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 for <linuxppc-dev@lists.ozlabs.org>; Sat, 24 Mar 2012 23:44:57 +1100 (EST)
Message-ID: <1332593021.16159.27.camel@twins>
Subject: Re: [PATCH 01/10] cpu: Introduce clear_tasks_mm_cpumask() helper
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Anton Vorontsov <anton.vorontsov@linaro.org>
Date: Sat, 24 Mar 2012 13:43:41 +0100
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References: <20120324102609.GA28356@lizard> <20120324102751.GA29067@lizard>
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Cc: Mike Frysinger <vapier@gentoo.org>,
 user-mode-linux-devel@lists.sourceforge.net, linux-sh@vger.kernel.org,
 Richard Weinberger <richard@nod.at>, linuxppc-dev@lists.ozlabs.org,
 Oleg Nesterov <oleg@redhat.com>, linux-kernel@vger.kernel.org,
 linux-mm@kvack.org, Paul Mundt <lethal@linux-sh.org>,
 John Stultz <john.stultz@linaro.org>,
 KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
 Russell King <linux@arm.linux.org.uk>,
 Andrew Morton <akpm@linux-foundation.org>,
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On Sat, 2012-03-24 at 14:27 +0400, Anton Vorontsov wrote:
> +void clear_tasks_mm_cpumask(int cpu)
> +{
> +       struct task_struct *p;
> +
> +       read_lock(&tasklist_lock);
> +       for_each_process(p) {
> +               struct task_struct *t;
> +
> +               t =3D find_lock_task_mm(p);
> +               if (!t)
> +                       continue;
> +               cpumask_clear_cpu(cpu, mm_cpumask(t->mm));
> +               task_unlock(t);
> +       }
> +       read_unlock(&tasklist_lock);
> +}=20

Why bother with the tasklist_lock at all anymore, afaict you could use
rcu_read_lock() here. This all is called after the cpu is taken down and
marked offline, so its not like new tasks will ever get this cpu set in
their mm mask.