Re: [BUGFIX][PATCH mmotm] memcg: fix for hierarchical reclaim

[Balbir Singh <balbir@linux.vnet.ibm.com>]

Daisuke Nishimura wrote:
> mem_cgroup_from_res_counter should handle both mem->res and mem->memsw.
> This bug leads to NULL pointer dereference BUG at mem_cgroup_calc_reclaim.
> 
> Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>

Thanks for catching this, could you please point me to the steps to reproduce
the problem

> ---
> This is fix for memory-cgroup-hierarchical-reclaim-v4.patch.
> 
>  mm/memcontrol.c |   23 +++++++++--------------
>  1 files changed, 9 insertions(+), 14 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index d177ed7..ac445cf 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -468,11 +468,8 @@ unsigned long mem_cgroup_isolate_pages(unsigned long nr_to_scan,
>  	return nr_taken;
>  }
> 
> -static struct mem_cgroup *
> -mem_cgroup_from_res_counter(struct res_counter *counter)
> -{
> -	return container_of(counter, struct mem_cgroup, res);
> -}
> +#define mem_cgroup_from_res_counter(counter, member)	\
> +	container_of(counter, struct mem_cgroup, member)
> 
>  /*
>   * This routine finds the DFS walk successor. This routine should be
> @@ -665,18 +662,16 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm,
>  			/* mem+swap counter fails */
>  			res_counter_uncharge(&mem->res, PAGE_SIZE);
>  			noswap = true;
> -		}
> +			mem_over_limit = mem_cgroup_from_res_counter(fail_res,
> +									memsw);
> +		} else
> +			/* mem counter fails */
> +			mem_over_limit = mem_cgroup_from_res_counter(fail_res,
> +									res);
> +
>  		if (!(gfp_mask & __GFP_WAIT))
>  			goto nomem;
> 
> -		/*
> -		 * Is one of our ancestors over their limit?
> -		 */
> -		if (fail_res)
> -			mem_over_limit = mem_cgroup_from_res_counter(fail_res);
> -		else
> -			mem_over_limit = mem;
> -
>  		ret = mem_cgroup_hierarchical_reclaim(mem_over_limit, gfp_mask,
>  							noswap);
> 

Seems reasonable, but I want to test it.

-- 
	Balbir

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