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Date: Thu, 03 Dec 2009 10:15:17 +0800
From: Li Zefan <lizf@cn.fujitsu.com>
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To: Wu Fengguang <fengguang.wu@intel.com>
CC: Andi Kleen <andi@firstfloor.org>,
       Andrew Morton <akpm@linux-foundation.org>,
       KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
       Hugh Dickins <hugh.dickins@tiscali.co.uk>,
       Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>,
       Balbir Singh <balbir@linux.vnet.ibm.com>,
       KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
       Paul Menage <menage@google.com>, Nick Piggin <npiggin@suse.de>,
       "linux-mm@kvack.org" <linux-mm@kvack.org>,
       LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 22/24] HWPOISON: add memory cgroup filter
References: <20091202031231.735876003@intel.com> <20091202043046.519053333@intel.com> <20091202124446.GA18989@one.firstfloor.org> <20091202125842.GA13277@localhost>
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> +#ifdef	CONFIG_CGROUP_MEM_RES_CTLR_SWAP
> +u32 hwpoison_filter_memcg;
> +static int hwpoison_filter_task(struct page *p)
> +{
> +	struct mem_cgroup *mem;
> +	struct cgroup_subsys_state *css;
> +
> +	if (!hwpoison_filter_memcg)
> +		return 0;
> +
> +	mem = try_get_mem_cgroup_from_page(p);
> +	if (!mem)
> +		return -EINVAL;
> +
> +	css = mem_cgroup_css(mem);
> +	if (!css)
> +		return -EINVAL;
> +

Here, if mem != NULL, then css won't be NULL.

> +	css_put(css);
> +	return 0;
> +}