linux-kernel - Re: [PATCH 1/4] cpu_stop: implement stop

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Message-ID: <4BDFC06B.4020805@kernel.org>
Date:	Tue, 04 May 2010 08:36:27 +0200
From:	Tejun Heo <tj@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	mingo@...e.hu, linux-kernel@...r.kernel.org, x86@...nel.org,
	oleg@...hat.com, rusty@...tcorp.com.au, sivanich@....com,
	heiko.carstens@...ibm.com, dipankar@...ibm.com,
	josh@...edesktop.org, paulmck@...ux.vnet.ibm.com,
	akpm@...ux-foundation.org, arjan@...ux.intel.com,
	torvalds@...ux-foundation.org
Subject: Re: [PATCH 1/4] cpu_stop: implement stop_cpu[s]()

Hello,

On 05/03/2010 03:26 PM, Peter Zijlstra wrote:
> On Thu, 2010-04-22 at 18:09 +0200, Tejun Heo wrote:
>> +static int cpu_stopper_thread(void *data)
>> +{
>> +       struct cpu_stopper *stopper = data; 
> 
> BUG_ON(stopper != __get_cpu_var(cpu_stopper)); ?

Added.

>> +       work = NULL;
>> +       spin_lock_irq(&stopper->lock);
>> +       if (!list_empty(&stopper->works)) {
>> +               work = list_first_entry(&stopper->works,
>> +                                       struct cpu_stop_work, list);
>> +               list_del_init(&work->list);
>> +       }
>> +       spin_unlock_irq(&stopper->lock);
> 
> Not sure if its worth the hassle, but you could list_splice_init() the
> complete pending list onto a local list, possible avoiding some locks.
> 
> But since this isn't supposed to be used much, I doubt we'll ever see
> the difference.

Yeah, I think it would be better to keep the code simple there.

>> +               /* restore preemption and check it's still balanced */
>> +               preempt_enable();
>> +               WARN_ON_ONCE(preempt_count());
> 
> You would use WARN_ONCE() and print the function that last ran and
> leaked the preempt count.

Updated to use WARN_ONCE() w/ print the function symbol and argument.

Thanks.

-- 
tejun
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