[PATCH net-next v5 2/4] net: tap: track dropped skb via kfree_skb_reason()
From: Dongli Zhang
Date: Fri Mar 04 2022 - 01:34:34 EST
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@xxxxxxxxxx>
Cc: Joe Jin <joe.jin@xxxxxxxxxx>
Signed-off-by: Dongli Zhang <dongli.zhang@xxxxxxxxxx>
---
Changed since v1:
- revise the reason name
Changed since v2:
- declare drop_reason as type "enum skb_drop_reason"
- handle the drop in skb_list_walk_safe() case
Changed since v4:
- add 'computation' to SKB_CSUM comment
- change COPY_DATA to UCOPY_FAULT
- add 'metadata' to DEV_HDR comment
drivers/net/tap.c | 35 +++++++++++++++++++++++++----------
include/linux/skbuff.h | 13 +++++++++++++
include/trace/events/skb.h | 5 +++++
3 files changed, 43 insertions(+), 10 deletions(-)
diff --git a/drivers/net/tap.c b/drivers/net/tap.c
index ba2ef5437e16..c3d42062559d 100644
--- a/drivers/net/tap.c
+++ b/drivers/net/tap.c
@@ -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 @@ 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);
@@ -706,8 +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();
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index bb00f86791e0..e5d5371a543b 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -394,6 +394,19 @@ enum skb_drop_reason {
* entry is full
*/
SKB_DROP_REASON_NEIGH_DEAD, /* neigh entry is dead */
+ 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,
};
diff --git a/include/trace/events/skb.h b/include/trace/events/skb.h
index 1977f301260d..9d91ec9755b8 100644
--- a/include/trace/events/skb.h
+++ b/include/trace/events/skb.h
@@ -45,6 +45,11 @@
EM(SKB_DROP_REASON_NEIGH_FAILED, NEIGH_FAILED) \
EM(SKB_DROP_REASON_NEIGH_QUEUEFULL, NEIGH_QUEUEFULL) \
EM(SKB_DROP_REASON_NEIGH_DEAD, NEIGH_DEAD) \
+ 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
--
2.17.1