Merge branch 'net-extend-drop-reasons'

Johannes Berg says:

====================
net: extend drop reasons

Here's v4 of the extended drop reasons, with fixes to kernel-doc
and checkpatch.
====================

Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

include/linux/netdevice.h

···
 #include <linux/rbtree.h>
 #include <net/net_trackers.h>
 #include <net/net_debug.h>
-#include <net/dropreason.h>
+#include <net/dropreason-core.h>
 
 struct netpoll_info;
 struct device;

include/linux/skbuff.h

···
 #include <linux/netfilter/nf_conntrack_common.h>
 #endif
 #include <net/net_debug.h>
-#include <net/dropreason.h>
+#include <net/dropreason-core.h>
 
 /**
  * DOC: skb checksums

include/net/dropreason-core.h

···
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#ifndef _LINUX_DROPREASON_CORE_H
+#define _LINUX_DROPREASON_CORE_H
+
+#define DEFINE_DROP_REASON(FN, FNe)	\
+	FN(NOT_SPECIFIED)		\
+	FN(NO_SOCKET)			\
+	FN(PKT_TOO_SMALL)		\
+	FN(TCP_CSUM)			\
+	FN(SOCKET_FILTER)		\
+	FN(UDP_CSUM)			\
+	FN(NETFILTER_DROP)		\
+	FN(OTHERHOST)			\
+	FN(IP_CSUM)			\
+	FN(IP_INHDR)			\
+	FN(IP_RPFILTER)			\
+	FN(UNICAST_IN_L2_MULTICAST)	\
+	FN(XFRM_POLICY)			\
+	FN(IP_NOPROTO)			\
+	FN(SOCKET_RCVBUFF)		\
+	FN(PROTO_MEM)			\
+	FN(TCP_MD5NOTFOUND)		\
+	FN(TCP_MD5UNEXPECTED)		\
+	FN(TCP_MD5FAILURE)		\
+	FN(SOCKET_BACKLOG)		\
+	FN(TCP_FLAGS)			\
+	FN(TCP_ZEROWINDOW)		\
+	FN(TCP_OLD_DATA)		\
+	FN(TCP_OVERWINDOW)		\
+	FN(TCP_OFOMERGE)		\
+	FN(TCP_RFC7323_PAWS)		\
+	FN(TCP_INVALID_SEQUENCE)	\
+	FN(TCP_RESET)			\
+	FN(TCP_INVALID_SYN)		\
+	FN(TCP_CLOSE)			\
+	FN(TCP_FASTOPEN)		\
+	FN(TCP_OLD_ACK)			\
+	FN(TCP_TOO_OLD_ACK)		\
+	FN(TCP_ACK_UNSENT_DATA)		\
+	FN(TCP_OFO_QUEUE_PRUNE)		\
+	FN(TCP_OFO_DROP)		\
+	FN(IP_OUTNOROUTES)		\
+	FN(BPF_CGROUP_EGRESS)		\
+	FN(IPV6DISABLED)		\
+	FN(NEIGH_CREATEFAIL)		\
+	FN(NEIGH_FAILED)		\
+	FN(NEIGH_QUEUEFULL)		\
+	FN(NEIGH_DEAD)			\
+	FN(TC_EGRESS)			\
+	FN(QDISC_DROP)			\
+	FN(CPU_BACKLOG)			\
+	FN(XDP)				\
+	FN(TC_INGRESS)			\
+	FN(UNHANDLED_PROTO)		\
+	FN(SKB_CSUM)			\
+	FN(SKB_GSO_SEG)			\
+	FN(SKB_UCOPY_FAULT)		\
+	FN(DEV_HDR)			\
+	FN(DEV_READY)			\
+	FN(FULL_RING)			\
+	FN(NOMEM)			\
+	FN(HDR_TRUNC)			\
+	FN(TAP_FILTER)			\
+	FN(TAP_TXFILTER)		\
+	FN(ICMP_CSUM)			\
+	FN(INVALID_PROTO)		\
+	FN(IP_INADDRERRORS)		\
+	FN(IP_INNOROUTES)		\
+	FN(PKT_TOO_BIG)			\
+	FN(DUP_FRAG)			\
+	FN(FRAG_REASM_TIMEOUT)		\
+	FN(FRAG_TOO_FAR)		\
+	FN(TCP_MINTTL)			\
+	FN(IPV6_BAD_EXTHDR)		\
+	FN(IPV6_NDISC_FRAG)		\
+	FN(IPV6_NDISC_HOP_LIMIT)	\
+	FN(IPV6_NDISC_BAD_CODE)		\
+	FN(IPV6_NDISC_BAD_OPTIONS)	\
+	FN(IPV6_NDISC_NS_OTHERHOST)	\
+	FNe(MAX)
+
+/**
+ * enum skb_drop_reason - the reasons of skb drops
+ *
+ * The reason of skb drop, which is used in kfree_skb_reason().
+ */
+enum skb_drop_reason {
+	/**
+	 * @SKB_NOT_DROPPED_YET: skb is not dropped yet (used for no-drop case)
+	 */
+	SKB_NOT_DROPPED_YET = 0,
+	/** @SKB_CONSUMED: packet has been consumed */
+	SKB_CONSUMED,
+	/** @SKB_DROP_REASON_NOT_SPECIFIED: drop reason is not specified */
+	SKB_DROP_REASON_NOT_SPECIFIED,
+	/** @SKB_DROP_REASON_NO_SOCKET: socket not found */
+	SKB_DROP_REASON_NO_SOCKET,
+	/** @SKB_DROP_REASON_PKT_TOO_SMALL: packet size is too small */
+	SKB_DROP_REASON_PKT_TOO_SMALL,
+	/** @SKB_DROP_REASON_TCP_CSUM: TCP checksum error */
+	SKB_DROP_REASON_TCP_CSUM,
+	/** @SKB_DROP_REASON_SOCKET_FILTER: dropped by socket filter */
+	SKB_DROP_REASON_SOCKET_FILTER,
+	/** @SKB_DROP_REASON_UDP_CSUM: UDP checksum error */
+	SKB_DROP_REASON_UDP_CSUM,
+	/** @SKB_DROP_REASON_NETFILTER_DROP: dropped by netfilter */
+	SKB_DROP_REASON_NETFILTER_DROP,
+	/**
+	 * @SKB_DROP_REASON_OTHERHOST: packet don't belong to current host
+	 * (interface is in promisc mode)
+	 */
+	SKB_DROP_REASON_OTHERHOST,
+	/** @SKB_DROP_REASON_IP_CSUM: IP checksum error */
+	SKB_DROP_REASON_IP_CSUM,
+	/**
+	 * @SKB_DROP_REASON_IP_INHDR: there is something wrong with IP header (see
+	 * IPSTATS_MIB_INHDRERRORS)
+	 */
+	SKB_DROP_REASON_IP_INHDR,
+	/**
+	 * @SKB_DROP_REASON_IP_RPFILTER: IP rpfilter validate failed. see the
+	 * document for rp_filter in ip-sysctl.rst for more information
+	 */
+	SKB_DROP_REASON_IP_RPFILTER,
+	/**
+	 * @SKB_DROP_REASON_UNICAST_IN_L2_MULTICAST: destination address of L2 is
+	 * multicast, but L3 is unicast.
+	 */
+	SKB_DROP_REASON_UNICAST_IN_L2_MULTICAST,
+	/** @SKB_DROP_REASON_XFRM_POLICY: xfrm policy check failed */
+	SKB_DROP_REASON_XFRM_POLICY,
+	/** @SKB_DROP_REASON_IP_NOPROTO: no support for IP protocol */
+	SKB_DROP_REASON_IP_NOPROTO,
+	/** @SKB_DROP_REASON_SOCKET_RCVBUFF: socket receive buff is full */
+	SKB_DROP_REASON_SOCKET_RCVBUFF,
+	/**
+	 * @SKB_DROP_REASON_PROTO_MEM: proto memory limition, such as udp packet
+	 * drop out of udp_memory_allocated.
+	 */
+	SKB_DROP_REASON_PROTO_MEM,
+	/**
+	 * @SKB_DROP_REASON_TCP_MD5NOTFOUND: no MD5 hash and one expected,
+	 * corresponding to LINUX_MIB_TCPMD5NOTFOUND
+	 */
+	SKB_DROP_REASON_TCP_MD5NOTFOUND,
+	/**
+	 * @SKB_DROP_REASON_TCP_MD5UNEXPECTED: MD5 hash and we're not expecting
+	 * one, corresponding to LINUX_MIB_TCPMD5UNEXPECTED
+	 */
+	SKB_DROP_REASON_TCP_MD5UNEXPECTED,
+	/**
+	 * @SKB_DROP_REASON_TCP_MD5FAILURE: MD5 hash and its wrong, corresponding
+	 * to LINUX_MIB_TCPMD5FAILURE
+	 */
+	SKB_DROP_REASON_TCP_MD5FAILURE,
+	/**
+	 * @SKB_DROP_REASON_SOCKET_BACKLOG: failed to add skb to socket backlog (
+	 * see LINUX_MIB_TCPBACKLOGDROP)
+	 */
+	SKB_DROP_REASON_SOCKET_BACKLOG,
+	/** @SKB_DROP_REASON_TCP_FLAGS: TCP flags invalid */
+	SKB_DROP_REASON_TCP_FLAGS,
+	/**
+	 * @SKB_DROP_REASON_TCP_ZEROWINDOW: TCP receive window size is zero,
+	 * see LINUX_MIB_TCPZEROWINDOWDROP
+	 */
+	SKB_DROP_REASON_TCP_ZEROWINDOW,
+	/**
+	 * @SKB_DROP_REASON_TCP_OLD_DATA: the TCP data reveived is already
+	 * received before (spurious retrans may happened), see
+	 * LINUX_MIB_DELAYEDACKLOST
+	 */
+	SKB_DROP_REASON_TCP_OLD_DATA,
+	/**
+	 * @SKB_DROP_REASON_TCP_OVERWINDOW: the TCP data is out of window,
+	 * the seq of the first byte exceed the right edges of receive
+	 * window
+	 */
+	SKB_DROP_REASON_TCP_OVERWINDOW,
+	/**
+	 * @SKB_DROP_REASON_TCP_OFOMERGE: the data of skb is already in the ofo
+	 * queue, corresponding to LINUX_MIB_TCPOFOMERGE
+	 */
+	SKB_DROP_REASON_TCP_OFOMERGE,
+	/**
+	 * @SKB_DROP_REASON_TCP_RFC7323_PAWS: PAWS check, corresponding to
+	 * LINUX_MIB_PAWSESTABREJECTED
+	 */
+	SKB_DROP_REASON_TCP_RFC7323_PAWS,
+	/** @SKB_DROP_REASON_TCP_INVALID_SEQUENCE: Not acceptable SEQ field */
+	SKB_DROP_REASON_TCP_INVALID_SEQUENCE,
+	/** @SKB_DROP_REASON_TCP_RESET: Invalid RST packet */
+	SKB_DROP_REASON_TCP_RESET,
+	/**
