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

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Date:	Wed, 14 Jul 2010 19:01:20 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
CC:	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	Don Zickus <dzickus@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: tip/master broken with x2apic and kexec

On 07/14/2010 05:03 PM, Suresh Siddha wrote:
> On Wed, 2010-07-14 at 15:57 -0700, Yinghai Lu wrote:
>> 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, It looks like some timing issue wrt nmi handling/kexec and
> perhaps not directly related to x2apic? Perhaps we should try with
> x2apic disabled but with intr-remapping enabled etc to see if it changes
> anything.

only have "nox2apic", without "nointremap intel_iommu=off"
the kexec loop test work well.

So it is x2apic, nmi_watchdog related...

 Also do we know (like serial console log etc) how far ahead we
> went in the kexec before we rebooted?

will add more printk after "Starting new kernel" to check it.

Thanks

Yinghai
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