netfilter: nft_set_pipapo: prepare destroy function for on-demand clone

Once priv->clone can be NULL in case no insertions/removals occurred
in the last transaction we need to drop set elements from priv->match
if priv->clone is NULL.

While at it, condense this function by reusing the pipapo_free_match
helper instead of open-coded version.

The rcu_barrier() is removed, its not needed: old call_rcu instances
for pipapo_reclaim_match do not access struct nft_set.
Signed-off-by: Florian Westphal <fw@strlen.de>
Reviewed-by: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nft_set_pipapo.c

@@ -2326,33 +2326,18 @@ static void nft_pipapo_destroy(const struct nft_ctx *ctx,
 {
 	struct nft_pipapo *priv = nft_set_priv(set);
 	struct nft_pipapo_match *m;
-	int cpu;
 
 	m = rcu_dereference_protected(priv->match, true);
-	if (m) {
-		rcu_barrier();
-
-		for_each_possible_cpu(cpu)
-			pipapo_free_scratch(m, cpu);
-		free_percpu(m->scratch);
-		pipapo_free_fields(m);
-		kfree(m);
-		priv->match = NULL;
-	}
 
 	if (priv->clone) {
-		m = priv->clone;
-
-		nft_set_pipapo_match_destroy(ctx, set, m);
-
-		for_each_possible_cpu(cpu)
-			pipapo_free_scratch(priv->clone, cpu);
-		free_percpu(priv->clone->scratch);
-
-		pipapo_free_fields(priv->clone);
-		kfree(priv->clone);
+		nft_set_pipapo_match_destroy(ctx, set, priv->clone);
+		pipapo_free_match(priv->clone);
 		priv->clone = NULL;
+	} else {
+		nft_set_pipapo_match_destroy(ctx, set, m);
 	}
+
+	pipapo_free_match(m);
 }
 
 /**