linux-kernel - Re: [PATCH 1/3] memcg: oom wakeup filter

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Date:	Mon, 15 Mar 2010 14:50:13 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
	"kirill@...temov.name" <kirill@...temov.name>
Subject: Re: [PATCH 1/3] memcg: oom wakeup filter

On Fri, 12 Mar 2010 14:31:37 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:

> +static int memcg_oom_wake_function(wait_queue_t *wait,
> +	unsigned mode, int sync, void *arg)
> +{
> +	struct mem_cgroup *wake_mem = (struct mem_cgroup *)arg;
> +	struct oom_wait_info *oom_wait_info;
> +
> +	/* both of oom_wait_info->mem and wake_mem are stable under us */
> +	oom_wait_info = container_of(wait, struct oom_wait_info, wait);
> +
> +	if (oom_wait_info->mem == wake_mem)
> +		goto wakeup;
> +	/* if no hierarchy, no match */
> +	if (!oom_wait_info->mem->use_hierarchy || !wake_mem->use_hierarchy)
> +		return 0;
> +	/* check hierarchy */
> +	if (!css_is_ancestor(&oom_wait_info->mem->css, &wake_mem->css) &&
> +	    !css_is_ancestor(&wake_mem->css, &oom_wait_info->mem->css))
> +		return 0;
> +
> +wakeup:
> +	return autoremove_wake_function(wait, mode, sync, arg);
> +}

What are the locking rules for calling css_is_ancestor()?
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