+	 * @SKB_DROP_REASON_TCP_INVALID_SYN: Incoming packet has unexpected
+	 * SYN flag
+	 */
+	SKB_DROP_REASON_TCP_INVALID_SYN,
+	/** @SKB_DROP_REASON_TCP_CLOSE: TCP socket in CLOSE state */
+	SKB_DROP_REASON_TCP_CLOSE,
+	/** @SKB_DROP_REASON_TCP_FASTOPEN: dropped by FASTOPEN request socket */
+	SKB_DROP_REASON_TCP_FASTOPEN,
+	/** @SKB_DROP_REASON_TCP_OLD_ACK: TCP ACK is old, but in window */
+	SKB_DROP_REASON_TCP_OLD_ACK,
+	/** @SKB_DROP_REASON_TCP_TOO_OLD_ACK: TCP ACK is too old */
+	SKB_DROP_REASON_TCP_TOO_OLD_ACK,
+	/**
+	 * @SKB_DROP_REASON_TCP_ACK_UNSENT_DATA: TCP ACK for data we haven't
+	 * sent yet
+	 */
+	SKB_DROP_REASON_TCP_ACK_UNSENT_DATA,
+	/** @SKB_DROP_REASON_TCP_OFO_QUEUE_PRUNE: pruned from TCP OFO queue */
+	SKB_DROP_REASON_TCP_OFO_QUEUE_PRUNE,
+	/** @SKB_DROP_REASON_TCP_OFO_DROP: data already in receive queue */
+	SKB_DROP_REASON_TCP_OFO_DROP,
+	/** @SKB_DROP_REASON_IP_OUTNOROUTES: route lookup failed */
+	SKB_DROP_REASON_IP_OUTNOROUTES,
+	/**
+	 * @SKB_DROP_REASON_BPF_CGROUP_EGRESS: dropped by BPF_PROG_TYPE_CGROUP_SKB
+	 * eBPF program
+	 */
+	SKB_DROP_REASON_BPF_CGROUP_EGRESS,
+	/** @SKB_DROP_REASON_IPV6DISABLED: IPv6 is disabled on the device */
+	SKB_DROP_REASON_IPV6DISABLED,
+	/** @SKB_DROP_REASON_NEIGH_CREATEFAIL: failed to create neigh entry */
+	SKB_DROP_REASON_NEIGH_CREATEFAIL,
+	/** @SKB_DROP_REASON_NEIGH_FAILED: neigh entry in failed state */
+	SKB_DROP_REASON_NEIGH_FAILED,
+	/** @SKB_DROP_REASON_NEIGH_QUEUEFULL: arp_queue for neigh entry is full */
+	SKB_DROP_REASON_NEIGH_QUEUEFULL,
+	/** @SKB_DROP_REASON_NEIGH_DEAD: neigh entry is dead */
+	SKB_DROP_REASON_NEIGH_DEAD,
+	/** @SKB_DROP_REASON_TC_EGRESS: dropped in TC egress HOOK */
+	SKB_DROP_REASON_TC_EGRESS,
+	/**
+	 * @SKB_DROP_REASON_QDISC_DROP: dropped by qdisc when packet outputting (
+	 * failed to enqueue to current qdisc)
+	 */
+	SKB_DROP_REASON_QDISC_DROP,
+	/**
+	 * @SKB_DROP_REASON_CPU_BACKLOG: failed to enqueue the skb to the per CPU
+	 * backlog queue. This can be caused by backlog queue full (see
+	 * netdev_max_backlog in net.rst) or RPS flow limit
+	 */
+	SKB_DROP_REASON_CPU_BACKLOG,
+	/** @SKB_DROP_REASON_XDP: dropped by XDP in input path */
+	SKB_DROP_REASON_XDP,
+	/** @SKB_DROP_REASON_TC_INGRESS: dropped in TC ingress HOOK */
+	SKB_DROP_REASON_TC_INGRESS,
+	/** @SKB_DROP_REASON_UNHANDLED_PROTO: protocol not implemented or not supported */
+	SKB_DROP_REASON_UNHANDLED_PROTO,
+	/** @SKB_DROP_REASON_SKB_CSUM: sk_buff checksum computation error */
+	SKB_DROP_REASON_SKB_CSUM,
+	/** @SKB_DROP_REASON_SKB_GSO_SEG: gso segmentation error */
+	SKB_DROP_REASON_SKB_GSO_SEG,
+	/**
+	 * @SKB_DROP_REASON_SKB_UCOPY_FAULT: failed to copy data from user space,
+	 * e.g., via zerocopy_sg_from_iter() or skb_orphan_frags_rx()
+	 */
+	SKB_DROP_REASON_SKB_UCOPY_FAULT,
+	/** @SKB_DROP_REASON_DEV_HDR: device driver specific header/metadata is invalid */
+	SKB_DROP_REASON_DEV_HDR,
+	/**
+	 * @SKB_DROP_REASON_DEV_READY: the device is not ready to xmit/recv due to
+	 * any of its data structure that is not up/ready/initialized,
+	 * e.g., the IFF_UP is not set, or driver specific tun->tfiles[txq]
+	 * is not initialized
+	 */
+	SKB_DROP_REASON_DEV_READY,
+	/** @SKB_DROP_REASON_FULL_RING: ring buffer is full */
+	SKB_DROP_REASON_FULL_RING,
+	/** @SKB_DROP_REASON_NOMEM: error due to OOM */
+	SKB_DROP_REASON_NOMEM,
+	/**
+	 * @SKB_DROP_REASON_HDR_TRUNC: failed to trunc/extract the header from
+	 * networking data, e.g., failed to pull the protocol header from
+	 * frags via pskb_may_pull()
+	 */
+	SKB_DROP_REASON_HDR_TRUNC,
+	/**
+	 * @SKB_DROP_REASON_TAP_FILTER: dropped by (ebpf) filter directly attached
+	 * to tun/tap, e.g., via TUNSETFILTEREBPF
+	 */
+	SKB_DROP_REASON_TAP_FILTER,
+	/**
+	 * @SKB_DROP_REASON_TAP_TXFILTER: dropped by tx filter implemented at
+	 * tun/tap, e.g., check_filter()
+	 */
+	SKB_DROP_REASON_TAP_TXFILTER,
+	/** @SKB_DROP_REASON_ICMP_CSUM: ICMP checksum error */
+	SKB_DROP_REASON_ICMP_CSUM,
+	/**
+	 * @SKB_DROP_REASON_INVALID_PROTO: the packet doesn't follow RFC 2211,
+	 * such as a broadcasts ICMP_TIMESTAMP
+	 */
+	SKB_DROP_REASON_INVALID_PROTO,
+	/**
+	 * @SKB_DROP_REASON_IP_INADDRERRORS: host unreachable, corresponding to
+	 * IPSTATS_MIB_INADDRERRORS
+	 */
+	SKB_DROP_REASON_IP_INADDRERRORS,
+	/**
+	 * @SKB_DROP_REASON_IP_INNOROUTES: network unreachable, corresponding to
+	 * IPSTATS_MIB_INADDRERRORS
+	 */
+	SKB_DROP_REASON_IP_INNOROUTES,
+	/**
+	 * @SKB_DROP_REASON_PKT_TOO_BIG: packet size is too big (maybe exceed the
+	 * MTU)
+	 */
+	SKB_DROP_REASON_PKT_TOO_BIG,
+	/** @SKB_DROP_REASON_DUP_FRAG: duplicate fragment */
+	SKB_DROP_REASON_DUP_FRAG,
+	/** @SKB_DROP_REASON_FRAG_REASM_TIMEOUT: fragment reassembly timeout */
+	SKB_DROP_REASON_FRAG_REASM_TIMEOUT,
+	/**
+	 * @SKB_DROP_REASON_FRAG_TOO_FAR: ipv4 fragment too far.
+	 * (/proc/sys/net/ipv4/ipfrag_max_dist)
+	 */
+	SKB_DROP_REASON_FRAG_TOO_FAR,
+	/**
+	 * @SKB_DROP_REASON_TCP_MINTTL: ipv4 ttl or ipv6 hoplimit below
+	 * the threshold (IP_MINTTL or IPV6_MINHOPCOUNT).
+	 */
+	SKB_DROP_REASON_TCP_MINTTL,
+	/** @SKB_DROP_REASON_IPV6_BAD_EXTHDR: Bad IPv6 extension header. */
+	SKB_DROP_REASON_IPV6_BAD_EXTHDR,
+	/** @SKB_DROP_REASON_IPV6_NDISC_FRAG: invalid frag (suppress_frag_ndisc). */
+	SKB_DROP_REASON_IPV6_NDISC_FRAG,
+	/** @SKB_DROP_REASON_IPV6_NDISC_HOP_LIMIT: invalid hop limit. */
+	SKB_DROP_REASON_IPV6_NDISC_HOP_LIMIT,
+	/** @SKB_DROP_REASON_IPV6_NDISC_BAD_CODE: invalid NDISC icmp6 code. */
+	SKB_DROP_REASON_IPV6_NDISC_BAD_CODE,
+	/** @SKB_DROP_REASON_IPV6_NDISC_BAD_OPTIONS: invalid NDISC options. */
+	SKB_DROP_REASON_IPV6_NDISC_BAD_OPTIONS,
+	/**
+	 * @SKB_DROP_REASON_IPV6_NDISC_NS_OTHERHOST: NEIGHBOUR SOLICITATION
+	 * for another host.
+	 */
+	SKB_DROP_REASON_IPV6_NDISC_NS_OTHERHOST,
+	/**
+	 * @SKB_DROP_REASON_MAX: the maximum of core drop reasons, which
+	 * shouldn't be used as a real 'reason' - only for tracing code gen
+	 */
+	SKB_DROP_REASON_MAX,
+
+	/**
+	 * @SKB_DROP_REASON_SUBSYS_MASK: subsystem mask in drop reasons,
+	 * see &enum skb_drop_reason_subsys
+	 */
+	SKB_DROP_REASON_SUBSYS_MASK = 0xffff0000,
+};
+
+#define SKB_DROP_REASON_SUBSYS_SHIFT	16
+
+#define SKB_DR_INIT(name, reason)				\
+	enum skb_drop_reason name = SKB_DROP_REASON_##reason
+#define SKB_DR(name)						\
+	SKB_DR_INIT(name, NOT_SPECIFIED)
+#define SKB_DR_SET(name, reason)				\
+	(name = SKB_DROP_REASON_##reason)
+#define SKB_DR_OR(name, reason)					\
+	do {							\
+		if (name == SKB_DROP_REASON_NOT_SPECIFIED ||	\
+		    name == SKB_NOT_DROPPED_YET)		\
+			SKB_DR_SET(name, reason);		\
+	} while (0)
+
+#endif

