Re: [PATCH 1/2] mm: memcg: switch to css_tryget() in get_mem_cgroup_from_mm()

On Thu 14-11-19 11:20:18, Tejun Heo wrote:

Hello,

On Thu, Nov 14, 2019 at 08:16:57PM +0100, Michal Hocko wrote:

...

Then what is the point of this function and what about all other users?

It is useful for controlling admissions of new userspace visible uses

• e.g. a tracepoint shouldn't be allowed to be attached to a cgroup

which has already been deleted.

I am not sure I understand. Roman says that the cgroup can get offline right after the function returns. How is "already deleted" different from "just deleted"? I thought that the state is preserved at least while the rcu lock is held but my memory is dim here.

We're just using it too liberally.

Can we get a doc update to be explicit about sensible usecases so that others can be dropped accordingly?