Re: [PATCH] memcg: fix kmemcg registration for late caches

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

(2013/02/12 1:39), Glauber Costa wrote:
> The designed workflow for the caches in kmemcg is: register it with
> memcg_register_cache() if kmemcg is already available or later on when a
> new kmemcg appears at memcg_update_cache_sizes() which will handle all
> caches in the system. The caches created at boot time will be handled by
> the later, and the memcg-caches as well as any system caches that are
> registered later on by the former.
> 
> There is a bug, however, in memcg_register_cache: we correctly set up
> the array size, but do not mark the cache as a root cache. This means
> that allocations for any cache appearing late in the game will see
> memcg->memcg_params->is_root_cache == false, and in particular, trigger
> VM_BUG_ON(!cachep->memcg_params->is_root_cache) in
> __memcg_kmem_cache_get.
> 
> The obvious fix is to include the missing assignment.
> 
> Signed-off-by: Glauber Costa <glommer@parallels.com>

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

> ---
>   mm/memcontrol.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 03ebf68..d4e83d0 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3147,7 +3147,9 @@ int memcg_register_cache(struct mem_cgroup *memcg, struct kmem_cache *s,
>   	if (memcg) {
>   		s->memcg_params->memcg = memcg;
>   		s->memcg_params->root_cache = root_cache;
> -	}
> +	} else
> +		s->memcg_params->is_root_cache = true;
> +
>   	return 0;
>   }
>   
> 


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