bpf: offload: free prog->aux->offload when device disappears

All bpf offload operations should now be under bpf_devs_lock,
it's safe to free and clear the entire offload structure,
not only the netdev pointer.

__bpf_prog_offload_destroy() will no longer be called multiple
times.
Suggested-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

kernel/bpf/offload.c

@@ -70,12 +70,14 @@ int bpf_prog_offload_init(struct bpf_prog *prog, union bpf_attr *attr)
 static int __bpf_offload_ndo(struct bpf_prog *prog, enum bpf_netdev_command cmd,
 			     struct netdev_bpf *data)
 {
-	struct net_device *netdev = prog->aux->offload->netdev;
+	struct bpf_dev_offload *offload = prog->aux->offload;
+	struct net_device *netdev;
 
 	ASSERT_RTNL();
 
-	if (!netdev)
+	if (!offload)
 		return -ENODEV;
+	netdev = offload->netdev;
 	if (!netdev->netdev_ops->ndo_bpf)
 		return -EOPNOTSUPP;
 
@@ -111,7 +113,7 @@ int bpf_prog_offload_verify_insn(struct bpf_verifier_env *env,
 
 	down_read(&bpf_devs_lock);
 	offload = env->prog->aux->offload;
-	if (offload->netdev)
+	if (offload)
 		ret = offload->dev_ops->insn_hook(env, insn_idx, prev_insn_idx);
 	up_read(&bpf_devs_lock);
 
@@ -123,31 +125,24 @@ static void __bpf_prog_offload_destroy(struct bpf_prog *prog)
 	struct bpf_dev_offload *offload = prog->aux->offload;
 	struct netdev_bpf data = {};
 
-	/* Caution - if netdev is destroyed before the program, this function
-	 * will be called twice.
-	 */
-
 	data.offload.prog = prog;
 
 	if (offload->dev_state)
 		WARN_ON(__bpf_offload_ndo(prog, BPF_OFFLOAD_DESTROY, &data));
 
-	offload->dev_state = false;
 	list_del_init(&offload->offloads);
-	offload->netdev = NULL;
+	kfree(offload);
+	prog->aux->offload = NULL;
 }
 
 void bpf_prog_offload_destroy(struct bpf_prog *prog)
 {
-	struct bpf_dev_offload *offload = prog->aux->offload;
-
 	rtnl_lock();
 	down_write(&bpf_devs_lock);
+	if (prog->aux->offload)
 		__bpf_prog_offload_destroy(prog);
 	up_write(&bpf_devs_lock);
 	rtnl_unlock();
-
-	kfree(offload);
 }
 
 static int bpf_prog_offload_translate(struct bpf_prog *prog)