include/net/dropreason.h

···
 
 #ifndef _LINUX_DROPREASON_H
 #define _LINUX_DROPREASON_H
-
-#define DEFINE_DROP_REASON(FN, FNe)	\
-	FN(NOT_SPECIFIED)		\
-	FN(NO_SOCKET)			\
-	FN(PKT_TOO_SMALL)		\
-	FN(TCP_CSUM)			\
-	FN(SOCKET_FILTER)		\
-	FN(UDP_CSUM)			\
-	FN(NETFILTER_DROP)		\
-	FN(OTHERHOST)			\
-	FN(IP_CSUM)			\
-	FN(IP_INHDR)			\
-	FN(IP_RPFILTER)			\
-	FN(UNICAST_IN_L2_MULTICAST)	\
-	FN(XFRM_POLICY)			\
-	FN(IP_NOPROTO)			\
-	FN(SOCKET_RCVBUFF)		\
-	FN(PROTO_MEM)			\
-	FN(TCP_MD5NOTFOUND)		\
-	FN(TCP_MD5UNEXPECTED)		\
-	FN(TCP_MD5FAILURE)		\
-	FN(SOCKET_BACKLOG)		\
-	FN(TCP_FLAGS)			\
-	FN(TCP_ZEROWINDOW)		\
-	FN(TCP_OLD_DATA)		\
-	FN(TCP_OVERWINDOW)		\
-	FN(TCP_OFOMERGE)		\
-	FN(TCP_RFC7323_PAWS)		\
-	FN(TCP_INVALID_SEQUENCE)	\
-	FN(TCP_RESET)			\
-	FN(TCP_INVALID_SYN)		\
-	FN(TCP_CLOSE)			\
-	FN(TCP_FASTOPEN)		\
-	FN(TCP_OLD_ACK)			\
-	FN(TCP_TOO_OLD_ACK)		\
-	FN(TCP_ACK_UNSENT_DATA)		\
-	FN(TCP_OFO_QUEUE_PRUNE)		\
-	FN(TCP_OFO_DROP)		\
-	FN(IP_OUTNOROUTES)		\
-	FN(BPF_CGROUP_EGRESS)		\
-	FN(IPV6DISABLED)		\
-	FN(NEIGH_CREATEFAIL)		\
-	FN(NEIGH_FAILED)		\
-	FN(NEIGH_QUEUEFULL)		\
-	FN(NEIGH_DEAD)			\
-	FN(TC_EGRESS)			\
-	FN(QDISC_DROP)			\
-	FN(CPU_BACKLOG)			\
-	FN(XDP)				\
-	FN(TC_INGRESS)			\
-	FN(UNHANDLED_PROTO)		\
-	FN(SKB_CSUM)			\
-	FN(SKB_GSO_SEG)			\
-	FN(SKB_UCOPY_FAULT)		\
-	FN(DEV_HDR)			\
-	FN(DEV_READY)			\
-	FN(FULL_RING)			\
-	FN(NOMEM)			\
-	FN(HDR_TRUNC)			\
-	FN(TAP_FILTER)			\
-	FN(TAP_TXFILTER)		\
-	FN(ICMP_CSUM)			\
-	FN(INVALID_PROTO)		\
-	FN(IP_INADDRERRORS)		\
-	FN(IP_INNOROUTES)		\
-	FN(PKT_TOO_BIG)			\
-	FN(DUP_FRAG)			\
-	FN(FRAG_REASM_TIMEOUT)		\
-	FN(FRAG_TOO_FAR)		\
-	FN(TCP_MINTTL)			\
-	FN(IPV6_BAD_EXTHDR)		\
-	FN(IPV6_NDISC_FRAG)		\
-	FN(IPV6_NDISC_HOP_LIMIT)	\
-	FN(IPV6_NDISC_BAD_CODE)		\
-	FN(IPV6_NDISC_BAD_OPTIONS)	\
-	FN(IPV6_NDISC_NS_OTHERHOST)	\
-	FNe(MAX)
+#include <net/dropreason-core.h>
 
