Paul E. McKenney <paul...@linux.vnet.ibm.com> wrote:
> - node = result.terminal_node.node;
> - smp_read_barrier_depends();
> + node = READ_ONCE(result.terminal_node.node); /* Address dependency. */
The main problem I have with this method of annotation is that it's not
obvious there's a barrier there or which side the barrier is.
I think one of the trickiest issues is that a barrier is typically between two
things and we're not making it clear what those two things actually are.
Also, I would say that the most natural interpretation of READ_ONCE() is that
the implicit barrier comes after the read, e.g.:
f = READ_ONCE(stuff->foo);
/* Implied barrier */
look_at(f->a);
look_at(f->b);
I.e. READ_ONCE() prevents stuff->foo from being reread whilst you access f and
orders LOAD(stuff->foo) before LOAD(f->a) and LOAD(f->b).
David
