linux-kernel - Re: Linux 3.19-rc3

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Message-ID: <20150120003008.GA14445@linux.vnet.ibm.com>
Date:	Mon, 19 Jan 2015 16:30:08 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Peter Hurley <peter@...leysoftware.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Kent Overstreet <kmo@...erainc.com>,
	Sedat Dilek <sedat.dilek@...il.com>,
	Dave Jones <davej@...emonkey.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, Chris Mason <clm@...com>
Subject: Re: Linux 3.19-rc3

On Tue, Jan 06, 2015 at 12:47:53PM -0800, Paul E. McKenney wrote:
> On Tue, Jan 06, 2015 at 02:57:37PM -0500, Peter Hurley wrote:

[ . . . ]

> David Miller's call, actually.
> 
> But the rule is that if it is an atomic read-modify-write operation and it
> returns a value, then the operation itself needs to include full memory
> barriers before and after (as in the caller doesn't need to add them).
> Otherwise, the operation does not need to include memory ordering.
> Since xchg(), atomic_xchg(), and atomic_long_xchg() all return a value,
> their implementations must include full memory barriers before and after.
> 
> Pretty straightforward.  ;-)

Hello again, Peter,

Were you going to push a patch clarifying this?

							Thanx, Paul

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