net/tls: narrow down the critical area of device_offload_lock

On setsockopt path we need to hold device_offload_lock from
the moment we check netdev is up until the context is fully
ready to be added to the tls_device_list.

No need to hold it around the get_netdev_for_sock().
Change the code and remove the confusing comment.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: John Hurley <john.hurley@netronome.com>
Reviewed-by: Dirk van der Merwe <dirk.vandermerwe@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tls/tls_device.c

@@ -935,17 +935,11 @@ int tls_set_device_offload(struct sock *sk, struct tls_context *ctx)
 	if (skb)
 		TCP_SKB_CB(skb)->eor = 1;
 
-	/* We support starting offload on multiple sockets
-	 * concurrently, so we only need a read lock here.
-	 * This lock must precede get_netdev_for_sock to prevent races between
-	 * NETDEV_DOWN and setsockopt.
-	 */
-	down_read(&device_offload_lock);
 	netdev = get_netdev_for_sock(sk);
 	if (!netdev) {
 		pr_err_ratelimited("%s: netdev not found\n", __func__);
 		rc = -EINVAL;
-		goto release_lock;
+		goto disable_cad;
 	}
 
 	if (!(netdev->features & NETIF_F_HW_TLS_TX)) {
@@ -956,10 +950,15 @@ int tls_set_device_offload(struct sock *sk, struct tls_context *ctx)
 	/* Avoid offloading if the device is down
 	 * We don't want to offload new flows after
 	 * the NETDEV_DOWN event
+	 *
+	 * device_offload_lock is taken in tls_devices's NETDEV_DOWN
+	 * handler thus protecting from the device going down before
+	 * ctx was added to tls_device_list.
 	 */
+	down_read(&device_offload_lock);
 	if (!(netdev->flags & IFF_UP)) {
 		rc = -EINVAL;
-		goto release_netdev;
+		goto release_lock;
 	}
 
 	ctx->priv_ctx_tx = offload_ctx;
@@ -967,9 +966,10 @@ int tls_set_device_offload(struct sock *sk, struct tls_context *ctx)
 					     &ctx->crypto_send.info,
 					     tcp_sk(sk)->write_seq);
 	if (rc)
-		goto release_netdev;
+		goto release_lock;
 
 	tls_device_attach(ctx, sk, netdev);
+	up_read(&device_offload_lock);
 
 	/* following this assignment tls_is_sk_tx_device_offloaded
 	 * will return true and the context might be accessed
@@ -977,14 +977,14 @@ int tls_set_device_offload(struct sock *sk, struct tls_context *ctx)
 	 */
 	smp_store_release(&sk->sk_validate_xmit_skb, tls_validate_xmit_skb);
 	dev_put(netdev);
-	up_read(&device_offload_lock);
 
 	return 0;
 
-release_netdev:
-	dev_put(netdev);
 release_lock:
 	up_read(&device_offload_lock);
+release_netdev:
+	dev_put(netdev);
+disable_cad:
 	clean_acked_data_disable(inet_csk(sk));
 	crypto_free_aead(offload_ctx->aead_send);
 free_rec_seq:
@@ -1008,17 +1008,10 @@ int tls_set_device_offload_rx(struct sock *sk, struct tls_context *ctx)
 	if (ctx->crypto_recv.info.version != TLS_1_2_VERSION)
 		return -EOPNOTSUPP;
 
-	/* We support starting offload on multiple sockets
-	 * concurrently, so we only need a read lock here.
-	 * This lock must precede get_netdev_for_sock to prevent races between
-	 * NETDEV_DOWN and setsockopt.
-	 */
-	down_read(&device_offload_lock);
 	netdev = get_netdev_for_sock(sk);
 	if (!netdev) {
 		pr_err_ratelimited("%s: netdev not found\n", __func__);
-		rc = -EINVAL;
-		goto release_lock;
+		return -EINVAL;
 	}
 
 	if (!(netdev->features & NETIF_F_HW_TLS_RX)) {
@@ -1029,16 +1022,21 @@ int tls_set_device_offload_rx(struct sock *sk, struct tls_context *ctx)
 	/* Avoid offloading if the device is down
 	 * We don't want to offload new flows after
 	 * the NETDEV_DOWN event
+	 *
+	 * device_offload_lock is taken in tls_devices's NETDEV_DOWN
+	 * handler thus protecting from the device going down before
+	 * ctx was added to tls_device_list.
 	 */
+	down_read(&device_offload_lock);
 	if (!(netdev->flags & IFF_UP)) {
 		rc = -EINVAL;
-		goto release_netdev;
+		goto release_lock;
 	}
 
 	context = kzalloc(TLS_OFFLOAD_CONTEXT_SIZE_RX, GFP_KERNEL);
 	if (!context) {
 		rc = -ENOMEM;
-		goto release_netdev;
+		goto release_lock;
 	}
 	context->resync_nh_reset = 1;
 
@@ -1066,10 +1064,10 @@ int tls_set_device_offload_rx(struct sock *sk, struct tls_context *ctx)
 	down_read(&device_offload_lock);
 release_ctx:
 	ctx->priv_ctx_rx = NULL;
-release_netdev:
-	dev_put(netdev);
 release_lock:
 	up_read(&device_offload_lock);
+release_netdev:
+	dev_put(netdev);
 	return rc;
 }