[PATCH v2 net-next 0/7] net: make TCP preemptible

[PATCH v2 net-next 0/7] net: make TCP preemptible

[Eric Dumazet]

Most of TCP stack assumed it was running from BH handler.

This is great for most things, as TCP behavior is very sensitive
to scheduling artifacts.

However, the prequeue and backlog processing are problematic,
as they need to be flushed with BH being blocked.

To cope with modern needs, TCP sockets have big sk_rcvbuf values,
in the order of 16 MB, and soon 32 MB.
This means that backlog can hold thousands of packets, and things
like TCP coalescing or collapsing on this amount of packets can
lead to insane latency spikes, since BH are blocked for too long.

It is time to make UDP/TCP stacks preemptible.

Note that fast path still runs from BH handler.

v2: Added "tcp: make tcp_sendmsg() aware of socket backlog"
    to reduce latency problems of large sends.

v3: Fixed a typo in tcp_cdg.c

Eric Dumazet (7):
  tcp: do not assume TCP code is non preemptible
  tcp: do not block bh during prequeue processing
  dccp: do not assume DCCP code is non preemptible
  udp: prepare for non BH masking at backlog processing
  sctp: prepare for socket backlog behavior change
  net: do not block BH while processing socket backlog
  tcp: make tcp_sendmsg() aware of socket backlog

 include/net/sock.h       |  11 +++++
 net/core/sock.c          |  29 +++++------
 net/dccp/input.c         |   2 +-
 net/dccp/ipv4.c          |   4 +-
 net/dccp/ipv6.c          |   4 +-
 net/dccp/options.c       |   2 +-
 net/ipv4/tcp.c           |  14 +++---
 net/ipv4/tcp_cdg.c       |  20 ++++----
 net/ipv4/tcp_cubic.c     |  20 ++++----
 net/ipv4/tcp_fastopen.c  |  12 ++---
 net/ipv4/tcp_input.c     | 126 +++++++++++++++++++----------------------------
 net/ipv4/tcp_ipv4.c      |  14 ++++--
 net/ipv4/tcp_minisocks.c |   2 +-
 net/ipv4/tcp_output.c    |  11 ++---
 net/ipv4/tcp_recovery.c  |   4 +-
 net/ipv4/tcp_timer.c     |  10 ++--
 net/ipv4/udp.c           |   4 +-
 net/ipv6/tcp_ipv6.c      |  12 ++---
 net/ipv6/udp.c           |   4 +-
 net/sctp/inqueue.c       |   2 +
 20 files changed, 150 insertions(+), 157 deletions(-)

-- 
2.8.0.rc3.226.g39d4020

[PATCH v3 net-next 1/7] tcp: do not assume TCP code is non preemptible

[Eric Dumazet]

We want to to make TCP stack preemptible, as draining prequeue
and backlog queues can take lot of time.

Many SNMP updates were assuming that BH (and preemption) was disabled.

Need to convert some __NET_INC_STATS() calls to NET_INC_STATS()
and some __TCP_INC_STATS() to TCP_INC_STATS()

Before using this_cpu_ptr(net->ipv4.tcp_sk) in tcp_v4_send_reset()
and tcp_v4_send_ack(), we add an explicit preempt disabled section.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
---
 net/ipv4/tcp.c           |  2 +-
 net/ipv4/tcp_cdg.c       | 20 +++++-----
 net/ipv4/tcp_cubic.c     | 20 +++++-----
 net/ipv4/tcp_fastopen.c  | 12 +++---
 net/ipv4/tcp_input.c     | 96 ++++++++++++++++++++++++------------------------
 net/ipv4/tcp_ipv4.c      | 14 ++++---
 net/ipv4/tcp_minisocks.c |  2 +-
 net/ipv4/tcp_output.c    | 11 +++---
 net/ipv4/tcp_recovery.c  |  4 +-
 net/ipv4/tcp_timer.c     | 10 +++--
 net/ipv6/tcp_ipv6.c      | 12 +++---
 11 files changed, 104 insertions(+), 99 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index cb4d1cabb42c..b24c6ed4a04f 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3095,7 +3095,7 @@ void tcp_done(struct sock *sk)
 	struct request_sock *req = tcp_sk(sk)->fastopen_rsk;
 
 	if (sk->sk_state == TCP_SYN_SENT || sk->sk_state == TCP_SYN_RECV)
-		__TCP_INC_STATS(sock_net(sk), TCP_MIB_ATTEMPTFAILS);
+		TCP_INC_STATS(sock_net(sk), TCP_MIB_ATTEMPTFAILS);
 
 	tcp_set_state(sk, TCP_CLOSE);
 	tcp_clear_xmit_timers(sk);
diff --git a/net/ipv4/tcp_cdg.c b/net/ipv4/tcp_cdg.c
index 3c00208c37f4..ccce8a55f1e1 100644
--- a/net/ipv4/tcp_cdg.c
+++ b/net/ipv4/tcp_cdg.c
@@ -155,11 +155,11 @@ static void tcp_cdg_hystart_update(struct sock *sk)
 
 			ca->last_ack = now_us;
 			if (after(now_us, ca->round_start + base_owd)) {
-				__NET_INC_STATS(sock_net(sk),
-						LINUX_MIB_TCPHYSTARTTRAINDETECT);
-				__NET_ADD_STATS(sock_net(sk),
-						LINUX_MIB_TCPHYSTARTTRAINCWND,
-						tp->snd_cwnd);
+				NET_INC_STATS(sock_net(sk),
+					      LINUX_MIB_TCPHYSTARTTRAINDETECT);
+				NET_ADD_STATS(sock_net(sk),
+					      LINUX_MIB_TCPHYSTARTTRAINCWND,
+					      tp->snd_cwnd);
 				tp->snd_ssthresh = tp->snd_cwnd;
 				return;
 			}
@@ -174,11 +174,11 @@ static void tcp_cdg_hystart_update(struct sock *sk)
 					 125U);
 
