Re: [PATCH v3 6/6] powerpc: atomic: Implement cmpxchg{,64}_* and atomic{,64}_cmpxchg_* variants

Will Deacon
2015-10-13T15:04:30Z

On Tue, Oct 13, 2015 at 10:58:30PM +0800, Boqun Feng wrote:
> On Tue, Oct 13, 2015 at 03:43:33PM +0100, Will Deacon wrote:
> > Putting a barrier in the middle of that critical section is probably a
> > terrible idea, and that's why I thought you were avoiding it (hence my
>
> The fact is that I haven't thought of that way to implement
> cmpxchg_release before you ask that question ;-) And I'm not going to do
> that for now and probably not in the future.
>
> > original question). Perhaps just add a comment to that effect, since I
>
> Are you suggesting if I put a barrier in the middle I'd better to add a
> comment, right? So if I don't do that, it's OK to let this patch as it.

No, I mean put a comment in your file to explain the reason why you
override _relaxed and _acquire, but not _release (because overriding
_release would introduce this weird barrier in the middle of the critical
section, which would likely cause the conditional store to fail).

Will