[PATCH] tcp: tcp_drop adds `SNMP` and `reason` parameter for tracing
From: Zhongya Yan
Date: Tue Sep 14 2021 - 10:36:22 EST
When we wanted to trace the use of the `tcp_drop(struct sock *sk, struct sk_buff *skb)` function, we didn't know why `tcp` was deleting `skb'. To solve this problem, I updated the function `tcp_drop(struct sock *sk, struct sk_buff *skb, int field, const char *reason)`.
This way you can understand the reason for the deletion based on the prompt message.
`field`: represents the SNMP-related value
`reason`: represents the reason why `tcp` deleted the current `skb`, and contains some hints.
Of course, if you want to know more about the reason for updating the current function, you can check: https://www.brendangregg.com/blog/2018-05-31/linux-tcpdrop.html
Signed-off-by: Zhongya Yan <yan2228598786@xxxxxxxxx>
---
include/trace/events/tcp.h | 62 ++++++++++++++++++
net/ipv4/tcp_input.c | 126 +++++++++++++++++++++++--------------
2 files changed, 142 insertions(+), 46 deletions(-)
diff --git a/include/trace/events/tcp.h b/include/trace/events/tcp.h
index 521059d8dc0a..68bbe8741ce8 100644
--- a/include/trace/events/tcp.h
+++ b/include/trace/events/tcp.h
@@ -371,6 +371,68 @@ DEFINE_EVENT(tcp_event_skb, tcp_bad_csum,
TP_ARGS(skb)
);
+TRACE_EVENT(tcp_drop,
+ TP_PROTO(struct sock *sk, struct sk_buff *skb, int field, const char *reason),
+
+ TP_ARGS(sk, skb, field, reason),
+
+ TP_STRUCT__entry(
+ __array(__u8, saddr, sizeof(struct sockaddr_in6))
+ __array(__u8, daddr, sizeof(struct sockaddr_in6))
+ __field(__u16, sport)
+ __field(__u16, dport)
+ __field(__u32, mark)
+ __field(__u16, data_len)
+ __field(__u32, snd_nxt)
+ __field(__u32, snd_una)
+ __field(__u32, snd_cwnd)
+ __field(__u32, ssthresh)
+ __field(__u32, snd_wnd)
+ __field(__u32, srtt)
+ __field(__u32, rcv_wnd)
+ __field(__u64, sock_cookie)
+ __field(int, field)
+ __string(reason, reason)
+ ),
+
+ TP_fast_assign(
+ const struct tcphdr *th = (const struct tcphdr *)skb->data;
+ const struct inet_sock *inet = inet_sk(sk);
+ const struct tcp_sock *tp = tcp_sk(sk);
+
+ memset(__entry->saddr, 0, sizeof(struct sockaddr_in6));
+ memset(__entry->daddr, 0, sizeof(struct sockaddr_in6));
+
+ TP_STORE_ADDR_PORTS(__entry, inet, sk);
+
+ __entry->sport = ntohs(inet->inet_sport);
+ __entry->dport = ntohs(inet->inet_dport);
+ __entry->mark = skb->mark;
+
+ __entry->data_len = skb->len - __tcp_hdrlen(th);
+ __entry->snd_nxt = tp->snd_nxt;
+ __entry->snd_una = tp->snd_una;
+ __entry->snd_cwnd = tp->snd_cwnd;
+ __entry->snd_wnd = tp->snd_wnd;
+ __entry->rcv_wnd = tp->rcv_wnd;
+ __entry->ssthresh = tcp_current_ssthresh(sk);
+ __entry->srtt = tp->srtt_us >> 3;
+ __entry->sock_cookie = sock_gen_cookie(sk);
+ __entry->field = field;
+
+ __assign_str(reason, reason);
+ ),
+
+ TP_printk("src=%pISpc dest=%pISpc mark=%#x data_len=%d snd_nxt=%#x snd_una=%#x \
+ snd_cwnd=%u ssthresh=%u snd_wnd=%u srtt=%u rcv_wnd=%u \
+ sock_cookie=%llx field=%d reason=%s",
+ __entry->saddr, __entry->daddr, __entry->mark,
+ __entry->data_len, __entry->snd_nxt, __entry->snd_una,
+ __entry->snd_cwnd, __entry->ssthresh, __entry->snd_wnd,
+ __entry->srtt, __entry->rcv_wnd, __entry->sock_cookie,
+ __entry->field, __get_str(reason))
+);
+
#endif /* _TRACE_TCP_H */
/* This part must be outside protection */
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 3f7bd7ae7d7a..1cebdcafb00f 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -4675,8 +4675,10 @@ static bool tcp_ooo_try_coalesce(struct sock *sk,
return res;
}
-static void tcp_drop(struct sock *sk, struct sk_buff *skb)
+static void tcp_drop(struct sock *sk, struct sk_buff *skb,
