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

[Andrew Vagin]

On Tue, Nov 13, 2012 at 10:44:32PM +0400, Andrew Vagin wrote:
> 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;
I think all hacks should be in a one place, it is easier for reading.
> > 
> > > +				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
> > 
> > >  	}
> > >  }
> > >  
> > > 
> > 
> >