linux-kernel - Re: [RFC PATCH 1/4] Refcount Based Cpu-Hotplug Implementation

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Message-Id: <200710171047.42693.rusty@rustcorp.com.au>
Date:	Wed, 17 Oct 2007 10:47:41 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	ego@...ibm.com
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Oleg Nesterov <oleg@...sign.ru>, Ingo Molnar <mingo@...e.hu>,
	Paul E McKenney <paulmck@...ibm.com>
Subject: Re: [RFC PATCH 1/4] Refcount Based Cpu-Hotplug Implementation

On Tuesday 16 October 2007 20:34:17 Gautham R Shenoy wrote:
> This patch implements a Refcount + Waitqueue based model for
> cpu-hotplug.

Hi Gautham,

	I can't see where you re-initialize the completion.  

> +static void cpu_hotplug_begin(void)
> +{
> +	mutex_lock(&cpu_hotplug.lock);
> +	cpu_hotplug.active_writer = current;
> +	while (cpu_hotplug.refcount) {
> +		mutex_unlock(&cpu_hotplug.lock);
> +		wait_for_completion(&cpu_hotplug.readers_done);
> +		mutex_lock(&cpu_hotplug.lock);
> +	}

AFAICT this will busy-wait on the second CPU hotplug.

Cheers,
Rusty.
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