+ int field, const char *reason)
{
+ trace_tcp_drop(sk, skb, field, reason);
sk_drops_add(sk, skb);
__kfree_skb(skb);
}
@@ -4708,7 +4710,7 @@ static void tcp_ofo_queue(struct sock *sk)
rb_erase(&skb->rbnode, &tp->out_of_order_queue);
if (unlikely(!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))) {
- tcp_drop(sk, skb);
+ tcp_drop(sk, skb, LINUX_MIB_TCPOFOQUEUE, "TCP queue error");
continue;
}
@@ -4764,7 +4766,7 @@ static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb)
if (unlikely(tcp_try_rmem_schedule(sk, skb, skb->truesize))) {
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFODROP);
sk->sk_data_ready(sk);
- tcp_drop(sk, skb);
+ tcp_drop(sk, skb, LINUX_MIB_TCPOFODROP, "TCP rmem failed");
return;
}
@@ -4827,7 +4829,7 @@ static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb)
/* All the bits are present. Drop. */
NET_INC_STATS(sock_net(sk),
LINUX_MIB_TCPOFOMERGE);
- tcp_drop(sk, skb);
+ tcp_drop(sk, skb, LINUX_MIB_TCPOFOMERGE, "TCP bits are present");
skb = NULL;
tcp_dsack_set(sk, seq, end_seq);
goto add_sack;
@@ -4846,7 +4848,9 @@ static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb)
TCP_SKB_CB(skb1)->end_seq);
NET_INC_STATS(sock_net(sk),
LINUX_MIB_TCPOFOMERGE);
- tcp_drop(sk, skb1);
+ tcp_drop(sk, skb1, LINUX_MIB_TCPOFOMERGE,
+ "TCP replace(skb.seq eq skb1.seq)");
+
goto merge_right;
}
} else if (tcp_ooo_try_coalesce(sk, skb1,
@@ -4874,7 +4878,7 @@ static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb)
tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
TCP_SKB_CB(skb1)->end_seq);
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFOMERGE);
- tcp_drop(sk, skb1);
+ tcp_drop(sk, skb1, LINUX_MIB_TCPOFOMERGE, "TCP useless other segments");
}
/* If there is no skb after us, we are the last_skb ! */
if (!skb1)
@@ -5010,7 +5014,8 @@ static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
else if (tcp_try_rmem_schedule(sk, skb, skb->truesize)) {
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVQDROP);
sk->sk_data_ready(sk);
- goto drop;
+ tcp_drop(sk, skb, LINUX_MIB_TCPRCVQDROP, "TCP rmem failed");
+ goto end;
}
eaten = tcp_queue_rcv(sk, skb, &fragstolen);
@@ -5050,8 +5055,8 @@ static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
out_of_window:
tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS);
inet_csk_schedule_ack(sk);
-drop:
- tcp_drop(sk, skb);
+ tcp_drop(sk, skb, LINUX_MIB_TCPZEROWINDOWDROP, "TCP out of order or zero window");
+end:
return;
}
@@ -5308,7 +5313,7 @@ static bool tcp_prune_ofo_queue(struct sock *sk)
prev = rb_prev(node);
rb_erase(node, &tp->out_of_order_queue);
goal -= rb_to_skb(node)->truesize;
- tcp_drop(sk, rb_to_skb(node));
+ tcp_drop(sk, rb_to_skb(node), LINUX_MIB_OFOPRUNED, "TCP drop out-of-order queue");
if (!prev || goal <= 0) {
sk_mem_reclaim(sk);
if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf &&
@@ -5643,7 +5648,8 @@ static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
LINUX_MIB_TCPACKSKIPPEDPAWS,
&tp->last_oow_ack_time))
tcp_send_dupack(sk, skb);
- goto discard;
+ tcp_drop(sk, skb, LINUX_MIB_PAWSESTABREJECTED, "TCP PAWS seq first");
+ goto end;
}
/* Reset is accepted even if it did not pass PAWS. */
}
@@ -5666,7 +5672,8 @@ static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
} else if (tcp_reset_check(sk, skb)) {
tcp_reset(sk, skb);
}
- goto discard;
+ tcp_drop(sk, skb, LINUX_MIB_PAWSESTABREJECTED, "TCP check sequence number");
+ goto end;
}
/* Step 2: check RST bit */
@@ -5711,7 +5718,8 @@ static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
tcp_fastopen_active_disable(sk);
tcp_send_challenge_ack(sk, skb);
}
- goto discard;
