net: Add and use skb_mark_not_on_list().

An SKB is not on a list if skb->next is NULL.

Codify this convention into a helper function and use it
where we are dequeueing an SKB and need to mark it as such.
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/skbuff.h

@@ -1339,6 +1339,11 @@ static inline void skb_zcopy_abort(struct sk_buff *skb)
 	}
 }
 
+static inline void skb_mark_not_on_list(struct sk_buff *skb)
+{
+	skb->next = NULL;
+}
+
 /**
  *	skb_queue_empty - check if a queue is empty
  *	@list: queue head

net/core/dev.c

@@ -3231,7 +3231,7 @@ struct sk_buff *dev_hard_start_xmit(struct sk_buff *first, struct net_device *de
 	while (skb) {
 		struct sk_buff *next = skb->next;
 
-		skb->next = NULL;
+		skb_mark_not_on_list(skb);
 		rc = xmit_one(skb, dev, txq, next != NULL);
 		if (unlikely(!dev_xmit_complete(rc))) {
 			skb->next = next;
@@ -3331,7 +3331,7 @@ struct sk_buff *validate_xmit_skb_list(struct sk_buff *skb, struct net_device *d
 
 	for (; skb != NULL; skb = next) {
 		next = skb->next;
-		skb->next = NULL;
+		skb_mark_not_on_list(skb);
 
 		/* in case skb wont be segmented, point to itself */
 		skb->prev = skb;
@@ -5296,7 +5296,7 @@ static void __napi_gro_flush_chain(struct napi_struct *napi, u32 index,
 		if (flush_old && NAPI_GRO_CB(skb)->age == jiffies)
 			return;
 		list_del(&skb->list);
-		skb->next = NULL;
+		skb_mark_not_on_list(skb);
 		napi_gro_complete(skb);
 		napi->gro_hash[index].count--;
 	}
@@ -5482,7 +5482,7 @@ static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff
 
 	if (pp) {
 		list_del(&pp->list);
-		pp->next = NULL;
+		skb_mark_not_on_list(pp);
 		napi_gro_complete(pp);
 		napi->gro_hash[hash].count--;
 	}

net/core/sock.c

@@ -2332,7 +2332,7 @@ static void __release_sock(struct sock *sk)
 			next = skb->next;
 			prefetch(next);
 			WARN_ON_ONCE(skb_dst_is_noref(skb));
-			skb->next = NULL;
+			skb_mark_not_on_list(skb);
 			sk_backlog_rcv(sk, skb);
 
 			cond_resched();

net/ieee802154/6lowpan/reassembly.c

@@ -260,7 +260,7 @@ static int lowpan_frag_reasm(struct lowpan_frag_queue *fq, struct sk_buff *prev,
 	}
 	sub_frag_mem_limit(fq->q.net, sum_truesize);
 
-	head->next = NULL;
+	skb_mark_not_on_list(head);
 	head->dev = ldev;
 	head->tstamp = fq->q.stamp;
 

net/ipv4/ip_fragment.c

@@ -623,7 +623,7 @@ static int ip_frag_reasm(struct ipq *qp, struct sk_buff *skb,
 	sub_frag_mem_limit(qp->q.net, head->truesize);
 
 	*nextp = NULL;
-	head->next = NULL;
+	skb_mark_not_on_list(head);
 	head->prev = NULL;
 	head->dev = dev;
 	head->tstamp = qp->q.stamp;

net/ipv4/ip_input.c

@@ -535,7 +535,7 @@ static void ip_sublist_rcv_finish(struct list_head *head)
 		/* Handle ip{6}_forward case, as sch_direct_xmit have
 		 * another kind of SKB-list usage (see validate_xmit_skb_list)
 		 */
-		skb->next = NULL;
+		skb_mark_not_on_list(skb);
 		dst_input(skb);
 	}
 }

net/ipv4/ip_output.c

@@ -278,7 +278,7 @@ static int ip_finish_output_gso(struct net *net, struct sock *sk,
 		struct sk_buff *nskb = segs->next;
 		int err;
 
