linux-kernel - Re: PATCH? hrtimer_wakeup: fix a theoretical race wrt rt_mutex

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Message-ID: <Pine.LNX.4.58.0611061609340.22166@gandalf.stny.rr.com>
Date:	Mon, 6 Nov 2006 16:17:56 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
cc:	Linus Torvalds <torvalds@...l.org>,
	Oleg Nesterov <oleg@...sign.ru>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...l.org>, linux-kernel@...r.kernel.org
Subject: Re: PATCH? hrtimer_wakeup: fix a theoretical race wrt rt_mutex_slowlock()


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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