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: Dongli Zhang <dongli.zhang@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/tap.c b/drivers/net/tap.c
index ba2ef54..c3d4206 100644 (file)
--- 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 @@ 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();

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 2be2631..67cfff4 100644 (file)
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -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,
 };
 

diff --git a/include/trace/events/skb.h b/include/trace/events/skb.h
index c0769d9..240e7e7 100644 (file)
--- a/include/trace/events/skb.h
+++ b/include/trace/events/skb.h
@@ -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