diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 854ad65..a97ca8f 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -303,7 +303,11 @@ struct tcp_sock {
 
 /*
  *	Header prediction flags
- *	0x5?10 << 16 + snd_wnd in net byte order
+ *	S << 28 + TCP_FLAG_ACK + snd_wnd, in net byte order
+ *		(PSH flag is ignored)
+ *		S is 5 (no options), or 8 (timestamp aligned)
+ *	otherwise, 0 to turn it off -- for instance, when there are
+ *	holes in receive space.
  */
 	__be32	pred_flags;
 
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 56f0aec..ff2f1c3 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -315,13 +315,11 @@ extern int			tcp_ioctl(struct sock *sk,
 
 extern int			tcp_rcv_state_process(struct sock *sk, 
 						      struct sk_buff *skb,
-						      struct tcphdr *th,
-						      unsigned len);
+						      struct tcphdr *th);
 
 extern int			tcp_rcv_established(struct sock *sk, 
 						    struct sk_buff *skb,
-						    struct tcphdr *th, 
-						    unsigned len);
+						    struct tcphdr *th);
 
 extern void			tcp_rcv_space_adjust(struct sock *sk);
 
@@ -540,9 +538,19 @@ static inline u32 __tcp_set_rto(const struct tcp_sock *tp)
 	return (tp->srtt >> 3) + tp->rttvar;
 }
 
+static inline u8 __tcp_fast_path_header_length(const struct tcp_sock *tp)
+{
+	return tp->rx_opt.tstamp_ok
+		? sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED
+		: sizeof(struct tcphdr);
+}
+
 static inline void __tcp_fast_path_on(struct tcp_sock *tp, u32 snd_wnd)
 {
-	tp->pred_flags = htonl((tp->tcp_header_len << 26) |
+	/* See linux/tcp.h for pred_flags details.
+	 * 'S' (doff) is 32-bit words, convert from bytes: 26 = 28 - 2.
+	 */
+	tp->pred_flags = htonl((__tcp_fast_path_header_length(tp) << 26) |
 			       ntohl(TCP_FLAG_ACK) |
 			       snd_wnd);
 }
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 788851c..5541d08 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -154,7 +154,7 @@ static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb)
 			 * tcp header plus fixed timestamp option length.
 			 * Resulting "len" is MSS free of SACK jitter.
 			 */
-			len -= tcp_sk(sk)->tcp_header_len;
+			len -= __tcp_fast_path_header_length(tcp_sk(sk));
 			icsk->icsk_ack.last_seg_size = len;
 			if (len == lss) {
 				icsk->icsk_ack.rcv_mss = len;
@@ -5218,7 +5218,7 @@ discard:
  *	tcp_data_queue when everything is OK.
  */
 int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
-			struct tcphdr *th, unsigned len)
+			struct tcphdr *th)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 	int res;
@@ -5236,32 +5236,18 @@ int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
 	 *	Our current scheme is not silly either but we take the
 	 *	extra cost of the net_bh soft interrupt processing...
 	 *	We do checksum and copy also but from device to kernel.
+	 *
+	 *	See linux/tcp.h and net/tcp.h for pred_flags details.
 	 */
-
-	tp->rx_opt.saw_tstamp = 0;
-
-	/*	pred_flags is 0xS?10 << 16 + snd_wnd
-	 *	if header_prediction is to be made
-	 *	'S' will always be tp->tcp_header_len >> 2
-	 *	'?' will be 0 for the fast path, otherwise pred_flags is 0 to
-	 *  turn it off	(when there are holes in the receive
-	 *	 space for instance)
-	 *	PSH flag is ignored.
-	 */
-
 	if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags &&
 	    TCP_SKB_CB(skb)->seq == tp->rcv_nxt &&
 	    !after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) {
-		int tcp_header_len = tp->tcp_header_len;
-
-		/* Timestamp header prediction: tcp_header_len
-		 * is automatically equal to th->doff*4 due to pred_flags
-		 * match.
-		 */
+		int tcp_header_len = tcp_header_len_th(th);
 