 /**
- * enum skb_drop_reason - the reasons of skb drops
- *
- * The reason of skb drop, which is used in kfree_skb_reason().
+ * enum skb_drop_reason_subsys - subsystem tag for (extended) drop reasons
  */
-enum skb_drop_reason {
+enum skb_drop_reason_subsys {
+	/** @SKB_DROP_REASON_SUBSYS_CORE: core drop reasons defined above */
+	SKB_DROP_REASON_SUBSYS_CORE,
+
 	/**
-	 * @SKB_NOT_DROPPED_YET: skb is not dropped yet (used for no-drop case)
+	 * @SKB_DROP_REASON_SUBSYS_MAC80211_UNUSABLE: mac80211 drop reasons
+	 * for unusable frames, see net/mac80211/drop.h
 	 */
-	SKB_NOT_DROPPED_YET = 0,
-	/** @SKB_CONSUMED: packet has been consumed */
-	SKB_CONSUMED,
-	/** @SKB_DROP_REASON_NOT_SPECIFIED: drop reason is not specified */
-	SKB_DROP_REASON_NOT_SPECIFIED,
-	/** @SKB_DROP_REASON_NO_SOCKET: socket not found */
-	SKB_DROP_REASON_NO_SOCKET,
-	/** @SKB_DROP_REASON_PKT_TOO_SMALL: packet size is too small */
-	SKB_DROP_REASON_PKT_TOO_SMALL,
-	/** @SKB_DROP_REASON_TCP_CSUM: TCP checksum error */
-	SKB_DROP_REASON_TCP_CSUM,
-	/** @SKB_DROP_REASON_SOCKET_FILTER: dropped by socket filter */
-	SKB_DROP_REASON_SOCKET_FILTER,
-	/** @SKB_DROP_REASON_UDP_CSUM: UDP checksum error */
-	SKB_DROP_REASON_UDP_CSUM,
-	/** @SKB_DROP_REASON_NETFILTER_DROP: dropped by netfilter */
-	SKB_DROP_REASON_NETFILTER_DROP,
+	SKB_DROP_REASON_SUBSYS_MAC80211_UNUSABLE,
+
 	/**
-	 * @SKB_DROP_REASON_OTHERHOST: packet don't belong to current host
-	 * (interface is in promisc mode)
+	 * @SKB_DROP_REASON_SUBSYS_MAC80211_MONITOR: mac80211 drop reasons
+	 * for frames still going to monitor, see net/mac80211/drop.h
 	 */
-	SKB_DROP_REASON_OTHERHOST,
-	/** @SKB_DROP_REASON_IP_CSUM: IP checksum error */
-	SKB_DROP_REASON_IP_CSUM,
-	/**
-	 * @SKB_DROP_REASON_IP_INHDR: there is something wrong with IP header (see
-	 * IPSTATS_MIB_INHDRERRORS)
-	 */
-	SKB_DROP_REASON_IP_INHDR,
-	/**
-	 * @SKB_DROP_REASON_IP_RPFILTER: IP rpfilter validate failed. see the
-	 * document for rp_filter in ip-sysctl.rst for more information
-	 */
-	SKB_DROP_REASON_IP_RPFILTER,
-	/**
-	 * @SKB_DROP_REASON_UNICAST_IN_L2_MULTICAST: destination address of L2 is
-	 * multicast, but L3 is unicast.
-	 */
-	SKB_DROP_REASON_UNICAST_IN_L2_MULTICAST,
-	/** @SKB_DROP_REASON_XFRM_POLICY: xfrm policy check failed */
-	SKB_DROP_REASON_XFRM_POLICY,
-	/** @SKB_DROP_REASON_IP_NOPROTO: no support for IP protocol */
-	SKB_DROP_REASON_IP_NOPROTO,
-	/** @SKB_DROP_REASON_SOCKET_RCVBUFF: socket receive buff is full */
-	SKB_DROP_REASON_SOCKET_RCVBUFF,
-	/**
-	 * @SKB_DROP_REASON_PROTO_MEM: proto memory limition, such as udp packet
-	 * drop out of udp_memory_allocated.
-	 */
-	SKB_DROP_REASON_PROTO_MEM,
-	/**
-	 * @SKB_DROP_REASON_TCP_MD5NOTFOUND: no MD5 hash and one expected,
-	 * corresponding to LINUX_MIB_TCPMD5NOTFOUND
-	 */
-	SKB_DROP_REASON_TCP_MD5NOTFOUND,
-	/**
-	 * @SKB_DROP_REASON_TCP_MD5UNEXPECTED: MD5 hash and we're not expecting
-	 * one, corresponding to LINUX_MIB_TCPMD5UNEXPECTED
-	 */
-	SKB_DROP_REASON_TCP_MD5UNEXPECTED,
-	/**
-	 * @SKB_DROP_REASON_TCP_MD5FAILURE: MD5 hash and its wrong, corresponding
-	 * to LINUX_MIB_TCPMD5FAILURE
-	 */
-	SKB_DROP_REASON_TCP_MD5FAILURE,
-	/**
-	 * @SKB_DROP_REASON_SOCKET_BACKLOG: failed to add skb to socket backlog (
-	 * see LINUX_MIB_TCPBACKLOGDROP)
-	 */
-	SKB_DROP_REASON_SOCKET_BACKLOG,
-	/** @SKB_DROP_REASON_TCP_FLAGS: TCP flags invalid */
-	SKB_DROP_REASON_TCP_FLAGS,
-	/**
-	 * @SKB_DROP_REASON_TCP_ZEROWINDOW: TCP receive window size is zero,
-	 * see LINUX_MIB_TCPZEROWINDOWDROP
-	 */
-	SKB_DROP_REASON_TCP_ZEROWINDOW,
-	/**
-	 * @SKB_DROP_REASON_TCP_OLD_DATA: the TCP data reveived is already
-	 * received before (spurious retrans may happened), see
-	 * LINUX_MIB_DELAYEDACKLOST
-	 */
-	SKB_DROP_REASON_TCP_OLD_DATA,
-	/**
-	 * @SKB_DROP_REASON_TCP_OVERWINDOW: the TCP data is out of window,
-	 * the seq of the first byte exceed the right edges of receive
-	 * window
-	 */
-	SKB_DROP_REASON_TCP_OVERWINDOW,
-	/**
-	 * @SKB_DROP_REASON_TCP_OFOMERGE: the data of skb is already in the ofo
-	 * queue, corresponding to LINUX_MIB_TCPOFOMERGE
-	 */
-	SKB_DROP_REASON_TCP_OFOMERGE,
-	/**
-	 * @SKB_DROP_REASON_TCP_RFC7323_PAWS: PAWS check, corresponding to
-	 * LINUX_MIB_PAWSESTABREJECTED
-	 */
-	SKB_DROP_REASON_TCP_RFC7323_PAWS,
-	/** @SKB_DROP_REASON_TCP_INVALID_SEQUENCE: Not acceptable SEQ field */
-	SKB_DROP_REASON_TCP_INVALID_SEQUENCE,
-	/** @SKB_DROP_REASON_TCP_RESET: Invalid RST packet */
-	SKB_DROP_REASON_TCP_RESET,
-	/**
-	 * @SKB_DROP_REASON_TCP_INVALID_SYN: Incoming packet has unexpected
-	 * SYN flag
-	 */
-	SKB_DROP_REASON_TCP_INVALID_SYN,
-	/** @SKB_DROP_REASON_TCP_CLOSE: TCP socket in CLOSE state */
-	SKB_DROP_REASON_TCP_CLOSE,
-	/** @SKB_DROP_REASON_TCP_FASTOPEN: dropped by FASTOPEN request socket */
-	SKB_DROP_REASON_TCP_FASTOPEN,
-	/** @SKB_DROP_REASON_TCP_OLD_ACK: TCP ACK is old, but in window */
-	SKB_DROP_REASON_TCP_OLD_ACK,
-	/** @SKB_DROP_REASON_TCP_TOO_OLD_ACK: TCP ACK is too old */
-	SKB_DROP_REASON_TCP_TOO_OLD_ACK,
-	/**
-	 * @SKB_DROP_REASON_TCP_ACK_UNSENT_DATA: TCP ACK for data we haven't
-	 * sent yet
-	 */
-	SKB_DROP_REASON_TCP_ACK_UNSENT_DATA,
-	/** @SKB_DROP_REASON_TCP_OFO_QUEUE_PRUNE: pruned from TCP OFO queue */
-	SKB_DROP_REASON_TCP_OFO_QUEUE_PRUNE,
