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Date: Tue, 23 Nov 2010 15:39:10 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: tip-bot for Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: linux-tip-commits@vger.kernel.org, linux-kernel@vger.kernel.org,
        hpa@zytor.com, mingo@redhat.com, tglx@linutronix.de, mingo@elte.hu
Subject: Re: [tip:sched/core] cpu: Remove incorrect BUG_ON
Message-ID: <20101123143910.GA31502@redhat.com>
References: <tip-51a96c77815e7f139892a6e9c8275a50e9baebdf@git.kernel.org>
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On 11/23, tip-bot for Peter Zijlstra wrote:
>
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -249,8 +249,11 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
>  	 * The migration_call() CPU_DYING callback will have removed all
>  	 * runnable tasks from the cpu, there's only the idle task left now
>  	 * that the migration thread is done doing the stop_machine thing.
> +	 *
> +	 * Wait for the stop thread to go away.
>  	 */
> -	BUG_ON(!idle_cpu(cpu));
> +	while (!idle_cpu(cpu))
> +		cpu_relax();

Yes... but I still can't understand why should we wait at all.

Peter, I am just curious, help ;)

Oleg.