linux-kernel - Re: [patch] cpufreq: mark cpufreq_tsc() as core_initcall

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Date:	Mon, 27 Nov 2006 19:56:49 +0300
From:	Oleg Nesterov <oleg@...sign.ru>
To:	"Paul E. McKenney" <paulmck@...ibm.com>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Jens Axboe <jens.axboe@...cle.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [patch] cpufreq: mark cpufreq_tsc() as core_initcall_sync

On 11/27, Oleg Nesterov wrote:
>
> so synchronize_xxx() should be
> 
> 	void synchronize_xxx(struct xxx_struct *sp)
> 	{
> 		int idx;
> 
> 		smp_mb();
> 		mutex_lock(&sp->mutex);
> 
> 		idx = sp->completed & 0x1;
> 		if (atomic_read(sp->ctr + idx) == 1)
> 			goto out;
> 
> 		atomic_inc(sp->ctr + (idx ^ 0x1));
> 		sp->completed++;
> 
> 		atomic_dec(sp->ctr + idx);
> 		wait_event(sp->wq, !atomic_read(sp->ctr + idx));
> 	out:
> 		mutex_unlock(&sp->mutex);
> 	}
> 
> Yes, Alan was right, spinlock_t makes the code simpler.

Damn, it needs another mb() at the end,

	void synchronize_xxx(struct xxx_struct *sp)
	{
		int idx;

		smp_mb();
		mutex_lock(&sp->mutex);

		idx = sp->completed & 0x1;
		if (atomic_read(sp->ctr + idx) == 1)
			goto out;

		atomic_inc(sp->ctr + (idx ^ 0x1));
		sp->completed++;

		atomic_dec(sp->ctr + idx);
		wait_event(sp->wq, !atomic_read(sp->ctr + idx));
	out:
		mutex_unlock(&sp->mutex);
		smp_mb();
	}

Oleg.

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