Re: [PATCH -tip] introduce sys_membarrier(): process-wide memory barrier (v9)

[Ingo Molnar <mingo@elte.hu>]

* Nick Piggin <npiggin@suse.de> wrote:

> On Tue, Mar 16, 2010 at 08:36:35AM +0100, Ingo Molnar wrote:
> > 
> > * Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote:
> > 
> > > Unless this question is answered, Ingo's SA_RUNNING signal proposal, as 
> > > appealing as it may look at a first glance, falls into the 
> > > "fundamentally broken" category. [...]
> > 
> > How is it different from your syscall? I.e. which lines of code make the 
> > difference? We could certainly apply the (trivial) barrier change to 
> > context_switch().
> 
> I think it is just easy for userspace to misuse or think it does something 
> that it doesn't (because of races).

That wasnt my question though. The question i asked Mathieu was to show how 
SA_RUNNING is "fundamentally broken" for librcu use while sys_membarrier() is 
not?

This is really what he claims above. (i preserved the quote)

It must be a misunderstanding either on my side or on his side. (Once that is 
cleared we can discuss further usecases for SA_RUNNING.)

Thanks,

	Ingo