tcp: fix tcp_xmit_retransmit_queue() after rbtree introduction

I tried to hard avoiding a call to rb_first() (via tcp_rtx_queue_head)
in tcp_xmit_retransmit_queue(). But this was probably too bold.

Quoting Yuchung :

We might miss re-arming the RTO if tp->retransmit_skb_hint is not NULL.
This can happen when RACK marks the first packet lost again and resets
tp->retransmit_skb_hint for example (tcp_rack_mark_skb_lost())

Fixes: 75c119afe14f ("tcp: implement rb-tree based retransmit queue")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 6 deletions

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 6c74f2a39778..53dc1267c85e 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2921,7 +2921,7 @@ int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs)
 void tcp_xmit_retransmit_queue(struct sock *sk)
 {
         const struct inet_connection_sock *icsk = inet_csk(sk);
-        struct sk_buff *skb, *rtx_head = NULL, *hole = NULL;
+        struct sk_buff *skb, *rtx_head, *hole = NULL;
         struct tcp_sock *tp = tcp_sk(sk);
         u32 max_segs;
         int mib_idx;
@@ -2929,11 +2929,8 @@ void tcp_xmit_retransmit_queue(struct sock *sk)
         if (!tp->packets_out)
                 return;
 
-        skb = tp->retransmit_skb_hint;
-        if (!skb) {
-                rtx_head = tcp_rtx_queue_head(sk);
-                skb = rtx_head;
-        }
+        rtx_head = tcp_rtx_queue_head(sk);
+        skb = tp->retransmit_skb_hint ?: rtx_head;
         max_segs = tcp_tso_segs(sk, tcp_current_mss(sk));
         skb_rbtree_walk_from(skb) {
                 __u8 sacked;