+ tcp_drop(sk, skb, LINUX_MIB_TCPCHALLENGEACK, "TCP check RST bit ");
+ goto end;
}
/* step 3: check security and precedence [ignored] */
@@ -5725,15 +5733,15 @@ static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNCHALLENGE);
tcp_send_challenge_ack(sk, skb);
- goto discard;
+ tcp_drop(sk, skb, LINUX_MIB_TCPSYNCHALLENGE, "TCP check for a SYN");
+ goto end;
}
bpf_skops_parse_hdr(sk, skb);
return true;
-discard:
- tcp_drop(sk, skb);
+end:
return false;
}
@@ -5851,7 +5859,8 @@ void tcp_rcv_established(struct sock *sk, struct sk_buff *skb)
return;
} else { /* Header too small */
TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
- goto discard;
+ tcp_drop(sk, skb, TCP_MIB_INERRS, "TCP header too small");
+ goto end;
}
} else {
int eaten = 0;
@@ -5905,8 +5914,10 @@ void tcp_rcv_established(struct sock *sk, struct sk_buff *skb)
if (len < (th->doff << 2) || tcp_checksum_complete(skb))
goto csum_error;
- if (!th->ack && !th->rst && !th->syn)
- goto discard;
+ if (!th->ack && !th->rst && !th->syn) {
+ tcp_drop(sk, skb, LINUX_MIB_TCPSLOWSTARTRETRANS, "TCP state not in ack|rst|syn");
+ goto end;
+ }
/*
* Standard slow path.
@@ -5916,8 +5927,10 @@ void tcp_rcv_established(struct sock *sk, struct sk_buff *skb)
return;
step5:
- if (tcp_ack(sk, skb, FLAG_SLOWPATH | FLAG_UPDATE_TS_RECENT) < 0)
- goto discard;
+ if (tcp_ack(sk, skb, FLAG_SLOWPATH | FLAG_UPDATE_TS_RECENT) < 0) {
+ tcp_drop(sk, skb, LINUX_MIB_TCPSACKDISCARD, "TCP ack have not sent yet");
+ goto end;
+ }
tcp_rcv_rtt_measure_ts(sk, skb);
@@ -5935,9 +5948,10 @@ void tcp_rcv_established(struct sock *sk, struct sk_buff *skb)
trace_tcp_bad_csum(skb);
TCP_INC_STATS(sock_net(sk), TCP_MIB_CSUMERRORS);
TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
+ tcp_drop(sk, skb, TCP_MIB_CSUMERRORS, "TCP csum error");
-discard:
- tcp_drop(sk, skb);
+end:
+ return;
}
EXPORT_SYMBOL(tcp_rcv_established);
@@ -6137,7 +6151,8 @@ static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
if (th->rst) {
tcp_reset(sk, skb);
- goto discard;
+ tcp_drop(sk, skb, LINUX_MIB_NUM, "TCP reset");
+ goto end;
}
/* rfc793:
@@ -6226,9 +6241,9 @@ static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS);
inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
TCP_DELACK_MAX, TCP_RTO_MAX);
+ tcp_drop(sk, skb, LINUX_MIB_TCPFASTOPENACTIVE, "TCP fast open ack error");
-discard:
- tcp_drop(sk, skb);
+end:
return 0;
} else {
tcp_send_ack(sk);
@@ -6301,7 +6316,8 @@ static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
*/
return -1;
#else
- goto discard;
+ tcp_drop(sk, skb, LINUX_MIB_SYNCOOKIESRECV, "TCP syn received error");
+ goto end;
#endif
}
/* "fifth, if neither of the SYN or RST bits is set then
@@ -6311,7 +6327,8 @@ static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
discard_and_undo:
tcp_clear_options(&tp->rx_opt);
tp->rx_opt.mss_clamp = saved_clamp;
- goto discard;
+ tcp_drop(sk, skb, LINUX_MIB_TCPSACKDISCARD, "TCP not neither of SYN or RST");
+ goto end;
reset_and_undo:
tcp_clear_options(&tp->rx_opt);
@@ -6369,18 +6386,23 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
switch (sk->sk_state) {
case TCP_CLOSE:
- goto discard;
+ tcp_drop(sk, skb, LINUX_MIB_TCPABORTONCLOSE, "TCP close");
+ goto end;
case TCP_LISTEN:
if (th->ack)
return 1;
- if (th->rst)
- goto discard;
+ if (th->rst) {
+ tcp_drop(sk, skb, LINUX_MIB_LISTENDROPS, "TCP rst");
+ goto end;
+ }
if (th->syn) {
- if (th->fin)
- goto discard;
+ if (th->fin) {
+ tcp_drop(sk, skb, LINUX_MIB_LISTENDROPS, "TCP fin");
+ goto end;
+ }
/* It is possible that we process SYN packets from backlog,
* so we need to make sure to disable BH and RCU right there.
