Re: [RFC][PATCH 2/4] memcg: fix error path of mem_cgroup_move_parent

[KAMEZAWA Hiroyuki]

Daisuke Nishimura said:
> There is a bug in error path of mem_cgroup_move_parent.
>
> Extra refcnt got from try_charge should be dropped, and usages incremented
> by try_charge should be decremented in both error paths:
>
>     A: failure at get_page_unless_zero
>     B: failure at isolate_lru_page
>
> This bug makes this parent directory unremovable.
>
> In case of A, rmdir doesn't return, because res.usage doesn't go
> down to 0 at mem_cgroup_force_empty even after all the pc in
> lru are removed.
> In case of B, rmdir fails and returns -EBUSY, because it has
> extra ref counts even after res.usage goes down to 0.
>
>
> Signed-off-by: Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx>
Thank you for catching.

Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>


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