wake_up_process implied memory barrier clarification

Michal Hocko
2015-08-27T12:27:31Z

Hi,
I have just stumbled over the comment above wake_up_process which
claims:
"
* 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
wrong/misleading.

Could somebody clarify please?
--
Michal Hocko
SUSE Labs