-		/* Check timestamp */
-		if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) {
-			/* No? Slow path! */
+		/* Timestamp header prediction */
+		if (tcp_header_len != sizeof(*th) + TCPOLEN_TSTAMP_ALIGNED) {
+			tp->rx_opt.saw_tstamp = 0; /* false */
+		} else {
 			if (!tcp_parse_aligned_timestamp(tp, th))
 				goto slow_path;
 
@@ -5276,35 +5262,12 @@ int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
 			 */
 		}
 
-		if (len <= tcp_header_len) {
-			/* Bulk data transfer: sender */
-			if (len == tcp_header_len) {
-				/* Predicted packet is in window by definition.
-				 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
-				 * Hence, check seq<=rcv_wup reduces to:
-				 */
-				if (tcp_header_len ==
-				    (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
-				    tp->rcv_nxt == tp->rcv_wup)
-					tcp_store_ts_recent(tp);
-
-				/* We know that such packets are checksummed
-				 * on entry.
-				 */
-				tcp_ack(sk, skb, 0);
-				__kfree_skb(skb);
-				tcp_data_snd_check(sk);
-				return 0;
-			} else { /* Header too small */
-				TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
-				goto discard;
-			}
-		} else {
+		if (tcp_header_len < skb->len) {
 			int eaten = 0;
 			int copied_early = 0;
 
 			if (tp->copied_seq == tp->rcv_nxt &&
-			    len - tcp_header_len <= tp->ucopy.len) {
+			    skb->len - tcp_header_len <= tp->ucopy.len) {
 #ifdef CONFIG_NET_DMA
 				if (tcp_dma_try_early_copy(sk, skb, tcp_header_len)) {
 					copied_early = 1;
@@ -5323,9 +5286,7 @@ int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
 					 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
 					 * Hence, check seq<=rcv_wup reduces to:
 					 */
-					if (tcp_header_len ==
-					    (sizeof(struct tcphdr) +
-					     TCPOLEN_TSTAMP_ALIGNED) &&
+					if (tp->rx_opt.saw_tstamp &&
 					    tp->rcv_nxt == tp->rcv_wup)
 						tcp_store_ts_recent(tp);
 
@@ -5346,8 +5307,7 @@ int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
 				 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
 				 * Hence, check seq<=rcv_wup reduces to:
 				 */
-				if (tcp_header_len ==
-				    (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
+				if (tp->rx_opt.saw_tstamp &&
 				    tp->rcv_nxt == tp->rcv_wup)
 					tcp_store_ts_recent(tp);
 
@@ -5388,11 +5348,33 @@ no_ack:
 			else
 				sk->sk_data_ready(sk, 0);
 			return 0;
+		} else {
+			/* Bulk data transfer: sender
+			 *
+			 * tcp_header_len > skb->len never happens,
+			 * already checked by tcp_v[4,6]_rcv()
+			 *
+			 * Predicted packet is in window by definition.
+			 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
+			 * Hence, check seq<=rcv_wup reduces to:
+			 */
+			if (tp->rx_opt.saw_tstamp &&
+			    tp->rcv_nxt == tp->rcv_wup)
+				tcp_store_ts_recent(tp);
+
+			/* We know that such packets are checksummed
+			 * on entry.
+			 */
+			tcp_ack(sk, skb, 0);
+			__kfree_skb(skb);
+			tcp_data_snd_check(sk);
+			return 0;
 		}
 	}
 
 slow_path:
-	if (len < (th->doff << 2) || tcp_checksum_complete_user(sk, skb))
+	/* Assumes skb->len includes header and options */
+	if (tcp_checksum_complete_user(sk, skb))
 		goto csum_error;
 