 			if (ca->rtt.min > thresh) {
-				__NET_INC_STATS(sock_net(sk),
-						LINUX_MIB_TCPHYSTARTDELAYDETECT);
-				__NET_ADD_STATS(sock_net(sk),
-						LINUX_MIB_TCPHYSTARTDELAYCWND,
-						tp->snd_cwnd);
+				NET_INC_STATS(sock_net(sk),
+					      LINUX_MIB_TCPHYSTARTDELAYDETECT);
+				NET_ADD_STATS(sock_net(sk),
+					      LINUX_MIB_TCPHYSTARTDELAYCWND,
+					      tp->snd_cwnd);
 				tp->snd_ssthresh = tp->snd_cwnd;
 			}
 		}
diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c
index 59155af9de5d..0ce946e395e1 100644
--- a/net/ipv4/tcp_cubic.c
+++ b/net/ipv4/tcp_cubic.c
@@ -402,11 +402,11 @@ static void hystart_update(struct sock *sk, u32 delay)
 			ca->last_ack = now;
 			if ((s32)(now - ca->round_start) > ca->delay_min >> 4) {
 				ca->found |= HYSTART_ACK_TRAIN;
-				__NET_INC_STATS(sock_net(sk),
-						LINUX_MIB_TCPHYSTARTTRAINDETECT);
-				__NET_ADD_STATS(sock_net(sk),
-						LINUX_MIB_TCPHYSTARTTRAINCWND,
-						tp->snd_cwnd);
+				NET_INC_STATS(sock_net(sk),
+					      LINUX_MIB_TCPHYSTARTTRAINDETECT);
+				NET_ADD_STATS(sock_net(sk),
+					      LINUX_MIB_TCPHYSTARTTRAINCWND,
+					      tp->snd_cwnd);
 				tp->snd_ssthresh = tp->snd_cwnd;
 			}
 		}
@@ -423,11 +423,11 @@ static void hystart_update(struct sock *sk, u32 delay)
 			if (ca->curr_rtt > ca->delay_min +
 			    HYSTART_DELAY_THRESH(ca->delay_min >> 3)) {
 				ca->found |= HYSTART_DELAY;
-				__NET_INC_STATS(sock_net(sk),
-						LINUX_MIB_TCPHYSTARTDELAYDETECT);
-				__NET_ADD_STATS(sock_net(sk),
-						LINUX_MIB_TCPHYSTARTDELAYCWND,
-						tp->snd_cwnd);
+				NET_INC_STATS(sock_net(sk),
+					      LINUX_MIB_TCPHYSTARTDELAYDETECT);
+				NET_ADD_STATS(sock_net(sk),
+					      LINUX_MIB_TCPHYSTARTDELAYCWND,
+					      tp->snd_cwnd);
 				tp->snd_ssthresh = tp->snd_cwnd;
 			}
 		}
diff --git a/net/ipv4/tcp_fastopen.c b/net/ipv4/tcp_fastopen.c
index a1498d507e42..54d9f9b0120f 100644
--- a/net/ipv4/tcp_fastopen.c
+++ b/net/ipv4/tcp_fastopen.c
@@ -255,9 +255,9 @@ static bool tcp_fastopen_queue_check(struct sock *sk)
 		spin_lock(&fastopenq->lock);
 		req1 = fastopenq->rskq_rst_head;
 		if (!req1 || time_after(req1->rsk_timer.expires, jiffies)) {
-			spin_unlock(&fastopenq->lock);
 			__NET_INC_STATS(sock_net(sk),
 					LINUX_MIB_TCPFASTOPENLISTENOVERFLOW);
+			spin_unlock(&fastopenq->lock);
 			return false;
 		}
 		fastopenq->rskq_rst_head = req1->dl_next;
@@ -282,7 +282,7 @@ struct sock *tcp_try_fastopen(struct sock *sk, struct sk_buff *skb,
 	struct sock *child;
 
 	if (foc->len == 0) /* Client requests a cookie */
-		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENCOOKIEREQD);
+		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENCOOKIEREQD);
 
 	if (!((sysctl_tcp_fastopen & TFO_SERVER_ENABLE) &&
 	      (syn_data || foc->len >= 0) &&
@@ -311,13 +311,13 @@ fastopen:
 		child = tcp_fastopen_create_child(sk, skb, dst, req);
 		if (child) {
 			foc->len = -1;
-			__NET_INC_STATS(sock_net(sk),
-					LINUX_MIB_TCPFASTOPENPASSIVE);
+			NET_INC_STATS(sock_net(sk),
+				      LINUX_MIB_TCPFASTOPENPASSIVE);
 			return child;
 		}
-		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENPASSIVEFAIL);
+		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENPASSIVEFAIL);
 	} else if (foc->len > 0) /* Client presents an invalid cookie */
-		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENPASSIVEFAIL);
+		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENPASSIVEFAIL);
 
 	valid_foc.exp = foc->exp;
 	*foc = valid_foc;
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 1fb19c91e091..ac85fb42a5a2 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -869,7 +869,7 @@ static void tcp_update_reordering(struct sock *sk, const int metric,
 		else
 			mib_idx = LINUX_MIB_TCPSACKREORDER;
 
-		__NET_INC_STATS(sock_net(sk), mib_idx);
+		NET_INC_STATS(sock_net(sk), mib_idx);
 #if FASTRETRANS_DEBUG > 1
 		pr_debug("Disorder%d %d %u f%u s%u rr%d\n",
 			 tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
@@ -1062,7 +1062,7 @@ static bool tcp_check_dsack(struct sock *sk, const struct sk_buff *ack_skb,
 	if (before(start_seq_0, TCP_SKB_CB(ack_skb)->ack_seq)) {
 		dup_sack = true;
 		tcp_dsack_seen(tp);
-		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKRECV);
+		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKRECV);
 	} else if (num_sacks > 1) {
 		u32 end_seq_1 = get_unaligned_be32(&sp[1].end_seq);
 		u32 start_seq_1 = get_unaligned_be32(&sp[1].start_seq);
@@ -1071,7 +1071,7 @@ static bool tcp_check_dsack(struct sock *sk, const struct sk_buff *ack_skb,
 		    !before(start_seq_0, start_seq_1)) {
 			dup_sack = true;
 			tcp_dsack_seen(tp);
-			__NET_INC_STATS(sock_net(sk),
+			NET_INC_STATS(sock_net(sk),
 					LINUX_MIB_TCPDSACKOFORECV);
 		}
 	}
@@ -1289,7 +1289,7 @@ static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *skb,
 
 	if (skb->len > 0) {
 		BUG_ON(!tcp_skb_pcount(skb));
-		__NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKSHIFTED);
+		NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKSHIFTED);
 		return false;
 	}
 
@@ -1314,7 +1314,7 @@ static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *skb,
 	tcp_unlink_write_queue(skb, sk);
 	sk_wmem_free_skb(sk, skb);
 
-	__NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKMERGED);
+	NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKMERGED);
 
 	return true;
 }
@@ -1473,7 +1473,7 @@ noop:
 	return skb;
 
 fallback:
-	__NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKSHIFTFALLBACK);
+	NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKSHIFTFALLBACK);
 	return NULL;
 }
 
@@ -1661,7 +1661,7 @@ tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb,
 				mib_idx = LINUX_MIB_TCPSACKDISCARD;
 			}
 
-			__NET_INC_STATS(sock_net(sk), mib_idx);
+			NET_INC_STATS(sock_net(sk), mib_idx);
 			if (i == 0)
 				first_sack_index = -1;
 			continue;
@@ -1913,7 +1913,7 @@ void tcp_enter_loss(struct sock *sk)
 	skb = tcp_write_queue_head(sk);
 	is_reneg = skb && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED);
 	if (is_reneg) {
-		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSACKRENEGING);
+		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSACKRENEGING);
 		tp->sacked_out = 0;
 		tp->fackets_out = 0;
 	}
@@ -2399,7 +2399,7 @@ static bool tcp_try_undo_recovery(struct sock *sk)
 		else
 			mib_idx = LINUX_MIB_TCPFULLUNDO;
 
-		__NET_INC_STATS(sock_net(sk), mib_idx);
+		NET_INC_STATS(sock_net(sk), mib_idx);
 	}
 	if (tp->snd_una == tp->high_seq && tcp_is_reno(tp)) {
 		/* Hold old state until something *above* high_seq
@@ -2421,7 +2421,7 @@ static bool tcp_try_undo_dsack(struct sock *sk)
 	if (tp->undo_marker && !tp->undo_retrans) {
 		DBGUNDO(sk, "D-SACK");
 		tcp_undo_cwnd_reduction(sk, false);
-		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKUNDO);
+		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKUNDO);
 		return true;
 	}
 	return false;
@@ -2436,9 +2436,9 @@ static bool tcp_try_undo_loss(struct sock *sk, bool frto_undo)
 		tcp_undo_cwnd_reduction(sk, true);
 
