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

Balbir Singh
2008-11-22T14:03:44Z

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