Re: [-mm][PATCH 2/2] Memory rlimit enhance mm_owner_changed callback to deal with exited owner

[Paul Menage]

On Mon, Aug 11, 2008 at 3:07 AM, Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx> wrote:
>
>
> mm_owner_changed callback can also be called with new task set to NULL.
> (race between try_to_unuse() and mm->owner exiting). Surprisingly the order
> of cgroup arguments being passed was incorrect (proves that we did not
> run into mm_owner_changed callback at all).
>
> Signed-off-by: Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx>

Acked-by: Paul Menage <menage@xxxxxxxxxx>


> ---
>
>  mm/memrlimitcgroup.c |   15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
>
> diff -puN mm/memrlimitcgroup.c~memrlimit-handle-mm-owner-notification-with-task-null mm/memrlimitcgroup.c
> --- linux-2.6.27-rc1/mm/memrlimitcgroup.c~memrlimit-handle-mm-owner-notification-with-task-null 2008-08-05 10:56:56.000000000 +0530
> +++ linux-2.6.27-rc1-balbir/mm/memrlimitcgroup.c        2008-08-05 11:24:04.000000000 +0530
> @@ -73,6 +73,12 @@ void memrlimit_cgroup_uncharge_as(struct
>  {
>        struct memrlimit_cgroup *memrcg;
>
> +       /*
> +        * Uncharge happened as a part of the mm_owner_changed callback
> +        */
> +       if (!mm->owner)
> +               return;
> +
>        memrcg = memrlimit_cgroup_from_task(mm->owner);
>        res_counter_uncharge(&memrcg->as_res, (nr_pages << PAGE_SHIFT));
>  }
> @@ -235,8 +241,8 @@ out:
>  * This callback is called with mmap_sem held
>  */
>  static void memrlimit_cgroup_mm_owner_changed(struct cgroup_subsys *ss,
> -                                               struct cgroup *cgrp,
>                                                struct cgroup *old_cgrp,
> +                                               struct cgroup *cgrp,
>                                                struct task_struct *p)
>  {
>        struct memrlimit_cgroup *memrcg, *old_memrcg;
> @@ -246,7 +252,12 @@ static void memrlimit_cgroup_mm_owner_ch
>        memrcg = memrlimit_cgroup_from_cgrp(cgrp);
>        old_memrcg = memrlimit_cgroup_from_cgrp(old_cgrp);
>
> -       if (res_counter_charge(&memrcg->as_res, (mm->total_vm << PAGE_SHIFT)))
> +       /*
> +        * If we don't have a new cgroup, we just uncharge from the old one.
> +        * It means that the task is going away
> +        */
> +       if (memrcg &&
> +           res_counter_charge(&memrcg->as_res, (mm->total_vm << PAGE_SHIFT)))
>                goto out;
>        res_counter_uncharge(&old_memrcg->as_res, (mm->total_vm << PAGE_SHIFT));
>  out:
> _
>
> --
>        Warm Regards,
>        Balbir Singh
>        Linux Technology Center
>        IBM, ISTL
>
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