Re: [BUGFIX][PATCH] memcg: fix try_get_mem_cgroup_from_swapcache()

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Mon, 27 Apr 2009 09:51:00 +0900
Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:

> From: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
> 
> memcg: fix try_get_mem_cgroup_from_swapcache()
> 
> This is a bugfix for commit 3c776e64660028236313f0e54f3a9945764422df(included 2.6.30-rc1).
> Used bit of swapcache is solid under page lock, but considering move_account,
> pc->mem_cgroup is not.
> 
> We need lock_page_cgroup() anyway.
> 
> Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>

you are right.
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

> ---
>  mm/memcontrol.c |    5 ++---
>  1 files changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index ccc69b4..84f856c 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1024,9 +1024,7 @@ static struct mem_cgroup *try_get_mem_cgroup_from_swapcache(struct page *page)
>  		return NULL;
>  
>  	pc = lookup_page_cgroup(page);
> -	/*
> -	 * Used bit of swapcache is solid under page lock.
> -	 */
> +	lock_page_cgroup(pc);
>  	if (PageCgroupUsed(pc)) {
>  		mem = pc->mem_cgroup;
>  		if (mem && !css_tryget(&mem->css))
> @@ -1040,6 +1038,7 @@ static struct mem_cgroup *try_get_mem_cgroup_from_swapcache(struct page *page)
>  			mem = NULL;
>  		rcu_read_unlock();
>  	}
> +	unlock_page_cgroup(pc);
>  	return mem;
>  }
>  
> 

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