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Date:   Sat, 29 Oct 2022 21:09:48 +0800
Subject: [PATCH net-next 0/9] net: tcp: add skb drop reasons to tcp state process

From: Menglong Dong <>

For now, the skb drop reasons have not fully be supported by TCP
protocol on the code path of TCP connection state change. The function
call chain is a little complex, which makes it hard to get the reason
that why skb is dropped.

However, I have a idea now: store the drop reason in the tcp_skb_cb,
which means that we need to add a 'drop_reason' field to the struct
tcp_skb_cb. Luckily, this struct still has 4 bytes spare space for this

In this way, we need only to initialize to 'TCP_SKB_CB(skb)->drop_reason'
to SKB_DROP_REASON_NOT_SPECIFIED in tcp_v4_rcv()/tcp_v6_rcv(). When the
skb needs to be dropped, the value of this field should be the drop
reason or SKB_DROP_REASON_NOT_SPECIFIED. Meanwhile, the value also can be
SKB_NOT_DROPPED_YET. On such case, try_kfree_skb(), which we add in the
1th patch, should be called.

Hi, Eric, do you like it? In this way, we almost don't need to change the
exist code, and won't mess the code up.

In this series, the skb drop reasons are added following functions:


And following new drop reasons are added:


Menglong Dong (9):
  net: skb: introduce try_kfree_skb()
  net: tcp: add 'drop_reason' field to struct tcp_skb_cb
  net: tcp: use the drop reasons stored in tcp_skb_cb
  net: tcp: store drop reasons in tcp_rcv_synsent_state_process()
  net: tcp: store drop reasons in tcp_timewait_state_process()
  net: tcp: store drop reasons in tcp_conn_request()
  net: tcp: store drop reasons in tcp_rcv_state_process()
  net: tcp: store drop reasons in route_req
  net: tcp: use LINUX_MIB_TCPABORTONLINGER in tcp_rcv_state_process()

 include/linux/skbuff.h   |  9 +++++++++
 include/net/dropreason.h | 43 ++++++++++++++++++++++++++++++++++++++++
 include/net/tcp.h        |  3 +++
 net/ipv4/tcp_input.c     | 29 ++++++++++++++++++++++-----
 net/ipv4/tcp_ipv4.c      | 26 ++++++++++++++++++++----
 net/ipv4/tcp_minisocks.c | 15 ++++++++++++--
 net/ipv6/tcp_ipv6.c      | 31 +++++++++++++++++++++++------
 7 files changed, 139 insertions(+), 17 deletions(-)


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