-		segs->next = NULL;
+		skb_mark_not_on_list(segs);
 		err = ip_fragment(net, sk, segs, mtu, ip_finish_output2);
 
 		if (err && ret == 0)
@@ -684,7 +684,7 @@ int ip_do_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
 
 			skb = frag;
 			frag = skb->next;
-			skb->next = NULL;
+			skb_mark_not_on_list(skb);
 		}
 
 		if (err == 0) {

net/ipv6/ip6_output.c

@@ -727,7 +727,7 @@ int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
 
 			skb = frag;
 			frag = skb->next;
-			skb->next = NULL;
+			skb_mark_not_on_list(skb);
 		}
 
 		kfree(tmp_hdr);

net/ipv6/netfilter/nf_conntrack_reasm.c

@@ -449,7 +449,7 @@ nf_ct_frag6_reasm(struct frag_queue *fq, struct sk_buff *prev,  struct net_devic
 	sub_frag_mem_limit(fq->q.net, head->truesize);
 
 	head->ignore_df = 1;
-	head->next = NULL;
+	skb_mark_not_on_list(head);
 	head->dev = dev;
 	head->tstamp = fq->q.stamp;
 	ipv6_hdr(head)->payload_len = htons(payload_len);

net/ipv6/reassembly.c

@@ -388,7 +388,7 @@ static int ip6_frag_reasm(struct frag_queue *fq, struct sk_buff *prev,
 	}
 	sub_frag_mem_limit(fq->q.net, sum_truesize);
 
-	head->next = NULL;
+	skb_mark_not_on_list(head);
 	head->dev = dev;
 	head->tstamp = fq->q.stamp;
 	ipv6_hdr(head)->payload_len = htons(payload_len);

net/netfilter/nfnetlink_queue.c

@@ -764,7 +764,7 @@ __nfqnl_enqueue_packet_gso(struct net *net, struct nfqnl_instance *queue,
 		return ret;
 	}
 
-	skb->next = NULL;
+	skb_mark_not_on_list(skb);
 
 	entry_seg = nf_queue_entry_dup(entry);
 	if (entry_seg) {

net/rxrpc/input.c

@@ -259,7 +259,7 @@ static void rxrpc_rotate_tx_window(struct rxrpc_call *call, rxrpc_seq_t to,
 	while (list) {
 		skb = list;
 		list = skb->next;
-		skb->next = NULL;
+		skb_mark_not_on_list(skb);
 		rxrpc_free_skb(skb, rxrpc_skb_tx_freed);
 	}
 }

net/sched/sch_cake.c

@@ -812,7 +812,7 @@ static struct sk_buff *dequeue_head(struct cake_flow *flow)
 
 	if (skb) {
 		flow->head = skb->next;
-		skb->next = NULL;
+		skb_mark_not_on_list(skb);
 	}
 
 	return skb;
@@ -1252,7 +1252,7 @@ static struct sk_buff *cake_ack_filter(struct cake_sched_data *q,
 	else
 		flow->head = elig_ack->next;
 
-	elig_ack->next = NULL;
+	skb_mark_not_on_list(elig_ack);
 
 	return elig_ack;
 }
@@ -1675,7 +1675,7 @@ static s32 cake_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 
 		while (segs) {
 			nskb = segs->next;
-			segs->next = NULL;
+			skb_mark_not_on_list(segs);
 			qdisc_skb_cb(segs)->pkt_len = segs->len;
 			cobalt_set_enqueue_time(segs, now);
 			get_cobalt_cb(segs)->adjusted_len = cake_overhead(q,

net/sched/sch_fq.c

@@ -319,7 +319,7 @@ static struct sk_buff *fq_dequeue_head(struct Qdisc *sch, struct fq_flow *flow)
 
