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

[Peter Zijlstra]

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);