Re: [PATCH v8 2/6] rcu/segcblist: Add counters to segcblist datastructure

[Frederic Weisbecker]

On Wed, Oct 21, 2020 at 03:08:09PM -0400, Joel Fernandes (Google) wrote:
> @@ -307,6 +317,7 @@ void rcu_segcblist_extract_done_cbs(struct rcu_segcblist 
> *rsclp,
>  
>       if (!rcu_segcblist_ready_cbs(rsclp))
>               return; /* Nothing to do. */
> +     rclp->len = rcu_segcblist_get_seglen(rsclp, RCU_DONE_TAIL);

I realize, doesn't it break the unsegmented count in srcu_invoke_callbacks() ?

It still does rcu_segcblist_insert_count(), so it adds zero to rsclp->len
which thus doesn't get cleared and probably keeps growing.

At least srcu_barrier() relies on it. And module exit should warn.

>       *rclp->tail = rsclp->head;
>       WRITE_ONCE(rsclp->head, *rsclp->tails[RCU_DONE_TAIL]);
>       WRITE_ONCE(*rsclp->tails[RCU_DONE_TAIL], NULL);
> @@ -314,6 +325,7 @@ void rcu_segcblist_extract_done_cbs(struct rcu_segcblist 
> *rsclp,
>       for (i = RCU_CBLIST_NSEGS - 1; i >= RCU_DONE_TAIL; i--)
>               if (rsclp->tails[i] == rsclp->tails[RCU_DONE_TAIL])
>                       WRITE_ONCE(rsclp->tails[i], &rsclp->head);
> +     rcu_segcblist_set_seglen(rsclp, RCU_DONE_TAIL, 0);
>  }
>  
>  /*
> @@ -330,11 +342,16 @@ void rcu_segcblist_extract_pend_cbs(struct 
> rcu_segcblist *rsclp,
>  
>       if (!rcu_segcblist_pend_cbs(rsclp))
>               return; /* Nothing to do. */
> +     rclp->len = rcu_segcblist_get_seglen(rsclp, RCU_WAIT_TAIL) +
> +                 rcu_segcblist_get_seglen(rsclp, RCU_NEXT_READY_TAIL) +
> +                 rcu_segcblist_get_seglen(rsclp, RCU_NEXT_TAIL);
>       *rclp->tail = *rsclp->tails[RCU_DONE_TAIL];
>       rclp->tail = rsclp->tails[RCU_NEXT_TAIL];
>       WRITE_ONCE(*rsclp->tails[RCU_DONE_TAIL], NULL);
> -     for (i = RCU_DONE_TAIL + 1; i < RCU_CBLIST_NSEGS; i++)
> +     for (i = RCU_DONE_TAIL + 1; i < RCU_CBLIST_NSEGS; i++) {
>               WRITE_ONCE(rsclp->tails[i], rsclp->tails[RCU_DONE_TAIL]);
> +             rcu_segcblist_set_seglen(rsclp, i, 0);

You seem to have forgotten the suggestion?

    rclp->len += rcu_segcblist_get_seglen(rsclp, i)


Thanks.