Date: Mon, 6 Nov 2006 16:17:56 -0500 (EST)
From: Steven Rostedt <rostedt@goodmis.org>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
cc: Linus Torvalds <torvalds@osdl.org>, Oleg Nesterov <oleg@tv-sign.ru>,
       Thomas Gleixner <tglx@linutronix.de>, Andrew Morton <akpm@osdl.org>,
       linux-kernel@vger.kernel.org
Subject: Re: PATCH? hrtimer_wakeup: fix a theoretical race wrt rt_mutex_slowlock()
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On Tue, 7 Nov 2006, Benjamin Herrenschmidt wrote:

> On Mon, 2006-11-06 at 07:35 -0500, Steven Rostedt wrote:
>
> > It is relevant.  In powerpc, can one write happen before another write?
> >
> >
> >   x = 1;
> >   barrier();  (only compiler barrier)
> >   b = 2;
> >
> >
> > And have CPU 2 see b=2 before seeing x=1?
>
> Yes. Definitely.

OK, I see in powerpc, that spin lock calls isync. This just clears the
pipeline. It doesn't touch the loads and stores, right?

So basically saying this:

   x=1;
   asm ("isync");
   b=2;

Would that have the same problem too?  Where another CPU can see x=1
before seeing b=2?

Thanks!

-- Steve

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