 	if (skb) {
 		flow->head = skb->next;
-		skb->next = NULL;
+		skb_mark_not_on_list(skb);
 		flow->qlen--;
 		qdisc_qstats_backlog_dec(sch, skb);
 		sch->q.qlen--;

net/sched/sch_fq_codel.c

@@ -124,7 +124,7 @@ static inline struct sk_buff *dequeue_head(struct fq_codel_flow *flow)
 	struct sk_buff *skb = flow->head;
 
 	flow->head = skb->next;
-	skb->next = NULL;
+	skb_mark_not_on_list(skb);
 	return skb;
 }
 

net/sched/sch_generic.c

@@ -184,7 +184,7 @@ static void try_bulk_dequeue_skb(struct Qdisc *q,
 		skb = nskb;
 		(*packets)++; /* GSO counts as one pkt */
 	}
-	skb->next = NULL;
+	skb_mark_not_on_list(skb);
 }
 
 /* This variant of try_bulk_dequeue_skb() makes sure
@@ -210,7 +210,7 @@ static void try_bulk_dequeue_skb_slow(struct Qdisc *q,
 		skb = nskb;
 	} while (++cnt < 8);
 	(*packets) += cnt;
-	skb->next = NULL;
+	skb_mark_not_on_list(skb);
 }
 
 /* Note that dequeue_skb can possibly return a SKB list (via skb->next).

net/sched/sch_hhf.c

@@ -330,7 +330,7 @@ static struct sk_buff *dequeue_head(struct wdrr_bucket *bucket)
 	struct sk_buff *skb = bucket->head;
 
 	bucket->head = skb->next;
-	skb->next = NULL;
+	skb_mark_not_on_list(skb);
 	return skb;
 }
 

net/sched/sch_netem.c

@@ -568,7 +568,7 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 	if (segs) {
 		while (segs) {
 			skb2 = segs->next;
-			segs->next = NULL;
+			skb_mark_not_on_list(segs);
 			qdisc_skb_cb(segs)->pkt_len = segs->len;
 			last_len = segs->len;
 			rc = qdisc_enqueue(segs, sch, to_free);

net/sched/sch_tbf.c

@@ -162,7 +162,7 @@ static int tbf_segment(struct sk_buff *skb, struct Qdisc *sch,
 	nb = 0;
 	while (segs) {
 		nskb = segs->next;
-		segs->next = NULL;
+		skb_mark_not_on_list(segs);
 		qdisc_skb_cb(segs)->pkt_len = segs->len;
 		len += segs->len;
 		ret = qdisc_enqueue(segs, q->qdisc, to_free);

net/tipc/bearer.c

@@ -577,7 +577,7 @@ static int tipc_l2_rcv_msg(struct sk_buff *skb, struct net_device *dev,
 		rcu_dereference_rtnl(orig_dev->tipc_ptr);
 	if (likely(b && test_bit(0, &b->up) &&
 		   (skb->pkt_type <= PACKET_MULTICAST))) {
-		skb->next = NULL;
+		skb_mark_not_on_list(skb);
 		tipc_rcv(dev_net(b->pt.dev), skb, b);
 		rcu_read_unlock();
 		return NET_RX_SUCCESS;

net/xfrm/xfrm_device.c

@@ -99,7 +99,7 @@ struct sk_buff *validate_xmit_xfrm(struct sk_buff *skb, netdev_features_t featur
 
 	do {
 		struct sk_buff *nskb = skb2->next;
-		skb2->next = NULL;
+		skb_mark_not_on_list(skb2);
 
 		xo = xfrm_offload(skb2);
 		xo->flags |= XFRM_DEV_RESUME;

net/xfrm/xfrm_output.c

@@ -189,7 +189,7 @@ static int xfrm_output_gso(struct net *net, struct sock *sk, struct sk_buff *skb
 		struct sk_buff *nskb = segs->next;
 		int err;
 
-		segs->next = NULL;
+		skb_mark_not_on_list(segs);
 		err = xfrm_output2(net, sk, segs);
 
 		if (unlikely(err)) {