[PATCH v4 net-next] packet: add a generic drop reason for receive

[PATCH v4 net-next] packet: add a generic drop reason for receive

[Yan Zhai]

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>
---
v3->v4: code style amend suggested by Willem de Bruijn
v2->v3: removed an unused variable
v1->v2: fixups suggested by Eric Dumazet
v3: https://lore.kernel.org/lkml/ZWomqO8m4vVcW+ro@debian.debian/
v2: https://lore.kernel.org/netdev/ZWobMUp22oTpP3FW@debian.debian/
v1: https://lore.kernel.org/netdev/ZU3EZKQ3dyLE6T8z@debian.debian/

---
 include/net/dropreason-core.h |  6 ++++++
 net/packet/af_packet.c        | 20 +++++++-------------
 2 files changed, 13 insertions(+), 13 deletions(-)

diff --git a/include/net/dropreason-core.h b/include/net/dropreason-core.h
index 3c70ad53a49c..278e4c7d465c 100644
--- 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 a84e00b5904b..f92edba4c40f 100644
--- 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 @@ static int packet_rcv(struct sk_buff *skb, struct net_device *dev,
 		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 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
 		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;
 }
 
-- 
2.30.2

Re: [PATCH v4 net-next] packet: add a generic drop reason for receive

[Eric Dumazet]

On Mon, Dec 4, 2023 at 8:33 PM Yan Zhai <yan@cloudflare.com> wrote:
>
> 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>

Re: [PATCH v4 net-next] packet: add a generic drop reason for receive

[Willem de Bruijn]

Eric Dumazet wrote:
> On Mon, Dec 4, 2023 at 8:33 PM Yan Zhai <yan@cloudflare.com> wrote:
> >
> > 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>

Re: [PATCH v4 net-next] packet: add a generic drop reason for receive

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net-next.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Mon, 4 Dec 2023 11:33:28 -0800 you wrote:
> 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".
> 
> [...]

Here is the summary with links:
  - [v4,net-next] packet: add a generic drop reason for receive
    https://git.kernel.org/netdev/net-next/c/2f57dd94bdef

You are awesome, thank you!
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