linux-kernel - Re: [mm PATCH 4/6] RCU: preemptible RCU

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Message-Id: <20070123163826.d4ba703a.akpm@osdl.org>
Date:	Tue, 23 Jan 2007 16:38:26 -0800
From:	Andrew Morton <akpm@...l.org>
To:	dipankar@...ibm.com
Cc:	Ingo Molnar <mingo@...e.hu>,
	Paul E McKenney <paulmck@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [mm PATCH 4/6] RCU: preemptible RCU

On Tue, 16 Jan 2007 00:58:58 +0530
Dipankar Sarma <dipankar@...ibm.com> wrote:

> +/*
> + * Wait for CPUs to acknowledge the flip.
> + */
> +static int rcu_try_flip_waitack(int flipctr)
> +{
> +	int cpu;
> +
> +	for_each_possible_cpu(cpu)
> +		if (per_cpu(rcu_flip_flag, cpu) != RCU_FLIP_SEEN) 
> +			return 1;
> +
> +	/*
> +	 * Make sure our checks above don't bleed into subsequent
> +	 * waiting for the sum of the counters to reach zero.
> +	 */
> +	smp_mb();
> +	return 0;
> +}

Confused.  If some of the possible cpus aren't online, doesn't the 
state machine get stuck??
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