Re: [PATCH 6/6] mm, memcg: Prevent mem_cgroup_protected store tearing

[Michal Hocko]

On Thu 12-03-20 17:33:16, Chris Down wrote:
> The read side of this is all protected, but we can still tear if
> multiple iterations of mem_cgroup_protected are going at the same time.
> 
> There's some intentional racing in mem_cgroup_protected which is ok, but
> load/store tearing should be avoided.
> 
> Signed-off-by: Chris Down <chris@xxxxxxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Roman Gushchin <guro@xxxxxx>
> Cc: Tejun Heo <tj@xxxxxxxxxx>
> Cc: linux-mm@xxxxxxxxx
> Cc: cgroups@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Cc: kernel-team@xxxxxx

Acked-by: Michal Hocko <mhocko@xxxxxxxx>

> ---
>  mm/memcontrol.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 57048a38c75d..e9af606238ab 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -6301,8 +6301,8 @@ enum mem_cgroup_protection mem_cgroup_protected(struct mem_cgroup *root,
>  	}
>  
>  exit:
> -	memcg->memory.emin = emin;
> -	memcg->memory.elow = elow;
> +	WRITE_ONCE(memcg->memory.emin, emin);
> +	WRITE_ONCE(memcg->memory.elow, elow);
>  
>  	if (usage <= emin)
>  		return MEMCG_PROT_MIN;
> -- 
> 2.25.1

-- 
Michal Hocko
SUSE Labs