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

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Message-ID: <7b6bb4a50912152256j58cdc8f6u7fc0f38c60281dc8@mail.gmail.com>
Date:	Wed, 16 Dec 2009 14:56:01 +0800
From:	Xiaotian Feng <xtfeng@...il.com>
To:	Sachin Sant <sachinp@...ibm.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	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

On Tue, Dec 15, 2009 at 9:47 PM, Sachin Sant <sachinp@...ibm.com> wrote:
> 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
>

How about cpu_online_mask? commit 6ad4c1 switches from cpu_online_mask
to cpu_active_mask.
Is there a mismatch for cpu_online_mask and cpu_active_mask?

> 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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