 		DBGUNDO(sk, "partial loss");
-		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPLOSSUNDO);
+		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPLOSSUNDO);
 		if (frto_undo)
-			__NET_INC_STATS(sock_net(sk),
+			NET_INC_STATS(sock_net(sk),
 					LINUX_MIB_TCPSPURIOUSRTOS);
 		inet_csk(sk)->icsk_retransmits = 0;
 		if (frto_undo || tcp_is_sack(tp))
@@ -2563,7 +2563,7 @@ static void tcp_mtup_probe_failed(struct sock *sk)
 
 	icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;
 	icsk->icsk_mtup.probe_size = 0;
-	__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMTUPFAIL);
+	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMTUPFAIL);
 }
 
 static void tcp_mtup_probe_success(struct sock *sk)
@@ -2583,7 +2583,7 @@ static void tcp_mtup_probe_success(struct sock *sk)
 	icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
 	icsk->icsk_mtup.probe_size = 0;
 	tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
-	__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMTUPSUCCESS);
+	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMTUPSUCCESS);
 }
 
 /* Do a simple retransmit without using the backoff mechanisms in
@@ -2647,7 +2647,7 @@ static void tcp_enter_recovery(struct sock *sk, bool ece_ack)
 	else
 		mib_idx = LINUX_MIB_TCPSACKRECOVERY;
 
-	__NET_INC_STATS(sock_net(sk), mib_idx);
+	NET_INC_STATS(sock_net(sk), mib_idx);
 
 	tp->prior_ssthresh = 0;
 	tcp_init_undo(tp);
@@ -2740,7 +2740,7 @@ static bool tcp_try_undo_partial(struct sock *sk, const int acked)
 
 		DBGUNDO(sk, "partial recovery");
 		tcp_undo_cwnd_reduction(sk, true);
-		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO);
+		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO);
 		tcp_try_keep_open(sk);
 		return true;
 	}
@@ -3434,7 +3434,7 @@ bool tcp_oow_rate_limited(struct net *net, const struct sk_buff *skb,
 		s32 elapsed = (s32)(tcp_time_stamp - *last_oow_ack_time);
 
 		if (0 <= elapsed && elapsed < sysctl_tcp_invalid_ratelimit) {
-			__NET_INC_STATS(net, mib_idx);
+			NET_INC_STATS(net, mib_idx);
 			return true;	/* rate-limited: don't send yet! */
 		}
 	}
@@ -3467,7 +3467,7 @@ static void tcp_send_challenge_ack(struct sock *sk, const struct sk_buff *skb)
 		challenge_count = 0;
 	}
 	if (++challenge_count <= sysctl_tcp_challenge_ack_limit) {
-		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPCHALLENGEACK);
+		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPCHALLENGEACK);
 		tcp_send_ack(sk);
 	}
 }
@@ -3516,7 +3516,7 @@ static void tcp_process_tlp_ack(struct sock *sk, u32 ack, int flag)
 		tcp_set_ca_state(sk, TCP_CA_CWR);
 		tcp_end_cwnd_reduction(sk);
 		tcp_try_keep_open(sk);
-		__NET_INC_STATS(sock_net(sk),
+		NET_INC_STATS(sock_net(sk),
 				LINUX_MIB_TCPLOSSPROBERECOVERY);
 	} else if (!(flag & (FLAG_SND_UNA_ADVANCED |
 			     FLAG_NOT_DUP | FLAG_DATA_SACKED))) {
@@ -3621,14 +3621,14 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
 
 		tcp_in_ack_event(sk, CA_ACK_WIN_UPDATE);
 
-		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPHPACKS);
+		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPHPACKS);
 	} else {
 		u32 ack_ev_flags = CA_ACK_SLOWPATH;
 
 		if (ack_seq != TCP_SKB_CB(skb)->end_seq)
 			flag |= FLAG_DATA;
 		else
-			__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPPUREACKS);
+			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPPUREACKS);
 
 		flag |= tcp_ack_update_window(sk, skb, ack, ack_seq);
 
@@ -4131,7 +4131,7 @@ static void tcp_dsack_set(struct sock *sk, u32 seq, u32 end_seq)
 		else
 			mib_idx = LINUX_MIB_TCPDSACKOFOSENT;
 
-		__NET_INC_STATS(sock_net(sk), mib_idx);
+		NET_INC_STATS(sock_net(sk), mib_idx);
 
 		tp->rx_opt.dsack = 1;
 		tp->duplicate_sack[0].start_seq = seq;
@@ -4155,7 +4155,7 @@ static void tcp_send_dupack(struct sock *sk, const struct sk_buff *skb)
 
 	if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
 	    before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
-		__NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
+		NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
 		tcp_enter_quickack_mode(sk);
 
 		if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
@@ -4305,7 +4305,7 @@ static bool tcp_try_coalesce(struct sock *sk,
 
 	atomic_add(delta, &sk->sk_rmem_alloc);
 	sk_mem_charge(sk, delta);
-	__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVCOALESCE);
+	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVCOALESCE);
 	TCP_SKB_CB(to)->end_seq = TCP_SKB_CB(from)->end_seq;
 	TCP_SKB_CB(to)->ack_seq = TCP_SKB_CB(from)->ack_seq;
 	TCP_SKB_CB(to)->tcp_flags |= TCP_SKB_CB(from)->tcp_flags;
@@ -4393,7 +4393,7 @@ static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb)
 	tcp_ecn_check_ce(tp, skb);
 
 	if (unlikely(tcp_try_rmem_schedule(sk, skb, skb->truesize))) {
-		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFODROP);
+		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFODROP);
 		tcp_drop(sk, skb);
 		return;
 	}
@@ -4402,7 +4402,7 @@ static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb)
 	tp->pred_flags = 0;
 	inet_csk_schedule_ack(sk);
 
-	__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFOQUEUE);
+	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFOQUEUE);
 	SOCK_DEBUG(sk, "out of order segment: rcv_next %X seq %X - %X\n",
 		   tp->rcv_nxt, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
 
@@ -4457,7 +4457,7 @@ static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb)
 	if (skb1 && before(seq, TCP_SKB_CB(skb1)->end_seq)) {
 		if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
 			/* All the bits are present. Drop. */
-			__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFOMERGE);
+			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFOMERGE);
 			tcp_drop(sk, skb);
 			skb = NULL;
 			tcp_dsack_set(sk, seq, end_seq);
@@ -4496,7 +4496,7 @@ static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb)
 		__skb_unlink(skb1, &tp->out_of_order_queue);
 		tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
 				 TCP_SKB_CB(skb1)->end_seq);
-		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFOMERGE);
+		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFOMERGE);
 		tcp_drop(sk, skb1);
 	}
 
@@ -4661,7 +4661,7 @@ queue_and_out:
 
 	if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
 		/* A retransmit, 2nd most common case.  Force an immediate ack. */
-		__NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
+		NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
 		tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
 
 out_of_window:
@@ -4707,7 +4707,7 @@ static struct sk_buff *tcp_collapse_one(struct sock *sk, struct sk_buff *skb,
 
 	__skb_unlink(skb, list);
 	__kfree_skb(skb);
-	__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVCOLLAPSED);
+	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVCOLLAPSED);
 
 	return next;
 }
@@ -4866,7 +4866,7 @@ static bool tcp_prune_ofo_queue(struct sock *sk)
 	bool res = false;
 
 	if (!skb_queue_empty(&tp->out_of_order_queue)) {
-		__NET_INC_STATS(sock_net(sk), LINUX_MIB_OFOPRUNED);
+		NET_INC_STATS(sock_net(sk), LINUX_MIB_OFOPRUNED);
 		__skb_queue_purge(&tp->out_of_order_queue);
 
