linux-kernel - Re: [PATCH 2/5] softlockup: make detector be aware of task switch of processes hogging cpu

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Date:	Tue, 19 Aug 2014 09:36:05 +0800
From:	Chai Wen <chaiw.fnst@...fujitsu.com>
To:	Don Zickus <dzickus@...hat.com>
CC:	Ingo Molnar <mingo@...nel.org>, <akpm@...ux-foundation.org>,
	<kvm@...r.kernel.org>, <pbonzini@...hat.com>, <mingo@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/5] softlockup: make detector be aware of task switch
 of processes hogging cpu

On 08/19/2014 04:38 AM, Don Zickus wrote:

> On Mon, Aug 18, 2014 at 09:02:00PM +0200, Ingo Molnar wrote:
>>
>> * Don Zickus <dzickus@...hat.com> wrote:
>>
>>>>>> So I agree with the motivation of this improvement, but 
>>>>>> is this implementation namespace-safe?
>>>>>
>>>>> What namespace are you worried about colliding with?  I 
>>>>> thought softlockup_ would provide the safety??  Maybe I 
>>>>> am missing something obvious. :-(
>>>>
>>>> I meant PID namespaces - a PID in itself isn't guaranteed 
>>>> to be unique across the system.
>>>
>>> Ah, I don't think we thought about that.  Is there a better 
>>> way to do this?  Is there a domain id or something that can 
>>> be OR'd with the pid?
>>
>> What is always unique is the task pointer itself. We use pids 
>> when we interface with user-space - but we don't really do that 
>> here, right?
> 
> No, I don't believe so.  Ok, so saving 'current' and comparing that should
> be enough, correct?
> 


I am not sure of the safety about using pid here with namespace.
But as to the pointer of process, is there a chance that we got a 'historical'
address saved in the 'softlockup_warn_pid(or address)_saved' and the current
hogging process happened to get the same task pointer address?
If it never happens, I think the comparing of address is ok.

thanks
chai wen

> Cheers,
> Don
> .
> 



-- 
Regards

Chai Wen
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