Re: [PATCH tip/core/rcu 16/27] rcu: Add comment documenting how rcu_seq_snap works

Paul E. McKenney
2018-06-26T18:07:00Z

On Tue, Jun 26, 2018 at 07:14:54PM +0200, Peter Zijlstra wrote:
> On Mon, Jun 25, 2018 at 05:35:02PM -0700, Paul E. McKenney wrote:
> > From: "Joel Fernandes (Google)" <joel@joelfernandes.org>
> >
> > rcu_seq_snap may be tricky to decipher. Lets document how it works with
> > an example to make it easier.
>
> Since you had me looking at them functions; why isn't rcu_seq_snap()
> using smp_load_acquire() and rcu_seq_end() using smp_store_release() ?
> Their respective comments seem to suggest that would be sufficent.

I do not believe that this would suffice. Would it make sense to refer
to Documentation/RCU/Design/Memory-Ordering in the comment header?

Except that this would invite sprinkling this pathname far and wide...

The key point is that these functions are part of the any-to-any
memory-ordering guarantee that RCU grace periods provide.

Thanx, Paul