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SubjectRe: [Need Help] Cpuhotplug operations on 32-bit mode of xeon-64bit processor crashes the system.
Siddha, Suresh B wrote:
> Sorry for my delayed response. I was away on vacation.
>
> What platform is this? what do you mean by crashing? Do you see a
> system freeze or oops?
>
Its xeon-64 bit processor,running in 32-bit compatibility
mode(i386-code). We have not seen this problem in x86_64 envioronment.
It happens in 32-bit compatibility mode.

Problem is in calculation of apicid's and delivery of IPI's.

I saw a oops,when I do cpuhotplug operations on it.

If you want any further information,please free to ask.

Thanks
Srinivasa Ds

> thanks,
> suresh
>
> On Mon, Jan 22, 2007 at 01:42:48PM +0530, Srinivasa Ds wrote:
>
>> I saw cpuhotplug operations on 32-bit mode of xeon-64bit processors
>> crashing the system. This happens on latest 2.6.20-rc5 kernel also. Same
>> (i386 cpuhotplug code) runs fine on xeon-32bit processors.
>> Steps to reproduce.
>> ====================
>> echo 0 > /sys/devices/system/cpu/cpu6/online
>> echo 1 > /sys/devices/system/cpu/cpu6/online
>> ================================
>> dmesg shows.
>> ==============
>> Breaking affinity for irq 4
>> cpu_mask_to_apicid: Not a valid mask!
>> CPU 6 is now offline
>> =======================
>>
>> On debugging the problem, I found that problem is not in cpuhotplug code
>> but in apic part. Execution of "stale" IPI's by onlined cpus(which we
>> offlined earlier) is causing the crash. Now we need to debug,why IPI's
>> are reaching the offlined cpu's too.
>>
>> 1) During the calculation of apicid's, if cpu to which IPI has to
>> deliver is not in
>> same apic cluster,it prints "Not a valid mask" error and returns "0xFF"
>> which means broadcast the IPI's to all cpus(which are offlined too) and
>> hence the problem.
>>
>> 2) I booted the system with maxcpus=2 boot parameter, and tried cpu
>> hotplugging on it.
>> but still problem recreates(I think there is no concept of apic clusters
>> if there are only 2 cpus). Hence it makes me to conclude that problem is
>> in delivery of IPI's.
>>
>> So Iam completely stuck here. Iam not able to move forward in debugging.
>> So could someone(may be intel folks) please throw some light on this.
>>
>> Thanks in advance
>> Srinivasa DS
>> LTC-IBM
>>

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