linux-kernel - Re: [PATCH RFC v2 1/2] qspinlock: Introducing a 4-byte queue spinlock implementation

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Message-ID: <20130828130529.GP10002@twins.programming.kicks-ass.net>
Date:	Wed, 28 Aug 2013 15:05:29 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Alexander Fyodorov <halcy@...dex.ru>,
	Waiman Long <waiman.long@...com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"Chandramouleeswaran, Aswin" <aswin@...com>,
	"Norton, Scott J" <scott.norton@...com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH RFC v2 1/2] qspinlock: Introducing a 4-byte queue
 spinlock implementation

On Wed, Aug 28, 2013 at 08:59:57AM -0400, Steven Rostedt wrote:
> On Wed, 28 Aug 2013 10:19:37 +0200
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> 
> > > An unlock followed by a lock needs to act like a full barrier, but there
> > > is no requirement that a lock or unlock taken separately act like a
> > > full barrier.
> > 
> > But that is already a property of the acquisition/release barrier.
> 
> As I mentioned in my fixes for the -rt swait barrier patches I sent.

Not to me you didn't ;-)

> Spin locks only prevent leaks out of the critical section. It does not
> guarantee leaks into the critical section, thus:

What's your point? You're just re-iterating the semantics in case
anybody forgot about them?
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