Re: [PATCH V5 3/8] memcg: check for proper lock held in mem_cgroup_update_page_stat

[Michal Hocko <mhocko@suse.cz>]

On Thu 01-08-13 19:52:26, Sha Zhengju wrote:
> From: Sha Zhengju <handai.szj@taobao.com>
> 
> We should call mem_cgroup_begin_update_page_stat() before
> mem_cgroup_update_page_stat() to get proper locks, however the
> latter doesn't do any checking that we use proper locking, which
> would be hard. Suggested by Michal Hock we could at least test for
> rcu_read_lock_held() because RCU is held if !mem_cgroup_disabled().
> 
> Signed-off-by: Sha Zhengju <handai.szj@taobao.com>

Acked-by: Michal Hocko <mhocko@suse.cz>

> ---
>  mm/memcontrol.c |    1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 7691cef..4a55d46 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2301,6 +2301,7 @@ void mem_cgroup_update_page_stat(struct page *page,
>  	if (mem_cgroup_disabled())
>  		return;
>  
> +	VM_BUG_ON(!rcu_read_lock_held());
>  	memcg = pc->mem_cgroup;
>  	if (unlikely(!memcg || !PageCgroupUsed(pc)))
>  		return;
> -- 
> 1.7.9.5
> 
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-- 
Michal Hocko
SUSE Labs

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