wake_up_process implied memory barrier clarification

From: Michal Hocko
Date: Thu Aug 27 2015 - 08:27:34 EST

I have just stumbled over the comment above wake_up_process which
* It may be assumed that this function implies a write memory barrier before
* changing the task state if and only if any tasks are woken up.

but try_to_wake_up does smp_mb__before_spinlock and did smp_wmb
since 04e2f1741d235 unconditionally. The comment was added when the
smp_wmb was in place already so I am wondering whether the comment is

Could somebody clarify please?
Michal Hocko
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