 		/* Reset SACK state.  A conforming SACK implementation will
@@ -4895,7 +4895,7 @@ static int tcp_prune_queue(struct sock *sk)
 
 	SOCK_DEBUG(sk, "prune_queue: c=%x\n", tp->copied_seq);
 
-	__NET_INC_STATS(sock_net(sk), LINUX_MIB_PRUNECALLED);
+	NET_INC_STATS(sock_net(sk), LINUX_MIB_PRUNECALLED);
 
 	if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
 		tcp_clamp_window(sk);
@@ -4925,7 +4925,7 @@ static int tcp_prune_queue(struct sock *sk)
 	 * drop receive data on the floor.  It will get retransmitted
 	 * and hopefully then we'll have sufficient space.
 	 */
-	__NET_INC_STATS(sock_net(sk), LINUX_MIB_RCVPRUNED);
+	NET_INC_STATS(sock_net(sk), LINUX_MIB_RCVPRUNED);
 
 	/* Massive buffer overcommit. */
 	tp->pred_flags = 0;
@@ -5184,7 +5184,7 @@ static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
 	if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp &&
 	    tcp_paws_discard(sk, skb)) {
 		if (!th->rst) {
-			__NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
+			NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
 			if (!tcp_oow_rate_limited(sock_net(sk), skb,
 						  LINUX_MIB_TCPACKSKIPPEDPAWS,
 						  &tp->last_oow_ack_time))
@@ -5236,8 +5236,8 @@ static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
 	if (th->syn) {
 syn_challenge:
 		if (syn_inerr)
-			__TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
-		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNCHALLENGE);
+			TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
+		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNCHALLENGE);
 		tcp_send_challenge_ack(sk, skb);
 		goto discard;
 	}
@@ -5352,7 +5352,7 @@ void tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
 				tcp_data_snd_check(sk);
 				return;
 			} else { /* Header too small */
-				__TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
+				TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
 				goto discard;
 			}
 		} else {
@@ -5380,7 +5380,7 @@ void tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
 
 					__skb_pull(skb, tcp_header_len);
 					tcp_rcv_nxt_update(tp, TCP_SKB_CB(skb)->end_seq);
-					__NET_INC_STATS(sock_net(sk),
+					NET_INC_STATS(sock_net(sk),
 							LINUX_MIB_TCPHPHITSTOUSER);
 					eaten = 1;
 				}
@@ -5403,7 +5403,7 @@ void tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
 
 				tcp_rcv_rtt_measure_ts(sk, skb);
 
-				__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPHPHITS);
+				NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPHPHITS);
 
 				/* Bulk data transfer: receiver */
 				eaten = tcp_queue_rcv(sk, skb, tcp_header_len,
@@ -5460,8 +5460,8 @@ step5:
 	return;
 
 csum_error:
-	__TCP_INC_STATS(sock_net(sk), TCP_MIB_CSUMERRORS);
-	__TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
+	TCP_INC_STATS(sock_net(sk), TCP_MIB_CSUMERRORS);
+	TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
 
 discard:
 	tcp_drop(sk, skb);
@@ -5553,13 +5553,13 @@ static bool tcp_rcv_fastopen_synack(struct sock *sk, struct sk_buff *synack,
 				break;
 		}
 		tcp_rearm_rto(sk);
-		__NET_INC_STATS(sock_net(sk),
+		NET_INC_STATS(sock_net(sk),
 				LINUX_MIB_TCPFASTOPENACTIVEFAIL);
 		return true;
 	}
 	tp->syn_data_acked = tp->syn_data;
 	if (tp->syn_data_acked)
-		__NET_INC_STATS(sock_net(sk),
+		NET_INC_STATS(sock_net(sk),
 				LINUX_MIB_TCPFASTOPENACTIVE);
 
 	tcp_fastopen_add_skb(sk, synack);
@@ -5595,7 +5595,7 @@ static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
 		if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
 		    !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp,
 			     tcp_time_stamp)) {
-			__NET_INC_STATS(sock_net(sk),
+			NET_INC_STATS(sock_net(sk),
 					LINUX_MIB_PAWSACTIVEREJECTED);
 			goto reset_and_undo;
 		}
@@ -5965,7 +5965,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
 		    (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
 		     after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt))) {
 			tcp_done(sk);
-			__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
+			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
 			return 1;
 		}
 
@@ -6022,7 +6022,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
 		if (sk->sk_shutdown & RCV_SHUTDOWN) {
 			if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
 			    after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
-				__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
+				NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
 				tcp_reset(sk);
 				return 1;
 			}
@@ -6224,7 +6224,7 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
 	 * timeout.
 	 */
 	if (sk_acceptq_is_full(sk) && inet_csk_reqsk_queue_young(sk) > 1) {
-		__NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
+		NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
 		goto drop;
 	}
 
@@ -6271,7 +6271,7 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
 			if (dst && strict &&
 			    !tcp_peer_is_proven(req, dst, true,
 						tmp_opt.saw_tstamp)) {
-				__NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSPASSIVEREJECTED);
+				NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSPASSIVEREJECTED);
 				goto drop_and_release;
 			}
 		}
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 87b173b563b0..761bc492c5e3 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -692,6 +692,7 @@ static void tcp_v4_send_reset(const struct sock *sk, struct sk_buff *skb)
 		     offsetof(struct inet_timewait_sock, tw_bound_dev_if));
 
 	arg.tos = ip_hdr(skb)->tos;
+	preempt_disable();
 	ip_send_unicast_reply(*this_cpu_ptr(net->ipv4.tcp_sk),
 			      skb, &TCP_SKB_CB(skb)->header.h4.opt,
 			      ip_hdr(skb)->saddr, ip_hdr(skb)->daddr,
@@ -699,6 +700,7 @@ static void tcp_v4_send_reset(const struct sock *sk, struct sk_buff *skb)
 
 	__TCP_INC_STATS(net, TCP_MIB_OUTSEGS);
 	__TCP_INC_STATS(net, TCP_MIB_OUTRSTS);
+	preempt_enable();
 
 #ifdef CONFIG_TCP_MD5SIG
 out:
@@ -774,12 +776,14 @@ static void tcp_v4_send_ack(struct net *net,
 	if (oif)
 		arg.bound_dev_if = oif;
 	arg.tos = tos;
+	preempt_disable();
 	ip_send_unicast_reply(*this_cpu_ptr(net->ipv4.tcp_sk),
 			      skb, &TCP_SKB_CB(skb)->header.h4.opt,
 			      ip_hdr(skb)->saddr, ip_hdr(skb)->daddr,
 			      &arg, arg.iov[0].iov_len);
 
 	__TCP_INC_STATS(net, TCP_MIB_OUTSEGS);
+	preempt_enable();
 }
 
 static void tcp_v4_timewait_ack(struct sock *sk, struct sk_buff *skb)
@@ -1151,12 +1155,12 @@ static bool tcp_v4_inbound_md5_hash(const struct sock *sk,
 		return false;
 
 	if (hash_expected && !hash_location) {
-		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMD5NOTFOUND);
+		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMD5NOTFOUND);
 		return true;
 	}
 
 	if (!hash_expected && hash_location) {
-		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMD5UNEXPECTED);
+		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMD5UNEXPECTED);
 		return true;
 	}
 