-	/** @SKB_DROP_REASON_TCP_OFO_DROP: data already in receive queue */
-	SKB_DROP_REASON_TCP_OFO_DROP,
-	/** @SKB_DROP_REASON_IP_OUTNOROUTES: route lookup failed */
-	SKB_DROP_REASON_IP_OUTNOROUTES,
-	/**
-	 * @SKB_DROP_REASON_BPF_CGROUP_EGRESS: dropped by BPF_PROG_TYPE_CGROUP_SKB
-	 * eBPF program
-	 */
-	SKB_DROP_REASON_BPF_CGROUP_EGRESS,
-	/** @SKB_DROP_REASON_IPV6DISABLED: IPv6 is disabled on the device */
-	SKB_DROP_REASON_IPV6DISABLED,
-	/** @SKB_DROP_REASON_NEIGH_CREATEFAIL: failed to create neigh entry */
-	SKB_DROP_REASON_NEIGH_CREATEFAIL,
-	/** @SKB_DROP_REASON_NEIGH_FAILED: neigh entry in failed state */
-	SKB_DROP_REASON_NEIGH_FAILED,
-	/** @SKB_DROP_REASON_NEIGH_QUEUEFULL: arp_queue for neigh entry is full */
-	SKB_DROP_REASON_NEIGH_QUEUEFULL,
-	/** @SKB_DROP_REASON_NEIGH_DEAD: neigh entry is dead */
-	SKB_DROP_REASON_NEIGH_DEAD,
-	/** @SKB_DROP_REASON_TC_EGRESS: dropped in TC egress HOOK */
-	SKB_DROP_REASON_TC_EGRESS,
-	/**
-	 * @SKB_DROP_REASON_QDISC_DROP: dropped by qdisc when packet outputting (
-	 * failed to enqueue to current qdisc)
-	 */
-	SKB_DROP_REASON_QDISC_DROP,
-	/**
-	 * @SKB_DROP_REASON_CPU_BACKLOG: failed to enqueue the skb to the per CPU
-	 * backlog queue. This can be caused by backlog queue full (see
-	 * netdev_max_backlog in net.rst) or RPS flow limit
-	 */
-	SKB_DROP_REASON_CPU_BACKLOG,
-	/** @SKB_DROP_REASON_XDP: dropped by XDP in input path */
-	SKB_DROP_REASON_XDP,
-	/** @SKB_DROP_REASON_TC_INGRESS: dropped in TC ingress HOOK */
-	SKB_DROP_REASON_TC_INGRESS,
-	/** @SKB_DROP_REASON_UNHANDLED_PROTO: protocol not implemented or not supported */
-	SKB_DROP_REASON_UNHANDLED_PROTO,
-	/** @SKB_DROP_REASON_SKB_CSUM: sk_buff checksum computation error */
-	SKB_DROP_REASON_SKB_CSUM,
-	/** @SKB_DROP_REASON_SKB_GSO_SEG: gso segmentation error */
-	SKB_DROP_REASON_SKB_GSO_SEG,
-	/**
-	 * @SKB_DROP_REASON_SKB_UCOPY_FAULT: failed to copy data from user space,
-	 * e.g., via zerocopy_sg_from_iter() or skb_orphan_frags_rx()
-	 */
-	SKB_DROP_REASON_SKB_UCOPY_FAULT,
-	/** @SKB_DROP_REASON_DEV_HDR: device driver specific header/metadata is invalid */
-	SKB_DROP_REASON_DEV_HDR,
-	/**
-	 * @SKB_DROP_REASON_DEV_READY: the device is not ready to xmit/recv due to
-	 * any of its data structure that is not up/ready/initialized,
-	 * e.g., the IFF_UP is not set, or driver specific tun->tfiles[txq]
-	 * is not initialized
-	 */
-	SKB_DROP_REASON_DEV_READY,
-	/** @SKB_DROP_REASON_FULL_RING: ring buffer is full */
-	SKB_DROP_REASON_FULL_RING,
-	/** @SKB_DROP_REASON_NOMEM: error due to OOM */
-	SKB_DROP_REASON_NOMEM,
-	/**
-	 * @SKB_DROP_REASON_HDR_TRUNC: failed to trunc/extract the header from
-	 * networking data, e.g., failed to pull the protocol header from
-	 * frags via pskb_may_pull()
-	 */
-	SKB_DROP_REASON_HDR_TRUNC,
-	/**
-	 * @SKB_DROP_REASON_TAP_FILTER: dropped by (ebpf) filter directly attached
-	 * to tun/tap, e.g., via TUNSETFILTEREBPF
-	 */
-	SKB_DROP_REASON_TAP_FILTER,
-	/**
-	 * @SKB_DROP_REASON_TAP_TXFILTER: dropped by tx filter implemented at
-	 * tun/tap, e.g., check_filter()
-	 */
-	SKB_DROP_REASON_TAP_TXFILTER,
-	/** @SKB_DROP_REASON_ICMP_CSUM: ICMP checksum error */
-	SKB_DROP_REASON_ICMP_CSUM,
-	/**
-	 * @SKB_DROP_REASON_INVALID_PROTO: the packet doesn't follow RFC 2211,
-	 * such as a broadcasts ICMP_TIMESTAMP
-	 */
-	SKB_DROP_REASON_INVALID_PROTO,
-	/**
-	 * @SKB_DROP_REASON_IP_INADDRERRORS: host unreachable, corresponding to
-	 * IPSTATS_MIB_INADDRERRORS
-	 */
-	SKB_DROP_REASON_IP_INADDRERRORS,
-	/**
-	 * @SKB_DROP_REASON_IP_INNOROUTES: network unreachable, corresponding to
-	 * IPSTATS_MIB_INADDRERRORS
-	 */
-	SKB_DROP_REASON_IP_INNOROUTES,
-	/**
-	 * @SKB_DROP_REASON_PKT_TOO_BIG: packet size is too big (maybe exceed the
-	 * MTU)
-	 */
-	SKB_DROP_REASON_PKT_TOO_BIG,
-	/** @SKB_DROP_REASON_DUP_FRAG: duplicate fragment */
-	SKB_DROP_REASON_DUP_FRAG,
-	/** @SKB_DROP_REASON_FRAG_REASM_TIMEOUT: fragment reassembly timeout */
-	SKB_DROP_REASON_FRAG_REASM_TIMEOUT,
-	/**
-	 * @SKB_DROP_REASON_FRAG_TOO_FAR: ipv4 fragment too far.
-	 * (/proc/sys/net/ipv4/ipfrag_max_dist)
-	 */
-	SKB_DROP_REASON_FRAG_TOO_FAR,
-	/**
-	 * @SKB_DROP_REASON_TCP_MINTTL: ipv4 ttl or ipv6 hoplimit below
-	 * the threshold (IP_MINTTL or IPV6_MINHOPCOUNT).
-	 */
-	SKB_DROP_REASON_TCP_MINTTL,
-	/** @SKB_DROP_REASON_IPV6_BAD_EXTHDR: Bad IPv6 extension header. */
-	SKB_DROP_REASON_IPV6_BAD_EXTHDR,
-	/** @SKB_DROP_REASON_IPV6_NDISC_FRAG: invalid frag (suppress_frag_ndisc). */
-	SKB_DROP_REASON_IPV6_NDISC_FRAG,
-	/** @SKB_DROP_REASON_IPV6_NDISC_HOP_LIMIT: invalid hop limit. */
-	SKB_DROP_REASON_IPV6_NDISC_HOP_LIMIT,
-	/** @SKB_DROP_REASON_IPV6_NDISC_BAD_CODE: invalid NDISC icmp6 code. */
-	SKB_DROP_REASON_IPV6_NDISC_BAD_CODE,
-	/** @SKB_DROP_REASON_IPV6_NDISC_BAD_OPTIONS: invalid NDISC options. */
-	SKB_DROP_REASON_IPV6_NDISC_BAD_OPTIONS,
-	/** @SKB_DROP_REASON_IPV6_NDISC_NS_OTHERHOST: NEIGHBOUR SOLICITATION
-	 * for another host.
-	 */
-	SKB_DROP_REASON_IPV6_NDISC_NS_OTHERHOST,
-	/**
-	 * @SKB_DROP_REASON_MAX: the maximum of drop reason, which shouldn't be
-	 * used as a real 'reason'
-	 */
-	SKB_DROP_REASON_MAX,
+	SKB_DROP_REASON_SUBSYS_MAC80211_MONITOR,
+
+	/** @SKB_DROP_REASON_SUBSYS_NUM: number of subsystems defined */
+	SKB_DROP_REASON_SUBSYS_NUM
 };
 
