linux-kernel - Re: [PATCH] res_counter: fix off-by-one bug in setting limit

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Message-Id: <20080901143007.9c623ef4.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Mon, 1 Sep 2008 14:30:07 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Pavel Emelianov <xemul@...nvz.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] res_counter: fix off-by-one bug in setting limit

On Mon, 01 Sep 2008 13:08:55 +0800
Li Zefan <lizf@...fujitsu.com> wrote:

> I found we can no longer set limit to 0 with 2.6.27-rcX:
>  # mount -t cgroup -omemory xxx /mnt
>  # mkdir /mnt/0
>  # echo 0 > /mnt/0/memory.limit_in_bytes
>  bash: echo: write error: Device or resource busy
> 
> It turned out 'limit' can't be set to 'usage', which is wrong IMO.
> 
> Signed-off-by: Li Zefan <lizf@...fujitsu.com>

But setting limit to 0(usage) in memcg is buggy operation unless you want to see OOM..
Hmm..

Thanks,
-Kame


> ---
>  include/linux/res_counter.h |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/include/linux/res_counter.h b/include/linux/res_counter.h
> index fdeadd9..271c1c2 100644
> --- a/include/linux/res_counter.h
> +++ b/include/linux/res_counter.h
> @@ -166,7 +166,7 @@ static inline int res_counter_set_limit(struct res_counter *cnt,
>  	int ret = -EBUSY;
>  
>  	spin_lock_irqsave(&cnt->lock, flags);
> -	if (cnt->usage < limit) {
> +	if (cnt->usage <= limit) {
>  		cnt->limit = limit;
>  		ret = 0;
>  	}
> -- 1.5.4.rc3 
> 

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