@@ -1342,7 +1346,7 @@ struct sock *tcp_v4_syn_recv_sock(const struct sock *sk, struct sk_buff *skb,
 	return newsk;
 
 exit_overflow:
-	__NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
+	NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
 exit_nonewsk:
 	dst_release(dst);
 exit:
@@ -1432,8 +1436,8 @@ discard:
 	return 0;
 
 csum_err:
-	__TCP_INC_STATS(sock_net(sk), TCP_MIB_CSUMERRORS);
-	__TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
+	TCP_INC_STATS(sock_net(sk), TCP_MIB_CSUMERRORS);
+	TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
 	goto discard;
 }
 EXPORT_SYMBOL(tcp_v4_do_rcv);
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index ffbfecdae471..4b95ec4ed2c8 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -337,7 +337,7 @@ void tcp_time_wait(struct sock *sk, int state, int timeo)
 		 * socket up.  We've got bigger problems than
 		 * non-graceful socket closings.
 		 */
-		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPTIMEWAITOVERFLOW);
+		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPTIMEWAITOVERFLOW);
 	}
 
 	tcp_update_metrics(sk);
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 1a487ff95d4c..25d527922b18 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2221,14 +2221,13 @@ bool tcp_schedule_loss_probe(struct sock *sk)
 /* Thanks to skb fast clones, we can detect if a prior transmit of
  * a packet is still in a qdisc or driver queue.
  * In this case, there is very little point doing a retransmit !
- * Note: This is called from BH context only.
  */
 static bool skb_still_in_host_queue(const struct sock *sk,
 				    const struct sk_buff *skb)
 {
 	if (unlikely(skb_fclone_busy(sk, skb))) {
-		__NET_INC_STATS(sock_net(sk),
-				LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES);
+		NET_INC_STATS(sock_net(sk),
+			      LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES);
 		return true;
 	}
 	return false;
@@ -2290,7 +2289,7 @@ void tcp_send_loss_probe(struct sock *sk)
 	tp->tlp_high_seq = tp->snd_nxt;
 
 probe_sent:
-	__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPLOSSPROBES);
+	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPLOSSPROBES);
 	/* Reset s.t. tcp_rearm_rto will restart timer from now */
 	inet_csk(sk)->icsk_pending = 0;
 rearm_timer:
@@ -2699,7 +2698,7 @@ int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs)
 			tp->retrans_stamp = tcp_skb_timestamp(skb);
 
 	} else if (err != -EBUSY) {
-		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRETRANSFAIL);
+		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRETRANSFAIL);
 	}
 
 	if (tp->undo_retrans < 0)
@@ -2823,7 +2822,7 @@ begin_fwd:
 		if (tcp_retransmit_skb(sk, skb, segs))
 			return;
 
-		__NET_INC_STATS(sock_net(sk), mib_idx);
+		NET_INC_STATS(sock_net(sk), mib_idx);
 
 		if (tcp_in_cwnd_reduction(sk))
 			tp->prr_out += tcp_skb_pcount(skb);
diff --git a/net/ipv4/tcp_recovery.c b/net/ipv4/tcp_recovery.c
index e0d0afaf15be..e36df4fcfeba 100644
--- a/net/ipv4/tcp_recovery.c
+++ b/net/ipv4/tcp_recovery.c
@@ -65,8 +65,8 @@ int tcp_rack_mark_lost(struct sock *sk)
 			if (scb->sacked & TCPCB_SACKED_RETRANS) {
 				scb->sacked &= ~TCPCB_SACKED_RETRANS;
 				tp->retrans_out -= tcp_skb_pcount(skb);
-				__NET_INC_STATS(sock_net(sk),
-						LINUX_MIB_TCPLOSTRETRANSMIT);
+				NET_INC_STATS(sock_net(sk),
+					      LINUX_MIB_TCPLOSTRETRANSMIT);
 			}
 		} else if (!(scb->sacked & TCPCB_RETRANS)) {
 			/* Original data are sent sequentially so stop early
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index 35f643d8ffbb..debdd8b33e69 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -162,8 +162,8 @@ static int tcp_write_timeout(struct sock *sk)
 			if (tp->syn_fastopen || tp->syn_data)
 				tcp_fastopen_cache_set(sk, 0, NULL, true, 0);
 			if (tp->syn_data && icsk->icsk_retransmits == 1)
-				__NET_INC_STATS(sock_net(sk),
-						LINUX_MIB_TCPFASTOPENACTIVEFAIL);
+				NET_INC_STATS(sock_net(sk),
+					      LINUX_MIB_TCPFASTOPENACTIVEFAIL);
 		}
 		retry_until = icsk->icsk_syn_retries ? : net->ipv4.sysctl_tcp_syn_retries;
 		syn_set = true;
@@ -178,8 +178,8 @@ static int tcp_write_timeout(struct sock *sk)
 			    tp->bytes_acked <= tp->rx_opt.mss_clamp) {
 				tcp_fastopen_cache_set(sk, 0, NULL, true, 0);
 				if (icsk->icsk_retransmits == net->ipv4.sysctl_tcp_retries1)
-					__NET_INC_STATS(sock_net(sk),
-							LINUX_MIB_TCPFASTOPENACTIVEFAIL);
+					NET_INC_STATS(sock_net(sk),
+						      LINUX_MIB_TCPFASTOPENACTIVEFAIL);
 			}
 			/* Black hole detection */
 			tcp_mtu_probing(icsk, sk);
@@ -209,6 +209,7 @@ static int tcp_write_timeout(struct sock *sk)
 	return 0;
 }
 
+/* Called with BH disabled */
 void tcp_delack_timer_handler(struct sock *sk)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
@@ -493,6 +494,7 @@ out_reset_timer:
 out:;
 }
 
+/* Called with BH disabled */
 void tcp_write_timer_handler(struct sock *sk)
 {
 	struct inet_connection_sock *icsk = inet_csk(sk);
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 52914714b923..7bdc9c9c231b 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -649,12 +649,12 @@ static bool tcp_v6_inbound_md5_hash(const struct sock *sk,
 		return false;
 
 	if (hash_expected && !hash_location) {
-		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMD5NOTFOUND);
+		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMD5NOTFOUND);
 		return true;
 	}
 
 	if (!hash_expected && hash_location) {
-		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMD5UNEXPECTED);
+		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMD5UNEXPECTED);
 		return true;
 	}
 
@@ -825,9 +825,9 @@ static void tcp_v6_send_response(const struct sock *sk, struct sk_buff *skb, u32
 	if (!IS_ERR(dst)) {
 		skb_dst_set(buff, dst);
 		ip6_xmit(ctl_sk, buff, &fl6, NULL, tclass);
-		__TCP_INC_STATS(net, TCP_MIB_OUTSEGS);
+		TCP_INC_STATS(net, TCP_MIB_OUTSEGS);
 		if (rst)
-			__TCP_INC_STATS(net, TCP_MIB_OUTRSTS);
+			TCP_INC_STATS(net, TCP_MIB_OUTRSTS);
 		return;
 	}
 
@@ -1276,8 +1276,8 @@ discard:
 	kfree_skb(skb);
 	return 0;
 csum_err:
-	__TCP_INC_STATS(sock_net(sk), TCP_MIB_CSUMERRORS);
-	__TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
+	TCP_INC_STATS(sock_net(sk), TCP_MIB_CSUMERRORS);
+	TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
 	goto discard;
 
 
-- 
2.8.0.rc3.226.g39d4020

[PATCH v3 net-next 2/7] tcp: do not block bh during prequeue processing

[Eric Dumazet]

AFAIK, nothing in current TCP stack absolutely wants BH
being disabled once socket is owned by a thread running in
process context.

