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

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Message-ID: <20140602164655.GT22231@linux.vnet.ibm.com>
Date:	Mon, 2 Jun 2014 09:46:55 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Mikulas Patocka <mpatocka@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	jejb@...isc-linux.org, deller@....de,
	John David Anglin <dave.anglin@...l.net>,
	linux-parisc@...r.kernel.org, linux-kernel@...r.kernel.org,
	chegu_vinod@...com, Waiman.Long@...com, tglx@...utronix.de,
	riel@...hat.com, akpm@...ux-foundation.org, davidlohr@...com,
	hpa@...or.com, andi@...stfloor.org, aswin@...com,
	scott.norton@...com, Jason Low <jason.low2@...com>
Subject: Re: [PATCH v2] introduce atomic_pointer to fix a race condition in
 cancelable mcs spinlocks

On Mon, Jun 02, 2014 at 06:30:32PM +0200, Peter Zijlstra wrote:
> On Mon, Jun 02, 2014 at 06:25:25PM +0200, Peter Zijlstra wrote:
> > I'm almost inclined to just exclude parisc from using opt spinning.
> > 
> > That said, this patch still doesn't address the far more interesting
> > problem of actually finding these issues for these few weird archs.
> 
> So why do these archs provide xchg() and cmpxchg() at all? Wouldn't it
> be much simpler if archs that cannot sanely do this, not provide these
> primitives at all?

Such architectures would also need to avoid NO_HZ_FULL_SYSIDLE and
RCU_NOCB_CPU, but those are probably entirely reasonable restrictions.

							Thanx, Paul

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