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

[Andrew Vagin]

On Tue, Nov 13, 2012 at 07:39:26PM +0400, Pavel Emelyanov wrote:
> 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_sendmsg
	sk_stream_alloc_skb
	skb_entail(sk, skb);
		tcp_add_write_queue_tail(sk, skb);
			sk->sk_send_head = skb;
> 
> > +				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.

Ok
> 
> >  	}
> >  }
> >  
> > 
> 
>