As mentioned in my prior patch ("tcp: give prequeue mode some care"),
processing a batch of packets might take time, better not block BH
at all.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
---
 net/ipv4/tcp.c       |  4 ----
 net/ipv4/tcp_input.c | 30 ++----------------------------
 2 files changed, 2 insertions(+), 32 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index b24c6ed4a04f..4787f86ae64c 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1449,12 +1449,8 @@ static void tcp_prequeue_process(struct sock *sk)
 
 	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPPREQUEUED);
 
-	/* RX process wants to run with disabled BHs, though it is not
-	 * necessary */
-	local_bh_disable();
 	while ((skb = __skb_dequeue(&tp->ucopy.prequeue)) != NULL)
 		sk_backlog_rcv(sk, skb);
-	local_bh_enable();
 
 	/* Clear memory counter. */
 	tp->ucopy.memory = 0;
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index ac85fb42a5a2..6171f92be090 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -4611,14 +4611,12 @@ static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
 
 			__set_current_state(TASK_RUNNING);
 
-			local_bh_enable();
 			if (!skb_copy_datagram_msg(skb, 0, tp->ucopy.msg, chunk)) {
 				tp->ucopy.len -= chunk;
 				tp->copied_seq += chunk;
 				eaten = (chunk == skb->len);
 				tcp_rcv_space_adjust(sk);
 			}
-			local_bh_disable();
 		}
 
 		if (eaten <= 0) {
@@ -5134,7 +5132,6 @@ static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen)
 	int chunk = skb->len - hlen;
 	int err;
 
-	local_bh_enable();
 	if (skb_csum_unnecessary(skb))
 		err = skb_copy_datagram_msg(skb, hlen, tp->ucopy.msg, chunk);
 	else
@@ -5146,32 +5143,9 @@ static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen)
 		tcp_rcv_space_adjust(sk);
 	}
 
-	local_bh_disable();
 	return err;
 }
 
-static __sum16 __tcp_checksum_complete_user(struct sock *sk,
-					    struct sk_buff *skb)
-{
-	__sum16 result;
-
-	if (sock_owned_by_user(sk)) {
-		local_bh_enable();
-		result = __tcp_checksum_complete(skb);
-		local_bh_disable();
-	} else {
-		result = __tcp_checksum_complete(skb);
-	}
-	return result;
-}
-
-static inline bool tcp_checksum_complete_user(struct sock *sk,
-					     struct sk_buff *skb)
-{
-	return !skb_csum_unnecessary(skb) &&
-	       __tcp_checksum_complete_user(sk, skb);
-}
-
 /* Does PAWS and seqno based validation of an incoming segment, flags will
  * play significant role here.
  */
@@ -5386,7 +5360,7 @@ void tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
 				}
 			}
 			if (!eaten) {
-				if (tcp_checksum_complete_user(sk, skb))
+				if (tcp_checksum_complete(skb))
 					goto csum_error;
 
 				if ((int)skb->truesize > sk->sk_forward_alloc)
@@ -5430,7 +5404,7 @@ no_ack:
 	}
 
 slow_path:
-	if (len < (th->doff << 2) || tcp_checksum_complete_user(sk, skb))
+	if (len < (th->doff << 2) || tcp_checksum_complete(skb))
 		goto csum_error;
 
 	if (!th->ack && !th->rst && !th->syn)
-- 
2.8.0.rc3.226.g39d4020

[PATCH v3 net-next 3/7] dccp: do not assume DCCP code is non preemptible

[Eric Dumazet]

DCCP uses the generic backlog code, and this will soon
be changed to not disable BH when protocol is called back.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
---
 net/dccp/input.c   | 2 +-
 net/dccp/ipv4.c    | 4 ++--
 net/dccp/ipv6.c    | 4 ++--
 net/dccp/options.c | 2 +-
 4 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/net/dccp/input.c b/net/dccp/input.c
index 2437ecc13b82..ba347184bda9 100644
--- a/net/dccp/input.c
+++ b/net/dccp/input.c
@@ -359,7 +359,7 @@ send_sync:
 		goto discard;
 	}
 
-	__DCCP_INC_STATS(DCCP_MIB_INERRS);
+	DCCP_INC_STATS(DCCP_MIB_INERRS);
 discard:
 	__kfree_skb(skb);
 	return 0;
diff --git a/net/dccp/ipv4.c b/net/dccp/ipv4.c
index a8164272e0f4..5c7e413a3ae4 100644
--- a/net/dccp/ipv4.c
+++ b/net/dccp/ipv4.c
@@ -533,8 +533,8 @@ static void dccp_v4_ctl_send_reset(const struct sock *sk, struct sk_buff *rxskb)
 	bh_unlock_sock(ctl_sk);
 
 	if (net_xmit_eval(err) == 0) {
-		__DCCP_INC_STATS(DCCP_MIB_OUTSEGS);
-		__DCCP_INC_STATS(DCCP_MIB_OUTRSTS);
+		DCCP_INC_STATS(DCCP_MIB_OUTSEGS);
+		DCCP_INC_STATS(DCCP_MIB_OUTRSTS);
 	}
 out:
 	 dst_release(dst);
diff --git a/net/dccp/ipv6.c b/net/dccp/ipv6.c
index 0f4eb4ea57a5..d176f4e66369 100644
--- a/net/dccp/ipv6.c
+++ b/net/dccp/ipv6.c
@@ -277,8 +277,8 @@ static void dccp_v6_ctl_send_reset(const struct sock *sk, struct sk_buff *rxskb)
 	if (!IS_ERR(dst)) {
 		skb_dst_set(skb, dst);
 		ip6_xmit(ctl_sk, skb, &fl6, NULL, 0);
-		__DCCP_INC_STATS(DCCP_MIB_OUTSEGS);
-		__DCCP_INC_STATS(DCCP_MIB_OUTRSTS);
+		DCCP_INC_STATS(DCCP_MIB_OUTSEGS);
+		DCCP_INC_STATS(DCCP_MIB_OUTRSTS);
 		return;
 	}
 
diff --git a/net/dccp/options.c b/net/dccp/options.c
index b82b7ee9a1d2..74d29c56c367 100644
--- a/net/dccp/options.c
+++ b/net/dccp/options.c
@@ -253,7 +253,7 @@ out_nonsensical_length:
 	return 0;
 
 out_invalid_option:
-	__DCCP_INC_STATS(DCCP_MIB_INVALIDOPT);
+	DCCP_INC_STATS(DCCP_MIB_INVALIDOPT);
 	rc = DCCP_RESET_CODE_OPTION_ERROR;
 out_featneg_failed:
 	DCCP_WARN("DCCP(%p): Option %d (len=%d) error=%u\n", sk, opt, len, rc);
-- 
2.8.0.rc3.226.g39d4020

[PATCH v3 net-next 4/7] udp: prepare for non BH masking at backlog processing

[Eric Dumazet]

UDP uses the generic socket backlog code, and this will soon
be changed to not disable BH when protocol is called back.

