Re: tip/master broken with x2apic and kexec

[Yinghai Lu <yinghai@kernel.org>]

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@redhat.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.

Yinghai