Menglong Dong says: ==================== net: add skb drop reasons to TCP packet receive 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 v2: - remove the 'inline' of tcp_drop() in the 1th patch, as Jakub suggested 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 ==================== Signed-off-by: David S. Miller <davem@davemloft.net>