We need to use appropriate SNMP accessors.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
---
 net/ipv4/udp.c | 4 ++--
 net/ipv6/udp.c | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 093284c5c03b..f67f52ba4809 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1514,9 +1514,9 @@ static int __udp_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
 
 		/* Note that an ENOMEM error is charged twice */
 		if (rc == -ENOMEM)
-			__UDP_INC_STATS(sock_net(sk), UDP_MIB_RCVBUFERRORS,
+			UDP_INC_STATS(sock_net(sk), UDP_MIB_RCVBUFERRORS,
 					is_udplite);
-		__UDP_INC_STATS(sock_net(sk), UDP_MIB_INERRORS, is_udplite);
+		UDP_INC_STATS(sock_net(sk), UDP_MIB_INERRORS, is_udplite);
 		kfree_skb(skb);
 		trace_udp_fail_queue_rcv_skb(rc, sk);
 		return -1;
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index 1ba5a74ac18f..f911c63f79e6 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -570,9 +570,9 @@ static int __udpv6_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
 
 		/* Note that an ENOMEM error is charged twice */
 		if (rc == -ENOMEM)
-			__UDP6_INC_STATS(sock_net(sk),
+			UDP6_INC_STATS(sock_net(sk),
 					 UDP_MIB_RCVBUFERRORS, is_udplite);
-		__UDP6_INC_STATS(sock_net(sk), UDP_MIB_INERRORS, is_udplite);
+		UDP6_INC_STATS(sock_net(sk), UDP_MIB_INERRORS, is_udplite);
 		kfree_skb(skb);
 		return -1;
 	}
-- 
2.8.0.rc3.226.g39d4020

[PATCH v3 net-next 5/7] sctp: prepare for socket backlog behavior change

[Eric Dumazet]

sctp_inq_push() will soon be called without BH being blocked
when generic socket code flushes the socket backlog.

It is very possible SCTP can be converted to not rely on BH,
but this needs to be done by SCTP experts.

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 net/sctp/inqueue.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/sctp/inqueue.c b/net/sctp/inqueue.c
index b335ffcef0b9..9d87bba0ff1d 100644
--- a/net/sctp/inqueue.c
+++ b/net/sctp/inqueue.c
@@ -89,10 +89,12 @@ void sctp_inq_push(struct sctp_inq *q, struct sctp_chunk *chunk)
 	 * Eventually, we should clean up inqueue to not rely
 	 * on the BH related data structures.
 	 */
+	local_bh_disable();
 	list_add_tail(&chunk->list, &q->in_chunk_list);
 	if (chunk->asoc)
 		chunk->asoc->stats.ipackets++;
 	q->immediate.func(&q->immediate);
+	local_bh_enable();
 }
 
 /* Peek at the next chunk on the inqeue. */
-- 
2.8.0.rc3.226.g39d4020

[PATCH v3 net-next 6/7] net: do not block BH while processing socket backlog

[Eric Dumazet]

Socket backlog processing is a major latency source.

With current TCP socket sk_rcvbuf limits, I have sampled __release_sock()
holding cpu for more than 5 ms, and packets being dropped by the NIC
once ring buffer is filled.

All users are now ready to be called from process context,
we can unblock BH and let interrupts be serviced faster.

cond_resched_softirq() could be removed, as it has no more user.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
---
 net/core/sock.c | 22 ++++++++--------------
 1 file changed, 8 insertions(+), 14 deletions(-)

diff --git a/net/core/sock.c b/net/core/sock.c
index e16a5db853c6..70744dbb6c3f 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -2019,33 +2019,27 @@ static void __release_sock(struct sock *sk)
 	__releases(&sk->sk_lock.slock)
 	__acquires(&sk->sk_lock.slock)
 {
-	struct sk_buff *skb = sk->sk_backlog.head;
+	struct sk_buff *skb, *next;
 
-	do {
+	while ((skb = sk->sk_backlog.head) != NULL) {
 		sk->sk_backlog.head = sk->sk_backlog.tail = NULL;
-		bh_unlock_sock(sk);
 
-		do {
-			struct sk_buff *next = skb->next;
+		spin_unlock_bh(&sk->sk_lock.slock);
 
+		do {
+			next = skb->next;
 			prefetch(next);
 			WARN_ON_ONCE(skb_dst_is_noref(skb));
 			skb->next = NULL;
 			sk_backlog_rcv(sk, skb);
 
-			/*
-			 * We are in process context here with softirqs
-			 * disabled, use cond_resched_softirq() to preempt.
-			 * This is safe to do because we've taken the backlog
-			 * queue private:
-			 */
-			cond_resched_softirq();
+			cond_resched();
 
 			skb = next;
 		} while (skb != NULL);
 
-		bh_lock_sock(sk);
-	} while ((skb = sk->sk_backlog.head) != NULL);
+		spin_lock_bh(&sk->sk_lock.slock);
+	}
 
 	/*
 	 * Doing the zeroing here guarantee we can not loop forever
-- 
2.8.0.rc3.226.g39d4020

[PATCH v3 net-next 7/7] tcp: make tcp_sendmsg() aware of socket backlog

[Eric Dumazet]

Large sendmsg()/write() hold socket lock for the duration of the call,
unless sk->sk_sndbuf limit is hit. This is bad because incoming packets
are parked into socket backlog for a long time.
Critical decisions like fast retransmit might be delayed.
Receivers have to maintain a big out of order queue with additional cpu
overhead, and also possible stalls in TX once windows are full.

Bidirectional flows are particularly hurt since the backlog can become
quite big if the copy from user space triggers IO (page faults)

Some applications learnt to use sendmsg() (or sendmmsg()) with small
chunks to avoid this issue.

Kernel should know better, right ?

Add a generic sk_flush_backlog() helper and use it right
before a new skb is allocated. Typically we put 64KB of payload
per skb (unless MSG_EOR is requested) and checking socket backlog
every 64KB gives good results.

As a matter of fact, tests with TSO/GSO disabled give very nice
results, as we manage to keep a small write queue and smaller
perceived rtt.

Note that sk_flush_backlog() maintains socket ownership,
so is not equivalent to a {release_sock(sk); lock_sock(sk);},
to ensure implicit atomicity rules that sendmsg() was
giving to (possibly buggy) applications.

In this simple implementation, I chose to not call tcp_release_cb(),
but we might consider this later.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Alexei Starovoitov <ast@fb.com>
Cc: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
---
 include/net/sock.h | 11 +++++++++++
 net/core/sock.c    |  7 +++++++
 net/ipv4/tcp.c     |  8 ++++++--
 3 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/include/net/sock.h b/include/net/sock.h
index 3df778ccaa82..1dbb1f9f7c1b 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -926,6 +926,17 @@ void sk_stream_kill_queues(struct sock *sk);
 void sk_set_memalloc(struct sock *sk);
 void sk_clear_memalloc(struct sock *sk);
 
+void __sk_flush_backlog(struct sock *sk);
+
+static inline bool sk_flush_backlog(struct sock *sk)
+{
+	if (unlikely(READ_ONCE(sk->sk_backlog.tail))) {
+		__sk_flush_backlog(sk);
+		return true;
+	}
+	return false;
+}
+
 int sk_wait_data(struct sock *sk, long *timeo, const struct sk_buff *skb);
 
 struct request_sock_ops;
diff --git a/net/core/sock.c b/net/core/sock.c
index 70744dbb6c3f..f615e9391170 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -2048,6 +2048,13 @@ static void __release_sock(struct sock *sk)
 	sk->sk_backlog.len = 0;
 }
 
+void __sk_flush_backlog(struct sock *sk)
+{
+	spin_lock_bh(&sk->sk_lock.slock);
+	__release_sock(sk);
+	spin_unlock_bh(&sk->sk_lock.slock);
+}
+
 /**
  * sk_wait_data - wait for data to arrive at sk_receive_queue
  * @sk:    sock to wait on
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 4787f86ae64c..b945c2b046c5 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1136,11 +1136,12 @@ int tcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
 	/* This should be in poll */
 	sk_clear_bit(SOCKWQ_ASYNC_NOSPACE, sk);
 
-	mss_now = tcp_send_mss(sk, &size_goal, flags);
-
 	/* Ok commence sending. */
 	copied = 0;
 
