On Thu, Aug 01 2013, Sha Zhengju wrote:
> From: Sha Zhengju <handai.szj@xxxxxxxxxx>
>
> 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
^^ Hocko
> rcu_read_lock_held() because RCU is held if !mem_cgroup_disabled().
>
> Signed-off-by: Sha Zhengju <handai.szj@xxxxxxxxxx>
Reviewed-by: Greg Thelen <gthelen@xxxxxxxxxx>
> ---
> 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;
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