linux-kernel - Re: [PATCH v2] introduce atomic_pointer to fix a race condition in cancelable mcs spinlocks

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Date:	Fri, 06 Jun 2014 08:42:19 -0700
From:	Davidlohr Bueso <davidlohr@...com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Mikulas Patocka <mpatocka@...hat.com>,
	"James E.J. Bottomley" <jejb@...isc-linux.org>,
	Helge Deller <deller@....de>,
	John David Anglin <dave.anglin@...l.net>,
	Parisc List <linux-parisc@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	"Vinod, Chegu" <chegu_vinod@...com>,
	Waiman Long <Waiman.Long@...com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Anvin <hpa@...or.com>, Andi Kleen <andi@...stfloor.org>,
	"Chandramouleeswaran, Aswin" <aswin@...com>,
	"Norton, Scott J" <scott.norton@...com>,
	Jason Low <jason.low2@...com>, mingo@...nel.org
Subject: Re: [PATCH v2] introduce atomic_pointer to fix a race condition in
 cancelable mcs spinlocks

On Fri, 2014-06-06 at 17:06 +0200, Peter Zijlstra wrote:
> On Mon, Jun 02, 2014 at 10:09:35AM -0700, Linus Torvalds wrote:
> > On Mon, Jun 2, 2014 at 9:25 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> > >
> > > And I can't say I'm a particular fan of these ops either, as alternative
> > > I'm almost inclined to just exclude parisc from using opt spinning.
> > 
> > Please do.
> 
> Something like so; if the rwsem stuff lands in .15 we need more for
> that, it doesn't have a convenient CONFIG symbol like this.
> 
> Linus will you take this from email, or should I get it through
> tip/locking/urgent or so?
> 
> ---
> Subject: locking, mutex: Disable optimistic spinning for PA-RISC
> 
> PA-RISC's cmpxchg is not save against normal stores and the code used
> for optimistic spinning is known broken because of this.
> 
> Disable for now.

I almost hit the send button :)

> 
> Reported-by: Mikulas Patocka <mpatocka@...hat.com>
> Signed-off-by: Peter Zijlstra <peterz@...radead.org>
> ---

Reviewed-by: Davidlohr Bueso <davidlohr@...com>

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