+restart:
+	mss_now = tcp_send_mss(sk, &size_goal, flags);
+
 	err = -EPIPE;
 	if (sk->sk_err || (sk->sk_shutdown & SEND_SHUTDOWN))
 		goto out_err;
@@ -1166,6 +1167,9 @@ new_segment:
 			if (!sk_stream_memory_free(sk))
 				goto wait_for_sndbuf;
 
+			if (sk_flush_backlog(sk))
+				goto restart;
+
 			skb = sk_stream_alloc_skb(sk,
 						  select_size(sk, sg),
 						  sk->sk_allocation,
-- 
2.8.0.rc3.226.g39d4020

Re: [PATCH v3 net-next 6/7] net: do not block BH while processing socket backlog

[Alexei Starovoitov]

On 4/29/16 2:16 PM, Eric Dumazet wrote:
> Socket backlog processing is a major latency source.
>
> With current TCP socket sk_rcvbuf limits, I have sampled __release_sock()
> holding cpu for more than 5 ms, and packets being dropped by the NIC
> once ring buffer is filled.
>
> All users are now ready to be called from process context,
> we can unblock BH and let interrupts be serviced faster.
>
> cond_resched_softirq() could be removed, as it has no more user.
>
> Signed-off-by: Eric Dumazet<edumazet@google.com>
> Acked-by: Soheil Hassas Yeganeh<soheil@google.com>

Acked-by: Alexei Starovoitov <ast@kernel.org>

Re: [PATCH v3 net-next 2/7] tcp: do not block bh during prequeue processing

[Alexei Starovoitov]

On 4/29/16 2:16 PM, Eric Dumazet wrote:
> AFAIK, nothing in current TCP stack absolutely wants BH
> being disabled once socket is owned by a thread running in
> process context.
>
> As mentioned in my prior patch ("tcp: give prequeue mode some care"),
> processing a batch of packets might take time, better not block BH
> at all.
>
> Signed-off-by: Eric Dumazet<edumazet@google.com>
> Acked-by: Soheil Hassas Yeganeh<soheil@google.com>

Acked-by: Alexei Starovoitov <ast@kernel.org>

Re: [PATCH v3 net-next 5/7] sctp: prepare for socket backlog behavior change

[Marcelo Ricardo Leitner]

On Fri, Apr 29, 2016 at 02:16:51PM -0700, Eric Dumazet wrote:
> sctp_inq_push() will soon be called without BH being blocked
> when generic socket code flushes the socket backlog.
> 
> It is very possible SCTP can be converted to not rely on BH,
> but this needs to be done by SCTP experts.
> 
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Thanks

> ---
>  net/sctp/inqueue.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/net/sctp/inqueue.c b/net/sctp/inqueue.c
> index b335ffcef0b9..9d87bba0ff1d 100644
> --- a/net/sctp/inqueue.c
> +++ b/net/sctp/inqueue.c
> @@ -89,10 +89,12 @@ void sctp_inq_push(struct sctp_inq *q, struct sctp_chunk *chunk)
>  	 * Eventually, we should clean up inqueue to not rely
>  	 * on the BH related data structures.
>  	 */
> +	local_bh_disable();
>  	list_add_tail(&chunk->list, &q->in_chunk_list);
>  	if (chunk->asoc)
>  		chunk->asoc->stats.ipackets++;
>  	q->immediate.func(&q->immediate);
> +	local_bh_enable();
>  }
>  
>  /* Peek at the next chunk on the inqeue. */
> -- 
> 2.8.0.rc3.226.g39d4020
> 

[PATCH net-next] tcp: guarantee forward progress in tcp_sendmsg()

[Eric Dumazet]

From: Eric Dumazet <edumazet@google.com>

Under high rx pressure, it is possible tcp_sendmsg() never has a
chance to allocate an skb and loop forever as sk_flush_backlog()
would always return true.

Fix this by calling sk_flush_backlog() only if one skb had been
allocated and filled before last backlog check.

Fixes: d41a69f1d390 ("tcp: make tcp_sendmsg() aware of socket backlog")
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 net/ipv4/tcp.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index b945c2b046c5ead5503505f250c3c67761b284ae..5c7ed147449c1b7ba029b12e033ad779a631460a 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1084,6 +1084,7 @@ int tcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
 	struct sockcm_cookie sockc;
 	int flags, err, copied = 0;
 	int mss_now = 0, size_goal, copied_syn = 0;
+	bool process_backlog = false;
 	bool sg;
 	long timeo;
 
@@ -1167,9 +1168,10 @@ new_segment:
 			if (!sk_stream_memory_free(sk))
 				goto wait_for_sndbuf;
 
-			if (sk_flush_backlog(sk))
+			if (process_backlog && sk_flush_backlog(sk)) {
+				process_backlog = false;
 				goto restart;
-
+			}
 			skb = sk_stream_alloc_skb(sk,
 						  select_size(sk, sg),
 						  sk->sk_allocation,
@@ -1177,6 +1179,7 @@ new_segment:
 			if (!skb)
 				goto wait_for_memory;
 
+			process_backlog = true;
 			/*
 			 * Check whether we can use HW checksum.
 			 */

Re: [PATCH net-next] tcp: guarantee forward progress in tcp_sendmsg()

[Soheil Hassas Yeganeh]

On Tue, May 3, 2016 at 12:49 AM, Eric Dumazet <eric.dumazet@gmail.com> wrote:
> From: Eric Dumazet <edumazet@google.com>
>
> Under high rx pressure, it is possible tcp_sendmsg() never has a
> chance to allocate an skb and loop forever as sk_flush_backlog()
> would always return true.
>
> Fix this by calling sk_flush_backlog() only if one skb had been
> allocated and filled before last backlog check.
>
> Fixes: d41a69f1d390 ("tcp: make tcp_sendmsg() aware of socket backlog")
> Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
> ---
>  net/ipv4/tcp.c |    7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index b945c2b046c5ead5503505f250c3c67761b284ae..5c7ed147449c1b7ba029b12e033ad779a631460a 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -1084,6 +1084,7 @@ int tcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
>         struct sockcm_cookie sockc;
>         int flags, err, copied = 0;
>         int mss_now = 0, size_goal, copied_syn = 0;
> +       bool process_backlog = false;
>         bool sg;
>         long timeo;
>
> @@ -1167,9 +1168,10 @@ new_segment:
>                         if (!sk_stream_memory_free(sk))
>                                 goto wait_for_sndbuf;
>
> -                       if (sk_flush_backlog(sk))
> +                       if (process_backlog && sk_flush_backlog(sk)) {
> +                               process_backlog = false;
>                                 goto restart;
> -
> +                       }
>                         skb = sk_stream_alloc_skb(sk,
>                                                   select_size(sk, sg),
>                                                   sk->sk_allocation,
> @@ -1177,6 +1179,7 @@ new_segment:
>                         if (!skb)
>                                 goto wait_for_memory;
>
> +                       process_backlog = true;
>                         /*
>                          * Check whether we can use HW checksum.
>                          */
>
>

Nice catch! Thanks.

Re: [PATCH net-next] tcp: guarantee forward progress in tcp_sendmsg()

[David Miller]

From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Mon, 02 May 2016 21:49:25 -0700

> From: Eric Dumazet <edumazet@google.com>
> 
> Under high rx pressure, it is possible tcp_sendmsg() never has a
> chance to allocate an skb and loop forever as sk_flush_backlog()
> would always return true.
> 
> Fix this by calling sk_flush_backlog() only if one skb had been
> allocated and filled before last backlog check.
> 
> Fixes: d41a69f1d390 ("tcp: make tcp_sendmsg() aware of socket backlog")
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Applied.