*/
@@ -6395,7 +6417,8 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
consume_skb(skb);
return 0;
}
- goto discard;
+ tcp_drop(sk, skb, LINUX_MIB_LISTENDROPS, "TCP syn");
+ goto end;
case TCP_SYN_SENT:
tp->rx_opt.saw_tstamp = 0;
@@ -6421,12 +6444,16 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&
sk->sk_state != TCP_FIN_WAIT1);
- if (!tcp_check_req(sk, skb, req, true, &req_stolen))
- goto discard;
+ if (!tcp_check_req(sk, skb, req, true, &req_stolen)) {
+ tcp_drop(sk, skb, LINUX_MIB_LISTENDROPS, "TCP check req error");
+ goto end;
+ }
}
- if (!th->ack && !th->rst && !th->syn)
- goto discard;
+ if (!th->ack && !th->rst && !th->syn) {
+ tcp_drop(sk, skb, LINUX_MIB_LISTENDROPS, "TCP not ack|rst|syn");
+ goto end;
+ }
if (!tcp_validate_incoming(sk, skb, th, 0))
return 0;
@@ -6440,7 +6467,8 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
if (sk->sk_state == TCP_SYN_RECV)
return 1; /* send one RST */
tcp_send_challenge_ack(sk, skb);
- goto discard;
+ tcp_drop(sk, skb, LINUX_MIB_TCPCHALLENGEACK, "TCP check ack failed");
+ goto end;
}
switch (sk->sk_state) {
case TCP_SYN_RECV:
@@ -6533,7 +6561,8 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
inet_csk_reset_keepalive_timer(sk, tmo);
} else {
tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
- goto discard;
+ tcp_drop(sk, skb, LINUX_MIB_TCPABORTONDATA, "TCP fin wait2");
+ goto end;
}
break;
}
@@ -6541,7 +6570,8 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
case TCP_CLOSING:
if (tp->snd_una == tp->write_seq) {
tcp_time_wait(sk, TCP_TIME_WAIT, 0);
- goto discard;
+ tcp_drop(sk, skb, LINUX_MIB_TIMEWAITED, "TCP time wait");
+ goto end;
}
break;
@@ -6549,7 +6579,8 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
if (tp->snd_una == tp->write_seq) {
tcp_update_metrics(sk);
tcp_done(sk);
- goto discard;
+ tcp_drop(sk, skb, LINUX_MIB_TCPPUREACKS, "TCP last ack");
+ goto end;
}
break;
}
@@ -6566,8 +6597,10 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
/* If a subflow has been reset, the packet should not
* continue to be processed, drop the packet.
*/
- if (sk_is_mptcp(sk) && !mptcp_incoming_options(sk, skb))
- goto discard;
+ if (sk_is_mptcp(sk) && !mptcp_incoming_options(sk, skb)) {
+ tcp_drop(sk, skb, LINUX_MIB_TCPPUREACKS, "TCP subflow been reset");
+ goto end;
+ }
break;
}
fallthrough;
@@ -6599,9 +6632,10 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
}
if (!queued) {
-discard:
- tcp_drop(sk, skb);
+ tcp_drop(sk, skb, LINUX_MIB_TCPOFOQUEUE, "TCP rcv synsent state process");
}
+
+end:
return 0;
}
EXPORT_SYMBOL(tcp_rcv_state_process);
--
2.25.1