linux-kernel - Re: [PATCH 2/4] stop_machine: reimplement using cpuhog

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Message-ID: <4B9586D3.2020109@kernel.org>
Date:	Tue, 09 Mar 2010 08:22:59 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	linux-kernel@...r.kernel.org, rusty@...tcorp.com.au,
	sivanich@....com, heiko.carstens@...ibm.com,
	torvalds@...ux-foundation.org, mingo@...e.hu, peterz@...radead.org,
	dipankar@...ibm.com, josh@...edesktop.org,
	paulmck@...ux.vnet.ibm.com, akpm@...ux-foundation.org
Subject: Re: [PATCH 2/4] stop_machine: reimplement using cpuhog

Hello,

On 03/09/2010 04:06 AM, Oleg Nesterov wrote:
> On 03/09, Tejun Heo wrote:
>>
>>  int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus)
>>  {
>> ...
>> +	/* Set the initial state and hog all online cpus. */
>> +	set_state(&smdata, STOPMACHINE_PREPARE);
>> +	return hog_cpus(cpu_online_mask, stop_cpu, &smdata);
>>  }
> 
> Could you please confirm this is correct?
> 
> I am not sure I understand how the code looks with the patch applied,
> but the lockless set_state() above can confuse another stop_machine()
> in progress?

set_state() now modifies smdata->state and smdata is now local
variable of __stop_machine().  stop_machine instances don't have any
shared resource anymore.  Synchronization and resource sharing are all
cpuhog's responsibilities.

Thanks.

-- 
tejun
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