On Wed 08-02-17 09:11:06, Cristopher Lameter wrote:

On Wed, 8 Feb 2017, Michal Hocko wrote:

quoted

quoted

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.

I have no idea what you are trying to say and how this is related to the
deadlock we are discussing here. We certainly do not need to add
stop_machine the problem. And yeah, dropping get_online_cpus was
possible after considering all fallouts.

-- 
Michal Hocko
SUSE Labs

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