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Date: Tue, 16 Mar 2010 14:13:36 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Nick Piggin <npiggin@suse.de>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
       Linus Torvalds <torvalds@linux-foundation.org>,
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       linux-kernel@vger.kernel.org, Chris Friesen <cfriesen@nortel.com>,
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Subject: Re: [PATCH -tip] introduce sys_membarrier(): process-wide memory
 barrier (v9)
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* 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