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

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Message-ID: <20070130163049.D32010@unix-os.sc.intel.com>
Date:	Tue, 30 Jan 2007 16:30:49 -0800
From:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>
To:	Srinivasa Ds <srinivasa@...ibm.com>
Cc:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>, ashok.raj@...el,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	mingo@...hat.com
Subject: Re: [Need Help] Cpuhotplug operations on 32-bit mode of xeon-64bit processor crashes the system.

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?

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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