Re: [PATCH RFC v2] rcu/segcblist: Add counters to segcblist datastructure

[Joel Fernandes]

On Sat, Jul 18, 2020 at 11:55 PM Joel Fernandes (Google)
<joel@xxxxxxxxxxxxxxxxx> wrote:
[...]
>         /* If no callbacks moved, nothing more need be done. */
> @@ -419,10 +494,9 @@ void rcu_segcblist_advance(struct rcu_segcblist *rsclp, unsigned long seq)
>          * callbacks.  The overall effect is to copy down the later pointers
>          * into the gap that was created by the now-ready segments.
>          */
> -       for (j = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++, j++) {
> -               if (rsclp->tails[j] == rsclp->tails[RCU_NEXT_TAIL])
> -                       break;  /* No more callbacks. */
> +       for (j = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL && j < RCU_NEXT_TAIL; i++, j++) {
>                 WRITE_ONCE(rsclp->tails[j], rsclp->tails[i]);
> +               rcu_segcblist_move_seglen(rsclp, i, j);
>                 rsclp->gp_seq[j] = rsclp->gp_seq[i];
>         }

Unfortunately I broke this code, _sigh_.  I need to reinstate the
if (rsclp->tails[j] == rsclp->tails[RCU_NEXT_TAIL]) , I completely
misunderstood that.