Re: mm: deadlock between get_online_cpus/pcpu_alloc

[Christoph Lameter]

On Wed, 8 Feb 2017, Michal Hocko wrote:

> > Huch? stop_machine() is horrible and heavy weight. Don't go there, there
> > must be simpler solutions than that.
>
> Absolutely agreed. We are in the page allocator path so using the
> stop_machine* is just ridiculous. And, in fact, there is a much simpler
> solution [1]

That is nonsense. stop_machine would be used when adding removing a
processor. There would be no need to synchronize when looping over active
cpus anymore. get_online_cpus() etc would be removed from the hot
path since the cpu masks are guaranteed to be stable.