-#define SKB_DR_INIT(name, reason)				\
-	enum skb_drop_reason name = SKB_DROP_REASON_##reason
-#define SKB_DR(name)						\
-	SKB_DR_INIT(name, NOT_SPECIFIED)
-#define SKB_DR_SET(name, reason)				\
-	(name = SKB_DROP_REASON_##reason)
-#define SKB_DR_OR(name, reason)					\
-	do {							\
-		if (name == SKB_DROP_REASON_NOT_SPECIFIED ||	\
-		    name == SKB_NOT_DROPPED_YET)		\
-			SKB_DR_SET(name, reason);		\
-	} while (0)
+struct drop_reason_list {
+	const char * const *reasons;
+	size_t n_reasons;
+};
 
-extern const char * const drop_reasons[];
+/* Note: due to dynamic registrations, access must be under RCU */
+extern const struct drop_reason_list __rcu *
+drop_reasons_by_subsys[SKB_DROP_REASON_SUBSYS_NUM];
+
+void drop_reasons_register_subsys(enum skb_drop_reason_subsys subsys,
+				  const struct drop_reason_list *list);
+void drop_reasons_unregister_subsys(enum skb_drop_reason_subsys subsys);
 
 #endif

include/net/inet_frag.h

···
 #include <linux/in6.h>
 #include <linux/rbtree_types.h>
 #include <linux/refcount.h>
-#include <net/dropreason.h>
+#include <net/dropreason-core.h>
 
 /* Per netns frag queues directory */
 struct fqdir {

net/core/drop_monitor.c

···
 #include <linux/workqueue.h>
 #include <linux/netlink.h>
 #include <linux/net_dropmon.h>
+#include <linux/bitfield.h>
 #include <linux/percpu.h>
 #include <linux/timer.h>
 #include <linux/bitops.h>
···
 #include <net/genetlink.h>
 #include <net/netevent.h>
 #include <net/flow_offload.h>
+#include <net/dropreason.h>
 #include <net/devlink.h>
 
 #include <trace/events/skb.h>
···
 	if (!nskb)
 		return;
 
-	if (unlikely(reason >= SKB_DROP_REASON_MAX || reason <= 0))
-		reason = SKB_DROP_REASON_NOT_SPECIFIED;
 	cb = NET_DM_SKB_CB(nskb);
 	cb->reason = reason;
 	cb->pc = location;
···
 }
 
 #define NET_DM_MAX_SYMBOL_LEN 40
+#define NET_DM_MAX_REASON_LEN 50
 
-static size_t net_dm_packet_report_size(size_t payload_len,
-					enum skb_drop_reason reason)
+static size_t net_dm_packet_report_size(size_t payload_len)
 {
 	size_t size;
 
···
 	       /* NET_DM_ATTR_PROTO */
 	       nla_total_size(sizeof(u16)) +
 	       /* NET_DM_ATTR_REASON */
-	       nla_total_size(strlen(drop_reasons[reason]) + 1) +
+	       nla_total_size(NET_DM_MAX_REASON_LEN + 1) +
 	       /* NET_DM_ATTR_PAYLOAD */
 	       nla_total_size(payload_len);
 }
···
 				     size_t payload_len)
 {
 	struct net_dm_skb_cb *cb = NET_DM_SKB_CB(skb);
+	const struct drop_reason_list *list = NULL;
+	unsigned int subsys, subsys_reason;
 	char buf[NET_DM_MAX_SYMBOL_LEN];
 	struct nlattr *attr;
 	void *hdr;
···
 			      NET_DM_ATTR_PAD))
 		goto nla_put_failure;
 
+	rcu_read_lock();
+	subsys = u32_get_bits(cb->reason, SKB_DROP_REASON_SUBSYS_MASK);
+	if (subsys < SKB_DROP_REASON_SUBSYS_NUM)
+		list = rcu_dereference(drop_reasons_by_subsys[subsys]);
+	subsys_reason = cb->reason & ~SKB_DROP_REASON_SUBSYS_MASK;
+	if (!list ||
+	    subsys_reason >= list->n_reasons ||
+	    !list->reasons[subsys_reason] ||
+	    strlen(list->reasons[subsys_reason]) > NET_DM_MAX_REASON_LEN) {
+		list = rcu_dereference(drop_reasons_by_subsys[SKB_DROP_REASON_SUBSYS_CORE]);
+		subsys_reason = SKB_DROP_REASON_NOT_SPECIFIED;
+	}
 	if (nla_put_string(msg, NET_DM_ATTR_REASON,
-			   drop_reasons[cb->reason]))
+			   list->reasons[subsys_reason])) {
+		rcu_read_unlock();
 		goto nla_put_failure;
+	}
+	rcu_read_unlock();
 
 	snprintf(buf, sizeof(buf), "%pS", cb->pc);
 	if (nla_put_string(msg, NET_DM_ATTR_SYMBOL, buf))
···
 	if (net_dm_trunc_len)
 		payload_len = min_t(size_t, net_dm_trunc_len, payload_len);
 
-	msg = nlmsg_new(net_dm_packet_report_size(payload_len,
-						  NET_DM_SKB_CB(skb)->reason),
-			GFP_KERNEL);
+	msg = nlmsg_new(net_dm_packet_report_size(payload_len), GFP_KERNEL);
 	if (!msg)
 		goto out;
 

net/core/skbuff.c

···
 #include <linux/scatterlist.h>
 #include <linux/errqueue.h>
 #include <linux/prefetch.h>
+#include <linux/bitfield.h>
 #include <linux/if_vlan.h>
 #include <linux/mpls.h>
 #include <linux/kcov.h>
···
 #include <net/mptcp.h>
 #include <net/mctp.h>
 #include <net/page_pool.h>
+#include <net/dropreason.h>
 
