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

[Pavel Emelyanov]

On 11/13/2012 07:29 PM, Andrey Vagin wrote:
> 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);

When does new skb occur in the send_head?

> +				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);

This should be done in setsockopt after calling tcp_send_window_probe
since it has nothing to do with sending the probe.

>  	}
>  }
>  
>