linux-kernel - Re: [PATCH RFC] locking: Add volatile to arch_spinlock

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Message-ID: <20141204201205.GA27787@linux.vnet.ibm.com>
Date:	Thu, 4 Dec 2014 12:12:05 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	Davidlohr Bueso <dave@...olabs.net>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH RFC] locking: Add volatile to arch_spinlock_t structures

On Thu, Dec 04, 2014 at 12:00:52PM -0800, Paul E. McKenney wrote:

[ . . . ]

> So any compiler that clobbers some adjacent non-bitfield variable or
> field that is accessible by other threads is not just despicable, it
> fails to conform to the standard.
> 
> Whew!  ;-)

And part of the reason for my confusion is that I am using an old version
of gcc, 4.6.3.  Apparently this aspect of gcc wasn't fixed until 4.7
or thereabouts.

							Thanx, Paul

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