xfrm6_tunnel: Fix potential panic when unloading xfrm6_tunnel module

When unloading xfrm6_tunnel module, xfrm6_tunnel_fini directly
frees the xfrm6_tunnel_spi_kmem. Maybe someone has gotten the
xfrm6_tunnel_spi, so need to wait it.

Fixes: 91cc3bb("xfrm6_tunnel: RCU conversion")
Signed-off-by: Su Yanjun <[email protected]>
Acked-by: Herbert Xu <[email protected]>
Signed-off-by: Steffen Klassert <[email protected]>

Author: suyj-fnst

net/ipv6/xfrm6_tunnel.c

@@ -402,6 +402,10 @@ static void __exit xfrm6_tunnel_fini(void)
 	xfrm6_tunnel_deregister(&xfrm6_tunnel_handler, AF_INET6);
 	xfrm_unregister_type(&xfrm6_tunnel_type, AF_INET6);
 	unregister_pernet_subsys(&xfrm6_tunnel_net_ops);
+	/* Someone maybe has gotten the xfrm6_tunnel_spi.
+	 * So need to wait it.
+	 */
+	rcu_barrier();
 	kmem_cache_destroy(xfrm6_tunnel_spi_kmem);
 }