 #include <linux/uaccess.h>
 #include <trace/events/skb.h>
···
 
 #undef FN
 #define FN(reason) [SKB_DROP_REASON_##reason] = #reason,
-const char * const drop_reasons[] = {
+static const char * const drop_reasons[] = {
 	[SKB_CONSUMED] = "CONSUMED",
 	DEFINE_DROP_REASON(FN, FN)
 };
-EXPORT_SYMBOL(drop_reasons);
+
+static const struct drop_reason_list drop_reasons_core = {
+	.reasons = drop_reasons,
+	.n_reasons = ARRAY_SIZE(drop_reasons),
+};
+
+const struct drop_reason_list __rcu *
+drop_reasons_by_subsys[SKB_DROP_REASON_SUBSYS_NUM] = {
+	[SKB_DROP_REASON_SUBSYS_CORE] = RCU_INITIALIZER(&drop_reasons_core),
+};
+EXPORT_SYMBOL(drop_reasons_by_subsys);
+
+/**
+ * drop_reasons_register_subsys - register another drop reason subsystem
+ * @subsys: the subsystem to register, must not be the core
+ * @list: the list of drop reasons within the subsystem, must point to
+ *	a statically initialized list
+ */
+void drop_reasons_register_subsys(enum skb_drop_reason_subsys subsys,
+				  const struct drop_reason_list *list)
+{
+	if (WARN(subsys <= SKB_DROP_REASON_SUBSYS_CORE ||
+		 subsys >= ARRAY_SIZE(drop_reasons_by_subsys),
+		 "invalid subsystem %d\n", subsys))
+		return;
+
+	/* must point to statically allocated memory, so INIT is OK */
+	RCU_INIT_POINTER(drop_reasons_by_subsys[subsys], list);
+}
+EXPORT_SYMBOL_GPL(drop_reasons_register_subsys);
+
+/**
+ * drop_reasons_unregister_subsys - unregister a drop reason subsystem
+ * @subsys: the subsystem to remove, must not be the core
+ *
+ * Note: This will synchronize_rcu() to ensure no users when it returns.
+ */
+void drop_reasons_unregister_subsys(enum skb_drop_reason_subsys subsys)
+{
+	if (WARN(subsys <= SKB_DROP_REASON_SUBSYS_CORE ||
+		 subsys >= ARRAY_SIZE(drop_reasons_by_subsys),
+		 "invalid subsystem %d\n", subsys))
+		return;
+
+	RCU_INIT_POINTER(drop_reasons_by_subsys[subsys], NULL);
+
+	synchronize_rcu();
+}
+EXPORT_SYMBOL_GPL(drop_reasons_unregister_subsys);
 
 /**
  *	skb_panic - private function for out-of-line support
···
 	if (unlikely(!skb_unref(skb)))
 		return false;
 
-	DEBUG_NET_WARN_ON_ONCE(reason <= 0 || reason >= SKB_DROP_REASON_MAX);
+	DEBUG_NET_WARN_ON_ONCE(reason == SKB_NOT_DROPPED_YET ||
+			       u32_get_bits(reason,
+					    SKB_DROP_REASON_SUBSYS_MASK) >=
+				SKB_DROP_REASON_SUBSYS_NUM);
 
 	if (reason == SKB_CONSUMED)
 		trace_consume_skb(skb, __builtin_return_address(0));

net/mac80211/drop.h

···
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * mac80211 drop reason list
+ *
+ * Copyright (C) 2023 Intel Corporation
+ */
+
+#ifndef MAC80211_DROP_H
+#define MAC80211_DROP_H
+#include <net/dropreason.h>
+
+typedef unsigned int __bitwise ieee80211_rx_result;
+
+#define MAC80211_DROP_REASONS_MONITOR(R)	\
+	R(RX_DROP_M_UNEXPECTED_4ADDR_FRAME)	\
+	R(RX_DROP_M_BAD_BCN_KEYIDX)		\
+	R(RX_DROP_M_BAD_MGMT_KEYIDX)		\
+/* this line for the trailing \ - add before this */
+
+#define MAC80211_DROP_REASONS_UNUSABLE(R)	\
+	R(RX_DROP_U_MIC_FAIL)			\
+	R(RX_DROP_U_REPLAY)			\
+	R(RX_DROP_U_BAD_MMIE)			\
+/* this line for the trailing \ - add before this */
+
+/* having two enums allows for checking ieee80211_rx_result use with sparse */
+enum ___mac80211_drop_reason {
+/* if we get to the end of handlers with RX_CONTINUE this will be the reason */
+	___RX_CONTINUE	= SKB_CONSUMED,
+
+/* this never gets used as an argument to kfree_skb_reason() */
+	___RX_QUEUED	= SKB_NOT_DROPPED_YET,
+
+#define ENUM(x) ___ ## x,
+	___RX_DROP_MONITOR = SKB_DROP_REASON_SUBSYS_MAC80211_MONITOR <<
+		SKB_DROP_REASON_SUBSYS_SHIFT,
+	MAC80211_DROP_REASONS_MONITOR(ENUM)
+
+	___RX_DROP_UNUSABLE = SKB_DROP_REASON_SUBSYS_MAC80211_UNUSABLE <<
+		SKB_DROP_REASON_SUBSYS_SHIFT,
+	MAC80211_DROP_REASONS_UNUSABLE(ENUM)
+#undef ENUM
+};
+
+enum mac80211_drop_reason {
+	RX_CONTINUE	 = (__force ieee80211_rx_result)___RX_CONTINUE,
+	RX_QUEUED	 = (__force ieee80211_rx_result)___RX_QUEUED,
+	RX_DROP_MONITOR	 = (__force ieee80211_rx_result)___RX_DROP_MONITOR,
+	RX_DROP_UNUSABLE = (__force ieee80211_rx_result)___RX_DROP_UNUSABLE,
+#define DEF(x) x = (__force ieee80211_rx_result)___ ## x,
+	MAC80211_DROP_REASONS_MONITOR(DEF)
+	MAC80211_DROP_REASONS_UNUSABLE(DEF)
+#undef DEF
+};
+
+#endif /* MAC80211_DROP_H */

net/mac80211/ieee80211_i.h

···
 #include "key.h"
 #include "sta_info.h"
 #include "debug.h"
+#include "drop.h"
 
 extern const struct cfg80211_ops mac80211_config_ops;
 
···
 
 	unsigned int flags;
 };
-
-
-typedef unsigned __bitwise ieee80211_rx_result;
-#define RX_CONTINUE		((__force ieee80211_rx_result) 0u)
-#define RX_DROP_UNUSABLE	((__force ieee80211_rx_result) 1u)
-#define RX_DROP_MONITOR		((__force ieee80211_rx_result) 2u)
-#define RX_QUEUED		((__force ieee80211_rx_result) 3u)
 
 /**
  * enum ieee80211_packet_rx_flags - packet RX flags

net/mac80211/main.c

···
 #include <linux/bitmap.h>
 #include <linux/inetdevice.h>
 #include <net/net_namespace.h>
+#include <net/dropreason.h>
 #include <net/cfg80211.h>
 #include <net/addrconf.h>
 
···
 }
 EXPORT_SYMBOL(ieee80211_free_hw);
 
+static const char * const drop_reasons_monitor[] = {
+#define V(x)	#x,
+	[0] = "RX_DROP_MONITOR",
+	MAC80211_DROP_REASONS_MONITOR(V)
+};
+
+static struct drop_reason_list drop_reason_list_monitor = {
+	.reasons = drop_reasons_monitor,
+	.n_reasons = ARRAY_SIZE(drop_reasons_monitor),
+};
+
+static const char * const drop_reasons_unusable[] = {
+	[0] = "RX_DROP_UNUSABLE",
+	MAC80211_DROP_REASONS_UNUSABLE(V)
+#undef V
+};
+
+static struct drop_reason_list drop_reason_list_unusable = {
+	.reasons = drop_reasons_unusable,
+	.n_reasons = ARRAY_SIZE(drop_reasons_unusable),
+};
+
 static int __init ieee80211_init(void)
 {
 	struct sk_buff *skb;
···
 	if (ret)
 		goto err_netdev;
 
