Re: Linux 3.19-rc3

Peter Hurley
2015-01-20T14:03:17Z

On 01/19/2015 07:30 PM, Paul E. McKenney wrote:
> 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?

Hi Paul,

As you pointed out, atomic_ops.txt is for arch implementors, so I wasn't
planning on patching that file.

I've been meaning to write up something specifically for everyone else but
my own bugs have kept me from that. [That, and I'm not sure what I write
will be suitable for Documentation.]

Regards,
Peter Hurley