packet: add a generic drop reason for receive

Commit da37845fdce2 ("packet: uses kfree_skb() for errors.") switches
from consume_skb to kfree_skb to improve error handling. However, this
could bring a lot of noises when we monitor real packet drops in
kfree_skb[1], because in tpacket_rcv or packet_rcv only packet clones
can be freed, not actual packets.

Adding a generic drop reason to allow distinguish these "clone drops".

[1]: https://lore.kernel.org/netdev/CABWYdi00L+O30Q=Zah28QwZ_5RU-xcxLFUK2Zj08A8MrLk9jzg@mail.gmail.com/
Fixes: da37845fdce2 ("packet: uses kfree_skb() for errors.")
Suggested-by: Eric Dumazet <edumazet@google.com>
Suggested-by: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Signed-off-by: Yan Zhai <yan@cloudflare.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://lore.kernel.org/r/ZW4piNbx3IenYnuw@debian.debian
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/include/net/dropreason-core.h b/include/net/dropreason-core.h
index 3c70ad5..278e4c7 100644 (file)
--- a/include/net/dropreason-core.h
+++ b/include/net/dropreason-core.h
@@ -86,6 +86,7 @@
        FN(IPV6_NDISC_NS_OTHERHOST)     \
        FN(QUEUE_PURGE)                 \
        FN(TC_ERROR)                    \
+       FN(PACKET_SOCK_ERROR)           \
        FNe(MAX)
 
 /**
@@ -378,6 +379,11 @@ enum skb_drop_reason {
        SKB_DROP_REASON_QUEUE_PURGE,
        /** @SKB_DROP_REASON_TC_ERROR: generic internal tc error. */
        SKB_DROP_REASON_TC_ERROR,
+       /**
+        * @SKB_DROP_REASON_PACKET_SOCK_ERROR: generic packet socket errors
+        * after its filter matches an incoming packet.
+        */
+       SKB_DROP_REASON_PACKET_SOCK_ERROR,
        /**
         * @SKB_DROP_REASON_MAX: the maximum of core drop reasons, which
         * shouldn't be used as a real 'reason' - only for tracing code gen

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index a84e00b..f92edba 100644 (file)
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -2121,13 +2121,13 @@ static int packet_rcv_vnet(struct msghdr *msg, const struct sk_buff *skb,
 static int packet_rcv(struct sk_buff *skb, struct net_device *dev,
                      struct packet_type *pt, struct net_device *orig_dev)
 {
+       enum skb_drop_reason drop_reason = SKB_CONSUMED;
        struct sock *sk;
        struct sockaddr_ll *sll;
        struct packet_sock *po;
        u8 *skb_head = skb->data;
        int skb_len = skb->len;
        unsigned int snaplen, res;
-       bool is_drop_n_account = false;
 
        if (skb->pkt_type == PACKET_LOOPBACK)
                goto drop;
@@ -2217,9 +2217,9 @@ static int packet_rcv(struct sk_buff *skb, struct net_device *dev,
        return 0;
 
 drop_n_acct:
-       is_drop_n_account = true;
        atomic_inc(&po->tp_drops);
        atomic_inc(&sk->sk_drops);
+       drop_reason = SKB_DROP_REASON_PACKET_SOCK_ERROR;
 
 drop_n_restore:
        if (skb_head != skb->data && skb_shared(skb)) {
@@ -2227,16 +2227,14 @@ drop_n_restore:
                skb->len = skb_len;
        }
 drop:
-       if (!is_drop_n_account)
-               consume_skb(skb);
-       else
-               kfree_skb(skb);
+       kfree_skb_reason(skb, drop_reason);
        return 0;
 }
 
 static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
                       struct packet_type *pt, struct net_device *orig_dev)
 {
+       enum skb_drop_reason drop_reason = SKB_CONSUMED;
        struct sock *sk;
        struct packet_sock *po;
        struct sockaddr_ll *sll;
@@ -2250,7 +2248,6 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
        struct sk_buff *copy_skb = NULL;
        struct timespec64 ts;
        __u32 ts_status;
-       bool is_drop_n_account = false;
        unsigned int slot_id = 0;
        int vnet_hdr_sz = 0;
 
@@ -2498,19 +2495,16 @@ drop_n_restore:
                skb->len = skb_len;
        }
 drop:
-       if (!is_drop_n_account)
-               consume_skb(skb);
-       else
-               kfree_skb(skb);
+       kfree_skb_reason(skb, drop_reason);
        return 0;
 
 drop_n_account:
        spin_unlock(&sk->sk_receive_queue.lock);
        atomic_inc(&po->tp_drops);
-       is_drop_n_account = true;
+       drop_reason = SKB_DROP_REASON_PACKET_SOCK_ERROR;
 
        sk->sk_data_ready(sk);
-       kfree_skb(copy_skb);
+       kfree_skb_reason(copy_skb, drop_reason);
        goto drop_n_restore;
 }