 	/*
@@ -5428,7 +5410,7 @@ discard:
 }
 
 static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
-					 struct tcphdr *th, unsigned len)
+					 struct tcphdr *th)
 {
 	u8 *hash_location;
 	struct inet_connection_sock *icsk = inet_csk(sk);
@@ -5705,7 +5687,7 @@ reset_and_undo:
  */
 
 int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
-			  struct tcphdr *th, unsigned len)
+			  struct tcphdr *th)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct inet_connection_sock *icsk = inet_csk(sk);
@@ -5752,7 +5734,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
 		goto discard;
 
 	case TCP_SYN_SENT:
-		queued = tcp_rcv_synsent_state_process(sk, skb, th, len);
+		queued = tcp_rcv_synsent_state_process(sk, skb, th);
 		if (queued >= 0)
 			return queued;
 
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index c206024..1860590 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1553,7 +1553,7 @@ int tcp_v4_do_rcv(struct sock *sk, struct sk_buff *skb)
 
 	if (sk->sk_state == TCP_ESTABLISHED) { /* Fast path */
 		TCP_CHECK_TIMER(sk);
-		if (tcp_rcv_established(sk, skb, tcp_hdr(skb), skb->len)) {
+		if (tcp_rcv_established(sk, skb, tcp_hdr(skb))) {
 			rsk = sk;
 			goto reset;
 		}
@@ -1580,7 +1580,7 @@ int tcp_v4_do_rcv(struct sock *sk, struct sk_buff *skb)
 	}
 
 	TCP_CHECK_TIMER(sk);
-	if (tcp_rcv_state_process(sk, skb, tcp_hdr(skb), skb->len)) {
+	if (tcp_rcv_state_process(sk, skb, tcp_hdr(skb))) {
 		rsk = sk;
 		goto reset;
 	}
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index f206ee5..37b7536 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -718,8 +718,7 @@ int tcp_child_process(struct sock *parent, struct sock *child,
 	int state = child->sk_state;
 
 	if (!sock_owned_by_user(child)) {
-		ret = tcp_rcv_state_process(child, skb, tcp_hdr(skb),
-					    skb->len);
+		ret = tcp_rcv_state_process(child, skb, tcp_hdr(skb));
 		/* Wakeup parent, send SIGIO */
 		if (state == TCP_SYN_RECV && child->sk_state != state)
 			parent->sk_data_ready(parent, 0);
diff --git a/net/ipv4/tcp_probe.c b/net/ipv4/tcp_probe.c
index 9bc805d..de2a32e 100644
--- a/net/ipv4/tcp_probe.c
+++ b/net/ipv4/tcp_probe.c
@@ -88,7 +88,7 @@ static inline int tcp_probe_avail(void)
  * Note: arguments must match tcp_rcv_established()!
  */
 static int jtcp_rcv_established(struct sock *sk, struct sk_buff *skb,
-			       struct tcphdr *th, unsigned len)
+			       struct tcphdr *th)
 {
 	const struct tcp_sock *tp = tcp_sk(sk);
 	const struct inet_sock *inet = inet_sk(sk);
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 04814bf..39e0d89 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1594,7 +1594,7 @@ static int tcp_v6_do_rcv(struct sock *sk, struct sk_buff *skb)
 
 	if (sk->sk_state == TCP_ESTABLISHED) { /* Fast path */
 		TCP_CHECK_TIMER(sk);
-		if (tcp_rcv_established(sk, skb, tcp_hdr(skb), skb->len))
+		if (tcp_rcv_established(sk, skb, tcp_hdr(skb)))
 			goto reset;
 		TCP_CHECK_TIMER(sk);
 		if (opt_skb)
@@ -1626,7 +1626,7 @@ static int tcp_v6_do_rcv(struct sock *sk, struct sk_buff *skb)
 	}
 
 	TCP_CHECK_TIMER(sk);
-	if (tcp_rcv_state_process(sk, skb, tcp_hdr(skb), skb->len))
+	if (tcp_rcv_state_process(sk, skb, tcp_hdr(skb)))
 		goto reset;
 	TCP_CHECK_TIMER(sk);
 	if (opt_skb)
-- 
1.6.3.3