13/2010 04:27 PM, Yinghai Lu wrote:
>>> On 07/13/2010 03:00 PM, H. Peter Anvin wrote:
>>>> On 07/12/2010 07:59 PM, Yinghai Lu wrote:
>>>>> tip/master: 
>>>>> system1: BIOS enabled x2apic, first kernel boot well, and when kexec second kernel will cause system instant reboot.
>>>>>
>>>>> system2: BIOS not enable x2apic, first kernel boot well and enable x2apic, and kexec second kernel well. but when kexec third kernel will case system instant reboot.
>>>>>
>>>>> linus' tree is ok.
>>>>>
>>>>> but for system2 if boot with nox2apic ,intr-remaping off, iommu off, the kexec loop test will pass.
>>>>>
>>>>> the problem looks start in recent two or three weeks.
>>>>>
>>>>> Any idea?
>>>>>
>>>>> bisecting will take a while, because the system post take a while everytime.
>>>>>
>>>>> Thanks
>>>>>
>>>>> Yinghai Lu
>>>>
>>>> OK, I found the bug... if you could test out the patch which will be
>>>> sent out shortly I would very much appreciate it.
>>>
>>> not sure if your patch is the offending one now.
>>>
>>> kL: kernel from linus tree
>>> kT1: kernel from tip
>>> kT2: kernel from tip with reverting your patch
>>>
>>> BIOS-->kL ---> kL ---> kL....always working
>>> BIOS-->kT1 ---> kT1 --->  kT1 : between second one and third one system reset instant...
>>> BIOS-->kT2 ---> kT2 --->  kT2 : between second one and third one system reset instant...
>>>
>>> BIOS-->kL ---> kL ---> kL ---> then kT1 ---> kT1 .... always working
>>> BIOS-->kL ---> kL ---> kL ---> then kT2 ---> kT2 .... always working
>>>
>>
>> bisecting said:
>>
>>> git bisect good
>> 58687acba59266735adb8ccd9b5b9aa2c7cd205b is the first bad commit
>> commit 58687acba59266735adb8ccd9b5b9aa2c7cd205b
>> Author: Don Zickus <dzickus@...hat.com>
>> Date:   Fri May 7 17:11:44 2010 -0400
>>
>>     lockup_detector: Combine nmi_watchdog and softlockup detector
>>     
>>     The new nmi_watchdog (which uses the perf event subsystem) is very
>>     similar in structure to the softlockup detector.  Using Ingo's
>>     suggestion, I combined the two functionalities into one file:
>>     kernel/watchdog.c.
>>     
>>     Now both the nmi_watchdog (or hardlockup detector) and softlockup
>>     detector sit on top of the perf event subsystem, which is run every
>>     60 seconds or so to see if there are any lockups.
>>     
>>     To detect hardlockups, cpus not responding to interrupts, I
>>     implemented an hrtimer that runs 5 times for every perf event
>>     overflow event.  If that stops counting on a cpu, then the cpu is
>>     most likely in trouble.
>>     
>>     To detect softlockups, tasks not yielding to the scheduler, I used the
>>     previous kthread idea that now gets kicked every time the hrtimer fires.
>>     If the kthread isn't being scheduled neither is anyone else and the
>>     warning is printed to the console.
>>     
>>     I tested this on x86_64 and both the softlockup and hardlockup paths
>>     work.
>>     
> 
> with
> # CONFIG_LOCKUP_DETECTOR is not set
> # CONFIG_HARDLOCKUP_DETECTOR is not set
> 
> kexec loop test could passed.
> 
> also that patch will break x2apic preenabled system 's kexec/kdump.

before the combining patch

CONFIG_DETECT_SOFTLOCKUP=y
CONFIG_NMI_WATCHDOG=y

will have the same problem.

so the problem should come from NMI_WATCHDOG.

Yinghai


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