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Date: Mon, 19 Jan 2015 16:30:08 -0800
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Peter Hurley <peter@hurleysoftware.com>
Cc: Peter Zijlstra <peterz@infradead.org>, Kent Overstreet <kmo@daterainc.com>,
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        Linus Torvalds <torvalds@linux-foundation.org>,
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Subject: Re: Linux 3.19-rc3
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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