Re: [Need Help] Cpuhotplug operations on 32-bit mode of xeon-64bit processor crashes the system.

[Srinivasa DS <srinivasa@in.ibm.com>]

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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