On Thu, Jan 28, 2021 at 01:09:39PM +0100, Alexander Sverdlin wrote:
> On 28/01/2021 12:33, Peter Zijlstra wrote:
> > On Thu, Jan 28, 2021 at 08:27:29AM +0100, Alexander Sverdlin wrote:
> >
> >>>> +#define __smp_store_release(p, v) \
> >>>> +do { \
> >>>> + compiletime_assert_atomic_type(*p); \
> >>>> + __smp_wmb(); \
> >>>> + __smp_rmb(); \
> >>>> + WRITE_ONCE(*p, v); \
> >>>> +} while (0)
> I actually hoped you will remember the discussion you've participated 5 years
> ago and (in my understanding) actually already agreed that the solution itself
> is not broken:
>
> https://lore.kernel.org/lkml/20151112180003.GE17308@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
My memory really isn't that good. I can barely remember what I did 5
weeks ago, 5 years ago might as well have never happened.
> Could you please just suggest the proper comment you expect to be added here,
> because there is no doubts, you have much more experience here than me?
So for store_release I'm not too worried, and provided no read
speculation, wmb is indeed sufficient. This is because our store_release
is RCpc.
Something like:
/*
* Because Octeon does not do read speculation, an smp_wmb()
* is sufficient to ensure {load,store}->{store} order.
*/
#define __smp_store_release(p, v) \
do { \
compiletime_assert_atomic_type(*p); \
__smp_wmb(); \
WRITE_ONCE(*p, v); \
} while (0)
