net: decrease cached dst counters in dst_release

Upstream fix ac888d5 ("net: do not delay dst_entries_add() in
dst_release()") moved decrementing the dst count from dst_destroy to
dst_release to avoid accessing already freed data in case of netns
dismantle. However in case CONFIG_DST_CACHE is enabled and OvS+tunnels
are used, this fix is incomplete as the same issue will be seen for
cached dsts:

  Unable to handle kernel paging request at virtual address ffff5aabf6b5c000
  Call trace:
   percpu_counter_add_batch+0x3c/0x160 (P)
   dst_release+0xec/0x108
   dst_cache_destroy+0x68/0xd8
   dst_destroy+0x13c/0x168
   dst_destroy_rcu+0x1c/0xb0
   rcu_do_batch+0x18c/0x7d0
   rcu_core+0x174/0x378
   rcu_core_si+0x18/0x30

Fix this by invalidating the cache, and thus decrementing cached dst
counters, in dst_release too.

Fixes: d71785f ("net: add dst_cache to ovs vxlan lwtunnel")
Signed-off-by: Antoine Tenart <atenart@kernel.org>
Link: https://patch.msgid.link/20250326173634.31096-1-atenart@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

net/core/dst.c

@@ -165,6 +165,14 @@ static void dst_count_dec(struct dst_entry *dst)
 void dst_release(struct dst_entry *dst)
 {
 	if (dst && rcuref_put(&dst->__rcuref)) {
+#ifdef CONFIG_DST_CACHE
+		if (dst->flags & DST_METADATA) {
+			struct metadata_dst *md_dst = (struct metadata_dst *)dst;
+
+			if (md_dst->type == METADATA_IP_TUNNEL)
+				dst_cache_reset_now(&md_dst->u.tun_info.dst_cache);
+		}
+#endif
 		dst_count_dec(dst);
 		call_rcu_hurry(&dst->rcu_head, dst_destroy_rcu);
 	}