+	drop_reasons_register_subsys(SKB_DROP_REASON_SUBSYS_MAC80211_MONITOR,
+				     &drop_reason_list_monitor);
+	drop_reasons_register_subsys(SKB_DROP_REASON_SUBSYS_MAC80211_UNUSABLE,
+				     &drop_reason_list_unusable);
+
 	return 0;
  err_netdev:
 	rc80211_minstrel_exit();
···
 	ieee80211s_stop();
 
 	ieee80211_iface_exit();
+
+	drop_reasons_unregister_subsys(SKB_DROP_REASON_SUBSYS_MAC80211_MONITOR);
+	drop_reasons_unregister_subsys(SKB_DROP_REASON_SUBSYS_MAC80211_UNUSABLE);
 
 	rcu_barrier();
 }

net/mac80211/rx.c

···
 				cfg80211_rx_unexpected_4addr_frame(
 					rx->sdata->dev, sta->sta.addr,
 					GFP_ATOMIC);
-			return RX_DROP_MONITOR;
+			return RX_DROP_M_UNEXPECTED_4ADDR_FRAME;
 		}
 		/*
 		 * Update counter and free packet here to avoid
···
 				cfg80211_rx_unprot_mlme_mgmt(rx->sdata->dev,
 							     skb->data,
 							     skb->len);
-			return RX_DROP_MONITOR; /* unexpected BIP keyidx */
+			return RX_DROP_M_BAD_BCN_KEYIDX;
 		}
 
 		rx->key = ieee80211_rx_get_bigtk(rx, mmie_keyidx);
···
 
 		if (mmie_keyidx < NUM_DEFAULT_KEYS ||
 		    mmie_keyidx >= NUM_DEFAULT_KEYS + NUM_DEFAULT_MGMT_KEYS)
-			return RX_DROP_MONITOR; /* unexpected BIP keyidx */
+			return RX_DROP_M_BAD_MGMT_KEYIDX; /* unexpected BIP keyidx */
 		if (rx->link_sta) {
 			if (ieee80211_is_group_privacy_action(skb) &&
 			    test_sta_flag(rx->sta, WLAN_STA_MFP))
···
 }
 
 static void ieee80211_rx_cooked_monitor(struct ieee80211_rx_data *rx,
-					struct ieee80211_rate *rate)
+					struct ieee80211_rate *rate,
+					ieee80211_rx_result reason)
 {
 	struct ieee80211_sub_if_data *sdata;
 	struct ieee80211_local *local = rx->local;
···
 	}
 
  out_free_skb:
-	dev_kfree_skb(skb);
+	kfree_skb_reason(skb, (__force u32)reason);
 }
 
 static void ieee80211_rx_handlers_result(struct ieee80211_rx_data *rx,
 					 ieee80211_rx_result res)
 {
-	switch (res) {
-	case RX_DROP_MONITOR:
-		I802_DEBUG_INC(rx->sdata->local->rx_handlers_drop);
-		if (rx->sta)
-			rx->link_sta->rx_stats.dropped++;
-		fallthrough;
-	case RX_CONTINUE: {
-		struct ieee80211_rate *rate = NULL;
-		struct ieee80211_supported_band *sband;
-		struct ieee80211_rx_status *status;
+	struct ieee80211_rx_status *status = IEEE80211_SKB_RXCB(rx->skb);
+	struct ieee80211_supported_band *sband;
+	struct ieee80211_rate *rate = NULL;
 
-		status = IEEE80211_SKB_RXCB((rx->skb));
-
-		sband = rx->local->hw.wiphy->bands[status->band];
-		if (status->encoding == RX_ENC_LEGACY)
-			rate = &sband->bitrates[status->rate_idx];
-
-		ieee80211_rx_cooked_monitor(rx, rate);
-		break;
-		}
-	case RX_DROP_UNUSABLE:
-		I802_DEBUG_INC(rx->sdata->local->rx_handlers_drop);
-		if (rx->sta)
-			rx->link_sta->rx_stats.dropped++;
-		dev_kfree_skb(rx->skb);
-		break;
-	case RX_QUEUED:
+	if (res == RX_QUEUED) {
 		I802_DEBUG_INC(rx->sdata->local->rx_handlers_queued);
-		break;
+		return;
 	}
+
+	if (res != RX_CONTINUE) {
+		I802_DEBUG_INC(rx->sdata->local->rx_handlers_drop);
+		if (rx->sta)
+			rx->link_sta->rx_stats.dropped++;
+	}
+
+	if (u32_get_bits((__force u32)res, SKB_DROP_REASON_SUBSYS_MASK) ==
+			SKB_DROP_REASON_SUBSYS_MAC80211_UNUSABLE) {
+		kfree_skb_reason(rx->skb, (__force u32)res);
+		return;
+	}
+
+	sband = rx->local->hw.wiphy->bands[status->band];
+	if (status->encoding == RX_ENC_LEGACY)
+		rate = &sband->bitrates[status->rate_idx];
+
+	ieee80211_rx_cooked_monitor(rx, rate, res);
 }
 
 static void ieee80211_rx_handlers(struct ieee80211_rx_data *rx,

net/mac80211/wpa.c

···
 		if (res < 0 ||
 		    (!res && !(status->flag & RX_FLAG_ALLOW_SAME_PN))) {
 			key->u.ccmp.replays++;
-			return RX_DROP_UNUSABLE;
+			return RX_DROP_U_REPLAY;
 		}
 
 		if (!(status->flag & RX_FLAG_DECRYPTED)) {
···
 				    skb->data + hdrlen + IEEE80211_CCMP_HDR_LEN,
 				    data_len,
 				    skb->data + skb->len - mic_len))
-				return RX_DROP_UNUSABLE;
+				return RX_DROP_U_MIC_FAIL;
 		}
 
 		memcpy(key->u.ccmp.rx_pn[queue], pn, IEEE80211_CCMP_PN_LEN);
···
 		if (res < 0 ||
 		    (!res && !(status->flag & RX_FLAG_ALLOW_SAME_PN))) {
 			key->u.gcmp.replays++;
-			return RX_DROP_UNUSABLE;
+			return RX_DROP_U_REPLAY;
 		}
 
 		if (!(status->flag & RX_FLAG_DECRYPTED)) {
···
 				    data_len,
 				    skb->data + skb->len -
 				    IEEE80211_GCMP_MIC_LEN))
-				return RX_DROP_UNUSABLE;
+				return RX_DROP_U_MIC_FAIL;
 		}
 
 		memcpy(key->u.gcmp.rx_pn[queue], pn, IEEE80211_GCMP_PN_LEN);
···
 		(skb->data + skb->len - sizeof(*mmie));
 	if (mmie->element_id != WLAN_EID_MMIE ||
 	    mmie->length != sizeof(*mmie) - 2)
-		return RX_DROP_UNUSABLE; /* Invalid MMIE */
+		return RX_DROP_U_BAD_MMIE; /* Invalid MMIE */
 
 	bip_ipn_swap(ipn, mmie->sequence_number);
 
 	if (memcmp(ipn, key->u.aes_cmac.rx_pn, 6) <= 0) {
 		key->u.aes_cmac.replays++;
-		return RX_DROP_UNUSABLE;
+		return RX_DROP_U_REPLAY;
 	}
 
 	if (!(status->flag & RX_FLAG_DECRYPTED)) {
···
 				   skb->data + 24, skb->len - 24, mic);
 		if (crypto_memneq(mic, mmie->mic, sizeof(mmie->mic))) {
 			key->u.aes_cmac.icverrors++;
-			return RX_DROP_UNUSABLE;
+			return RX_DROP_U_MIC_FAIL;
 		}
 	}
 
···
 
 	if (memcmp(ipn, key->u.aes_cmac.rx_pn, 6) <= 0) {
 		key->u.aes_cmac.replays++;
-		return RX_DROP_UNUSABLE;
+		return RX_DROP_U_REPLAY;
 	}
 
 	if (!(status->flag & RX_FLAG_DECRYPTED)) {
···
 				       skb->data + 24, skb->len - 24, mic);
 		if (crypto_memneq(mic, mmie->mic, sizeof(mmie->mic))) {
 			key->u.aes_cmac.icverrors++;
-			return RX_DROP_UNUSABLE;
+			return RX_DROP_U_MIC_FAIL;
 		}
 	}
 
···
 		(skb->data + skb->len - sizeof(*mmie));
 	if (mmie->element_id != WLAN_EID_MMIE ||
 	    mmie->length != sizeof(*mmie) - 2)
-		return RX_DROP_UNUSABLE; /* Invalid MMIE */
+		return RX_DROP_U_BAD_MMIE; /* Invalid MMIE */
 
 	bip_ipn_swap(ipn, mmie->sequence_number);
 
 	if (memcmp(ipn, key->u.aes_gmac.rx_pn, 6) <= 0) {
 		key->u.aes_gmac.replays++;
-		return RX_DROP_UNUSABLE;
+		return RX_DROP_U_REPLAY;
 	}
 
 	if (!(status->flag & RX_FLAG_DECRYPTED)) {
···
 		    crypto_memneq(mic, mmie->mic, sizeof(mmie->mic))) {
 			key->u.aes_gmac.icverrors++;
 			kfree(mic);
-			return RX_DROP_UNUSABLE;
+			return RX_DROP_U_MIC_FAIL;
 		}
 		kfree(mic);
 	}