Re: [PATCH -v2 3/6] memcg: mm == NULL is not allowed formem_cgroup_try_charge_mm

[Johannes Weiner]

On Tue, Feb 04, 2014 at 02:28:57PM +0100, Michal Hocko wrote:
> An ancient comment tries to explain that a given mm might be NULL when a
> task is migrated. It has been introduced by 8a9f3ccd (Memory controller:
> memory accounting) along with other bigger changes so it is not much
> more specific about the conditions.
> 
> Anyway, Even if the task is migrated to another memcg there is no way we
> can see NULL mm struct. So either this was not correct from the very
> beginning or it is not true anymore.
> The only remaining case would be seeing charges after exit_mm but that
> would be a bug on its own as the task doesn't have an address space
> anymore.
> 
> This patch replaces the check by VM_BUG_ON to make it obvious that we
> really expect non-NULL mm_struct.
> 
> Signed-off-by: Michal Hocko <mhocko@xxxxxxx>

Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
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