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

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Message-ID: <1272893189.5605.119.camel@twins>
Date:	Mon, 03 May 2010 15:26:29 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Tejun Heo <tj@...nel.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]()

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)); ?

> +       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.

> +               /* 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.


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