Commit 736f16de authored by Dongli Zhang's avatar Dongli Zhang Committed by David S. Miller
Browse files

net: tap: track dropped skb via kfree_skb_reason() 



The TAP can be used as vhost-net backend. E.g., the tap_handle_frame() is
the interface to forward the skb from TAP to vhost-net/virtio-net.

However, there are many "goto drop" in the TAP driver. Therefore, the
kfree_skb_reason() is involved at each "goto drop" to help userspace
ftrace/ebpf to track the reason for the loss of packets.

The below reasons are introduced:

- SKB_DROP_REASON_SKB_CSUM
- SKB_DROP_REASON_SKB_GSO_SEG
- SKB_DROP_REASON_SKB_UCOPY_FAULT
- SKB_DROP_REASON_DEV_HDR
- SKB_DROP_REASON_FULL_RING

Cc: Joao Martins <joao.m.martins@oracle.com>
Cc: Joe Jin <joe.jin@oracle.com>
Signed-off-by: default avatarDongli Zhang <dongli.zhang@oracle.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 925a2421

drivers/net/tap.c

+25 −10
Original line number Diff line number Diff line
@@ -322,6 +322,7 @@ rx_handler_result_t tap_handle_frame(struct sk_buff **pskb) 
	struct tap_dev *tap;

	struct tap_queue *q;

	netdev_features_t features = TAP_FEATURES;

	enum skb_drop_reason drop_reason;



	tap = tap_dev_get_rcu(dev);

	if (!tap)
@@ -343,12 +344,16 @@ rx_handler_result_t tap_handle_frame(struct sk_buff **pskb) 
		struct sk_buff *segs = __skb_gso_segment(skb, features, false);

		struct sk_buff *next;



		if (IS_ERR(segs))

		if (IS_ERR(segs)) {

			drop_reason = SKB_DROP_REASON_SKB_GSO_SEG;

			goto drop;

		}



		if (!segs) {

			if (ptr_ring_produce(&q->ring, skb))

			if (ptr_ring_produce(&q->ring, skb)) {

				drop_reason = SKB_DROP_REASON_FULL_RING;

				goto drop;

			}

			goto wake_up;

		}
@@ -356,8 +361,9 @@ rx_handler_result_t tap_handle_frame(struct sk_buff **pskb) 
		skb_list_walk_safe(segs, skb, next) {

			skb_mark_not_on_list(skb);

			if (ptr_ring_produce(&q->ring, skb)) {

				kfree_skb(skb);

				kfree_skb_list(next);

				drop_reason = SKB_DROP_REASON_FULL_RING;

				kfree_skb_reason(skb, drop_reason);

				kfree_skb_list_reason(next, drop_reason);

				break;

			}

		}
@@ -369,11 +375,15 @@ rx_handler_result_t tap_handle_frame(struct sk_buff **pskb) 
		 */

		if (skb->ip_summed == CHECKSUM_PARTIAL &&

		    !(features & NETIF_F_CSUM_MASK) &&

		    skb_checksum_help(skb))

		    skb_checksum_help(skb)) {

			drop_reason = SKB_DROP_REASON_SKB_CSUM;

			goto drop;

		if (ptr_ring_produce(&q->ring, skb))

		}

		if (ptr_ring_produce(&q->ring, skb)) {

			drop_reason = SKB_DROP_REASON_FULL_RING;

			goto drop;

		}

	}



wake_up:

	wake_up_interruptible_poll(sk_sleep(&q->sk), EPOLLIN | EPOLLRDNORM | EPOLLRDBAND);
@@ -383,7 +393,7 @@ rx_handler_result_t tap_handle_frame(struct sk_buff **pskb) 
	/* Count errors/drops only here, thus don't care about args. */

	if (tap->count_rx_dropped)

		tap->count_rx_dropped(tap);

	kfree_skb(skb);

	kfree_skb_reason(skb, drop_reason);

	return RX_HANDLER_CONSUMED;

}

EXPORT_SYMBOL_GPL(tap_handle_frame);
@@ -632,6 +642,7 @@ static ssize_t tap_get_user(struct tap_queue *q, void *msg_control, 
	int depth;

	bool zerocopy = false;

	size_t linear;

	enum skb_drop_reason drop_reason;



	if (q->flags & IFF_VNET_HDR) {

		vnet_hdr_len = READ_ONCE(q->vnet_hdr_sz);
@@ -696,8 +707,10 @@ static ssize_t tap_get_user(struct tap_queue *q, void *msg_control, 
	else

		err = skb_copy_datagram_from_iter(skb, 0, from, len);



	if (err)

	if (err) {

		drop_reason = SKB_DROP_REASON_SKB_UCOPY_FAULT;

		goto err_kfree;

	}



	skb_set_network_header(skb, ETH_HLEN);

	skb_reset_mac_header(skb);
@@ -706,9 +719,11 @@ static ssize_t tap_get_user(struct tap_queue *q, void *msg_control, 
	if (vnet_hdr_len) {

		err = virtio_net_hdr_to_skb(skb, &vnet_hdr,

					    tap_is_little_endian(q));

		if (err)

		if (err) {

			drop_reason = SKB_DROP_REASON_DEV_HDR;

			goto err_kfree;

		}

	}



	skb_probe_transport_header(skb);
@@ -738,7 +753,7 @@ static ssize_t tap_get_user(struct tap_queue *q, void *msg_control, 
	return total_len;



err_kfree:

	kfree_skb(skb);

	kfree_skb_reason(skb, drop_reason);



err:

	rcu_read_lock();

include/linux/skbuff.h

+13 −0
Original line number Diff line number Diff line
@@ -412,6 +412,19 @@ enum skb_drop_reason { 
					 * this means that L3 protocol is

					 * not supported

					 */

	SKB_DROP_REASON_SKB_CSUM,	/* sk_buff checksum computation

					 * error

					 */

	SKB_DROP_REASON_SKB_GSO_SEG,	/* gso segmentation error */

	SKB_DROP_REASON_SKB_UCOPY_FAULT,	/* failed to copy data from

						 * user space, e.g., via

						 * zerocopy_sg_from_iter()

						 * or skb_orphan_frags_rx()

						 */

	SKB_DROP_REASON_DEV_HDR,	/* device driver specific

					 * header/metadata is invalid

					 */

	SKB_DROP_REASON_FULL_RING,	/* ring buffer is full */

	SKB_DROP_REASON_MAX,

};

include/trace/events/skb.h

+5 −0
Original line number Diff line number Diff line
@@ -51,6 +51,11 @@ 
	EM(SKB_DROP_REASON_XDP, XDP)				\

	EM(SKB_DROP_REASON_TC_INGRESS, TC_INGRESS)		\

	EM(SKB_DROP_REASON_PTYPE_ABSENT, PTYPE_ABSENT)		\

	EM(SKB_DROP_REASON_SKB_CSUM, SKB_CSUM)			\

	EM(SKB_DROP_REASON_SKB_GSO_SEG, SKB_GSO_SEG)		\

	EM(SKB_DROP_REASON_SKB_UCOPY_FAULT, SKB_UCOPY_FAULT)	\

	EM(SKB_DROP_REASON_DEV_HDR, DEV_HDR)			\

	EM(SKB_DROP_REASON_FULL_RING, FULL_RING)		\

	EMe(SKB_DROP_REASON_MAX, MAX)



#undef EM