[CRIU] [PATCH] tcp: fix retransmission in repair mode

[Andrey Vagin]

From: Andrey Vagin <avagin at parallels.com>

Currently if a socket has a few packet in a write queue,
a kernel bug may be triggered:

kernel BUG at net/ipv4/tcp_output.c:2330!
RIP: 0010:[<ffffffff8155784f>] tcp_retransmit_skb+0x5ff/0x610

According to the initial realization v3.4-rc2-963-gc0e88ff,
all skb-s should look like already posted. This patch fixes code
according with this sentence.

Here are three points, which were not done in the initial patch:
1. A tcp send head should not be changed
2. Initialize TSO state of a skb
3. Reset the retransmission time

Signed-off-by: Andrey Vagin <avagin at openvz.org>
---
 include/net/tcp.h     | 2 ++
 net/ipv4/tcp.c        | 6 ++++++
 net/ipv4/tcp_output.c | 3 ++-
 3 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 6feeccd..7582d4a 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -544,6 +544,8 @@ extern bool tcp_syn_flood_action(struct sock *sk,
 extern void tcp_push_one(struct sock *, unsigned int mss_now);
 extern void tcp_send_ack(struct sock *sk);
 extern void tcp_send_delayed_ack(struct sock *sk);
+extern int tcp_init_tso_segs(const struct sock *sk, struct sk_buff *skb,
+			     unsigned int mss_now);
 
 /* tcp_input.c */
 extern void tcp_cwnd_application_limited(struct sock *sk);
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index f32c02e..11d070e 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1196,6 +1196,12 @@ new_segment:
 			TCP_SKB_CB(skb)->end_seq += copy;
 			skb_shinfo(skb)->gso_segs = 0;
 
+			if (tp->repair) {
+				/* skb should look like already posted */
+				tcp_init_send_head(sk);
+				tcp_init_tso_segs(sk, skb, mss_now);
+				tp->packets_out += tcp_skb_pcount(skb);
+			}
 			from += copy;
 			copied += copy;
 			if ((seglen -= copy) == 0 && iovlen == 0)
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index cfe6ffe..3e95bc7 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1579,7 +1579,7 @@ static inline unsigned int tcp_cwnd_test(const struct tcp_sock *tp,
  * This must be invoked the first time we consider transmitting
  * SKB onto the wire.
  */
-static int tcp_init_tso_segs(const struct sock *sk, struct sk_buff *skb,
+int tcp_init_tso_segs(const struct sock *sk, struct sk_buff *skb,
 			     unsigned int mss_now)
 {
 	int tso_segs = tcp_skb_pcount(skb);
@@ -3140,6 +3140,7 @@ void tcp_send_window_probe(struct sock *sk)
 		tcp_sk(sk)->snd_wl1 = tcp_sk(sk)->rcv_nxt - 1;
 		tcp_sk(sk)->snd_nxt = tcp_sk(sk)->write_seq;
 		tcp_xmit_probe_skb(sk, 0);
+		tcp_rearm_rto(sk);
 	}
 }
 
-- 
1.7.11.7