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net: tap: track dropped skb via kfree_skb_reason()

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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: Dongli Zhang <dongli.zhang@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Dongli Zhang 2022-03-04 06:55:05 -08:00 committed by David S. Miller
parent 925a24213b
commit 736f16de75
3 changed files with 43 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

35
drivers/net/tap.c
View File

@ -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;
}
}
@ -369,10 +375,14 @@ 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:
@ -383,7 +393,7 @@ drop:
/* 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);
@ -706,8 +719,10 @@ 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();

13
include/linux/skbuff.h
View File

@ -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,
};

5
include/trace/events/skb.h
View File

@ -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