linux-kernel - Re: [Next] CPU Hotplug test failures on powerpc

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Date:	Tue, 15 Dec 2009 19:17:28 +0530
From:	Sachin Sant <sachinp@...ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Linux/PPC Development <linuxppc-dev@...abs.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>, linux-next@...r.kernel.org
Subject: Re: [Next] CPU Hotplug test failures on powerpc

Peter Zijlstra wrote:
>> I added some debug statements within the above code. 
>> This is a 2 cpu machine.
>>
>> XMON dest_cpu = 1024 . dead_cpu = 1 . nr_cpu_ids = 2
>> XMON dest_cpu = 1024 
>> XMON dest_cpu = 1024 . dead_cpu = 1
>> XMON dest_cpu = 1024 . dead_cpu = 1 . nr_cpu_ids = 2
>> XMON dest_cpu = 1024 
>> XMON dest_cpu = 1024 . dead_cpu = 1
>> XMON dest_cpu = 1024 . dead_cpu = 1 . nr_cpu_ids = 2
>> XMON dest_cpu = 1024 
>> XMON dest_cpu = 1024 . dead_cpu = 1
>>
>> Seems to me that the control is stuck in an infinite loop and hence the
>> machine appears to be in hung state. The dest_cpu value is always 1024
>> and never changes, which result in an infinite loop.
>>
>> In working scenario the o/p is something on the following lines
>>
>> XMON dest_cpu = 1024 . dead_cpu = 1 . nr_cpu_ids = 2
>> XMON dest_cpu = 0 
>> XMON dest_cpu = 1024 . dead_cpu = 1 . nr_cpu_ids = 2
>> XMON dest_cpu = 0 
>> XMON dest_cpu = 1024 . dead_cpu = 1 . nr_cpu_ids = 2
>> XMON dest_cpu = 0 
>>
>> Let me know if i should try to record any specific value ?
>>     
>
> Could you possibly print the two masks themselves? cpumask_scnprintf()
> and friend come in handy for this.
>
> The dest_cpu=1024 thing seem to suggest the intersection between
> p->cpus_allowed and cpu_active_mask is empty for some reason, even
> though we forcefully reset p->cpus_allowed to the full set using
> cpuset_cpus_allowed_locked().
>   
So here is the data related to the two masks.

cpu_active_mask = 00000000,00000000,00000000,00000000,00000000,00000000,
00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,
00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,
00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,
00000000,00000000
XMON dest_cpu = 1024

while p->cpus_allowed =  00000000,00000000,00000000,00000000,00000000,
00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,
00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,
00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,
00000000,00000000,00000001
XMON dest_cpu = 1024

In working scenario the above data looks like

cpu_active_mask = 00000000,00000000,00000000,00000000,00000000,00000000,
00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,
00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,
00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,
00000000,00000002
XMON dest_cpu = 1

while p->cpus_allowed =  00000000,00000000,00000000,00000000,00000000,
00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,
00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,
00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,
00000000,00000000,00000002
XMON dest_cpu = 1


hope i got the data correct.

Thanks
-Sachin


-- 

---------------------------------
Sachin Sant
IBM Linux Technology Center
India Systems and Technology Labs
Bangalore, India
---------------------------------

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