Re: [PATCH] It may not be assumed that wake_up(), finish_wait() andco. imply a memory barrier

[Linus Torvalds]

On Thu, 23 Apr 2009, David Howells wrote:
> 
> Well, Ingo's point is it could be left up to the caller of wake_up() to supply
> the barrier:
> 
> 	*my_variable = 1234;
> 	smp_wmb();
> 	wake_up(&my_queue);

That's bogus.

EVERY SINGLE wake_up() would need it.

There is _always_ a reason for the wakeup. And yes, you can re-order 
things, but we normally don't. Just make the rule be that there's an 
implied smp_wmb() instead.

It's not like it's going to cost anything on any sane architecture anyway. 
So asking people to add "smp_wmb()" calls before their wakups just makes 
the source code unreadable and fragile, for no actual advantage.

		Linus
--
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/