On 2/18/22 1:31 AM, menglong8.dong@xxxxxxxxx wrote:
> From: Menglong Dong <imagedong@xxxxxxxxxxx>
>
> In the commit c504e5c2f964 ("net: skb: introduce kfree_skb_reason()"),
> we added the support of reporting the reasons of skb drops to kfree_skb
> tracepoint. And in this series patches, reasons for skb drops are added
> to TCP layer (both TCPv4 and TCPv6 are considered).
> Following functions are processed:
>
> tcp_v4_rcv()
> tcp_v6_rcv()
> tcp_v4_inbound_md5_hash()
> tcp_v6_inbound_md5_hash()
> tcp_add_backlog()
> tcp_v4_do_rcv()
> tcp_v6_do_rcv()
> tcp_rcv_established()
> tcp_data_queue()
> tcp_data_queue_ofo()
>
> The functions we handled are mostly for packet ingress, as skb drops
> hardly happens in the egress path of TCP layer. However, it's a little
> complex for TCP state processing, as I find that it's hard to report skb
> drop reasons to where it is freed. For example, when skb is dropped in
> tcp_rcv_state_process(), the reason can be caused by the call of
> tcp_v4_conn_request(), and it's hard to return a drop reason from
> tcp_v4_conn_request(). So such cases are skipped for this moment.
>
> Following new drop reasons are introduced (what they mean can be see
> in the document for them):
>
> /* SKB_DROP_REASON_TCP_MD5* corresponding to LINUX_MIB_TCPMD5* */
> SKB_DROP_REASON_TCP_MD5NOTFOUND
> SKB_DROP_REASON_TCP_MD5UNEXPECTED
> SKB_DROP_REASON_TCP_MD5FAILURE
> SKB_DROP_REASON_SOCKET_BACKLOG
> SKB_DROP_REASON_TCP_FLAGS
> SKB_DROP_REASON_TCP_ZEROWINDOW
> SKB_DROP_REASON_TCP_OLD_DATA
> SKB_DROP_REASON_TCP_OVERWINDOW
> /* corresponding to LINUX_MIB_TCPOFOMERGE */
> SKB_DROP_REASON_TCP_OFOMERGE
>
> Here is a example to get TCP packet drop reasons from ftrace:
>
> $ echo 1 > /sys/kernel/debug/tracing/events/skb/kfree_skb/enable
> $ cat /sys/kernel/debug/tracing/trace
> $ <idle>-0 [036] ..s1. 647.428165: kfree_skb: skbaddr=000000004d037db6 protocol=2048 location=0000000074cd1243 reason: NO_SOCKET
> $ <idle>-0 [020] ..s2. 639.676674: kfree_skb: skbaddr=00000000bcbfa42d protocol=2048 location=00000000bfe89d35 reason: PROTO_MEM
>
> From the reason 'PROTO_MEM' we can know that the skb is dropped because
> the memory configured in net.ipv4.tcp_mem is up to the limition.
>
> Changes since v1:
> - enrich the document for this series patches in the cover letter,
> as Eric suggested
> - fix compile warning report by Jakub in the 6th patch
> - let NO_SOCKET trump the XFRM failure in the 2th and 3th patches
>
> Menglong Dong (9):
> net: tcp: introduce tcp_drop_reason()
> net: tcp: add skb drop reasons to tcp_v4_rcv()
> net: tcp: use kfree_skb_reason() for tcp_v6_rcv()
> net: tcp: add skb drop reasons to tcp_v{4,6}_inbound_md5_hash()
> net: tcp: add skb drop reasons to tcp_add_backlog()
> net: tcp: use kfree_skb_reason() for tcp_v{4,6}_do_rcv()
> net: tcp: use tcp_drop_reason() for tcp_rcv_established()
> net: tcp: use tcp_drop_reason() for tcp_data_queue()
> net: tcp: use tcp_drop_reason() for tcp_data_queue_ofo()
>
> include/linux/skbuff.h | 34 ++++++++++++++++++++++++++++++
> include/net/tcp.h | 3 ++-
> include/trace/events/skb.h | 10 +++++++++
> net/ipv4/tcp_input.c | 42 +++++++++++++++++++++++++++++---------
> net/ipv4/tcp_ipv4.c | 32 +++++++++++++++++++++--------
> net/ipv6/tcp_ipv6.c | 39 +++++++++++++++++++++++++++--------
> 6 files changed, 132 insertions(+), 28 deletions(-)
>
LGTM. for the set:
Reviewed-by: David Ahern <dsahern@xxxxxxxxxx>
