tcp: do not assume TCP code is non preemptible

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>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 6 deletions

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);