Re: [PATCH v5 2/4] rcu: Reduce synchronize_rcu() latency

Frederic Weisbecker
2024-02-27T16:15:10Z

Le Tue, Feb 20, 2024 at 07:31:13PM +0100, Uladzislau Rezki (Sony) a écrit :
> +static struct llist_node *rcu_sr_get_wait_head(void)
> +{
> + struct sr_wait_node *sr_wn;
> + int i;
> +
> + for (i = 0; i < SR_NORMAL_GP_WAIT_HEAD_MAX; i++) {
> + sr_wn = &(rcu_state.srs_wait_nodes)[i];
> +
> + if (!atomic_cmpxchg_acquire(&sr_wn->inuse, 0, 1))
> + return &sr_wn->node;
> + }
> +
> + return NULL;
> +}
> +
> +static void rcu_sr_put_wait_head(struct llist_node *node)
> +{
> + struct sr_wait_node *sr_wn = container_of(node, struct sr_wait_node, node);
> + atomic_set_release(&sr_wn->inuse, 0);

Can we comment this release/acquire pair?

IIUC, the point is that we must make sure that the wait_head->next fetch
happens before it gets reused and rewritten to something else.

Thanks.