Re: Linux 3.19-rc3

Paul E. McKenney
2015-01-20T00:30:19Z

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