Re: wake_up_process implied memory barrier clarification

[Peter Zijlstra]

On Thu, Aug 27, 2015 at 02:27:27PM +0200, Michal Hocko wrote:
> 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?

Its true for wake_up(), since that bails early if the waitqueue list is
empty.

I suspect there was no exception made for wake_up_process() to simplify
the rules.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/