Re: mm: deadlock between get_online_cpus/pcpu_alloc

[Christoph Lameter]

On Thu, 9 Feb 2017, Michal Hocko wrote:

> Christoph, you are completely ignoring the reality and the code. There
> is no need for stop_machine nor it is helping anything. As the matter
> of fact there is a synchronization with the cpu hotplug needed if you
> want to make a per-cpu specific operations. get_online_cpus is the
> most straightforward and heavy weight way to do this synchronization
> but not the only one. As the patch [1] describes we do not really need
> get_online_cpus in drain_all_pages because we can do _better_. But
> this is not in any way a generic thing applicable to other code paths.
>
> If you disagree then you are free to post patches but hand waving you
> are doing here is just wasting everybody's time. So please cut it here
> unless you have specific proposals to improve the current situation.

I am fine with the particular solution here for this particular problem.

My problem is the general way of having to synchronize via
get_online_cpus() because of cpu hotplug operations.