Re: [PATCH v4 07/15] lockdep: Implement crossrelease feature

Peter Zijlstra
2017-01-16T15:13:27Z

On Fri, Dec 09, 2016 at 02:12:03PM +0900, Byungchul Park wrote:
> + /*
> + * We assign class_idx here redundantly even though following
> + * memcpy will cover it, in order to ensure a rcu reader can
> + * access the class_idx atomically without lock.
> + *
> + * Here we assume setting a word-sized variable is atomic.

which one, where?

> + */
> + xlock->hlock.class_idx = hlock->class_idx;
> + gen_id = (unsigned int)atomic_inc_return(&cross_gen_id);
> + WRITE_ONCE(xlock->gen_id, gen_id);
> + memcpy(&xlock->hlock, hlock, sizeof(struct held_lock));
> + INIT_LIST_HEAD(&xlock->xlock_entry);
> + list_add_tail_rcu(&xlock->xlock_entry, &xlocks_head);