Messages in this thread | | | From | Menglong Dong <> | Date | Mon, 16 May 2022 12:54:53 +0800 | Subject | Re: [PATCH net-next 8/9] net: tcp: add skb drop reasons to tcp tw code path |
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On Mon, May 16, 2022 at 12:22 PM Eric Dumazet <edumazet@google.com> wrote: > > On Sun, May 15, 2022 at 8:46 PM <menglong8.dong@gmail.com> wrote: > > > > From: Menglong Dong <imagedong@tencent.com> > > > > In order to get the reasons of skb drops, add a function argument of > > type 'enum skb_drop_reason *reason' to tcp_timewait_state_process(). > > > > In the origin code, all packets to time-wait socket are treated as > > dropping with kfree_skb(), which can make users confused. Therefore, > > we use consume_skb() for the skbs that are 'good'. We can check the > > value of 'reason' to decide use kfree_skb() or consume_skb(). > > > > The new reason 'TIMEWAIT' is added for the case that the skb is dropped > > as the socket in time-wait state. > > > > Signed-off-by: Menglong Dong <imagedong@tencent.com> > > --- > > include/linux/skbuff.h | 5 +++++ > > include/net/tcp.h | 7 ++++--- > > net/ipv4/tcp_ipv4.c | 11 +++++++++-- > > net/ipv4/tcp_minisocks.c | 24 ++++++++++++++++++++---- > > net/ipv6/tcp_ipv6.c | 10 ++++++++-- > > 5 files changed, 46 insertions(+), 11 deletions(-) > > > > diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h > > index 4578bbab5a3e..8d18fc5a5af6 100644 > > --- a/include/linux/skbuff.h > > +++ b/include/linux/skbuff.h > > @@ -560,6 +560,10 @@ struct sk_buff; > > * SKB_DROP_REASON_TCP_REQQFULLDROP > > * request queue of the listen socket is full, corresponding to > > * LINUX_MIB_TCPREQQFULLDROP > > + * > > + * SKB_DROP_REASON_TIMEWAIT > > + * socket is in time-wait state and all packet that received will > > + * be treated as 'drop', except a good 'SYN' packet > > */ > > #define __DEFINE_SKB_DROP_REASON(FN) \ > > FN(NOT_SPECIFIED) \ > > @@ -631,6 +635,7 @@ struct sk_buff; > > FN(TCP_ABORTONDATA) \ > > FN(LISTENOVERFLOWS) \ > > FN(TCP_REQQFULLDROP) \ > > + FN(TIMEWAIT) \ > > FN(MAX) > > > > /* The reason of skb drop, which is used in kfree_skb_reason(). > > diff --git a/include/net/tcp.h b/include/net/tcp.h > > index 082dd0627e2e..88217b8d95ac 100644 > > --- a/include/net/tcp.h > > +++ b/include/net/tcp.h > > @@ -380,9 +380,10 @@ enum tcp_tw_status { > > }; > > > > > > -enum tcp_tw_status tcp_timewait_state_process(struct inet_timewait_sock *tw, > > - struct sk_buff *skb, > > - const struct tcphdr *th); > > +enum tcp_tw_status > > +tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb, > > + const struct tcphdr *th, > > + enum skb_drop_reason *reason); > > struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb, > > struct request_sock *req, bool fastopen, > > bool *lost_race); > > diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c > > index 708f92b03f42..9174ee162633 100644 > > --- a/net/ipv4/tcp_ipv4.c > > +++ b/net/ipv4/tcp_ipv4.c > > @@ -2134,7 +2134,8 @@ int tcp_v4_rcv(struct sk_buff *skb) > > inet_twsk_put(inet_twsk(sk)); > > goto csum_error; > > } > > - switch (tcp_timewait_state_process(inet_twsk(sk), skb, th)) { > > + switch (tcp_timewait_state_process(inet_twsk(sk), skb, th, > > + &drop_reason)) { > > case TCP_TW_SYN: { > > struct sock *sk2 = inet_lookup_listener(dev_net(skb->dev), > > &tcp_hashinfo, skb, > > @@ -2150,12 +2151,18 @@ int tcp_v4_rcv(struct sk_buff *skb) > > refcounted = false; > > goto process; > > } > > + /* TCP_FLAGS or NO_SOCKET? */ > > + SKB_DR_SET(drop_reason, TCP_FLAGS); > > } > > /* to ACK */ > > fallthrough; > > case TCP_TW_ACK: > > tcp_v4_timewait_ack(sk, skb); > > - break; > > + refcounted = false; > > + if (drop_reason) > > + goto discard_it; > > + else > > + goto put_and_return; > > case TCP_TW_RST: > > tcp_v4_send_reset(sk, skb); > > inet_twsk_deschedule_put(inet_twsk(sk)); > > diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c > > index 1a21018f6f64..329724118b7f 100644 > > --- a/net/ipv4/tcp_minisocks.c > > +++ b/net/ipv4/tcp_minisocks.c > > @@ -83,13 +83,15 @@ tcp_timewait_check_oow_rate_limit(struct inet_timewait_sock *tw, > > */ > > enum tcp_tw_status > > tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb, > > - const struct tcphdr *th) > > + const struct tcphdr *th, > > + enum skb_drop_reason *reason) > > { > > struct tcp_options_received tmp_opt; > > struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); > > bool paws_reject = false; > > > > tmp_opt.saw_tstamp = 0; > > + *reason = SKB_DROP_REASON_NOT_SPECIFIED; > > if (th->doff > (sizeof(*th) >> 2) && tcptw->tw_ts_recent_stamp) { > > tcp_parse_options(twsk_net(tw), skb, &tmp_opt, 0, NULL); > > > > @@ -113,11 +115,16 @@ tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb, > > return tcp_timewait_check_oow_rate_limit( > > tw, skb, LINUX_MIB_TCPACKSKIPPEDFINWAIT2); > > > > - if (th->rst) > > + if (th->rst) { > > + SKB_DR_SET(*reason, TCP_RESET); > > goto kill; > > + } > > > > - if (th->syn && !before(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt)) > > + if (th->syn && !before(TCP_SKB_CB(skb)->seq, > > + tcptw->tw_rcv_nxt)) { > > + SKB_DR_SET(*reason, TCP_FLAGS); > > return TCP_TW_RST; > > + } > > > > /* Dup ACK? */ > > if (!th->ack || > > @@ -143,6 +150,9 @@ tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb, > > } > > > > inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); > > + > > + /* skb should be free normally on this case. */ > > + *reason = SKB_NOT_DROPPED_YET; > > return TCP_TW_ACK; > > } > > > > @@ -174,6 +184,7 @@ tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb, > > * protocol bug yet. > > */ > > if (twsk_net(tw)->ipv4.sysctl_tcp_rfc1337 == 0) { > > + SKB_DR_SET(*reason, TCP_RESET); > > kill: > > inet_twsk_deschedule_put(tw); > > return TCP_TW_SUCCESS; > > @@ -216,11 +227,14 @@ tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb, > > if (isn == 0) > > isn++; > > TCP_SKB_CB(skb)->tcp_tw_isn = isn; > > + *reason = SKB_NOT_DROPPED_YET; > > return TCP_TW_SYN; > > } > > > > - if (paws_reject) > > + if (paws_reject) { > > + SKB_DR_SET(*reason, TCP_RFC7323_PAWS); > > __NET_INC_STATS(twsk_net(tw), LINUX_MIB_PAWSESTABREJECTED); > > + } > > > > if (!th->rst) { > > /* In this case we must reset the TIMEWAIT timer. > > @@ -232,9 +246,11 @@ tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb, > > if (paws_reject || th->ack) > > inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); > > > > + SKB_DR_OR(*reason, TIMEWAIT); > > return tcp_timewait_check_oow_rate_limit( > > tw, skb, LINUX_MIB_TCPACKSKIPPEDTIMEWAIT); > > } > > + SKB_DR_SET(*reason, TCP_RESET); > > inet_twsk_put(tw); > > return TCP_TW_SUCCESS; > > } > > diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c > > index 27c51991bd54..5c777006de3d 100644 > > --- a/net/ipv6/tcp_ipv6.c > > +++ b/net/ipv6/tcp_ipv6.c > > @@ -1795,7 +1795,8 @@ INDIRECT_CALLABLE_SCOPE int tcp_v6_rcv(struct sk_buff *skb) > > goto csum_error; > > } > > > > - switch (tcp_timewait_state_process(inet_twsk(sk), skb, th)) { > > + switch (tcp_timewait_state_process(inet_twsk(sk), skb, th, > > + &drop_reason)) { > > case TCP_TW_SYN: > > { > > struct sock *sk2; > > @@ -1815,12 +1816,17 @@ INDIRECT_CALLABLE_SCOPE int tcp_v6_rcv(struct sk_buff *skb) > > refcounted = false; > > goto process; > > } > > + SKB_DR_SET(drop_reason, TCP_FLAGS); > > } > > /* to ACK */ > > fallthrough; > > case TCP_TW_ACK: > > tcp_v6_timewait_ack(sk, skb); > > - break; > > + refcounted = false; > > + if (drop_reason) > > + goto discard_it; > > + else > > + goto put_and_return; > > My brain exploded. > I guarantee you that whoever is going to look at this code in one year > will be completely lost. > Adding so much complexity is crazy. >
Yeah, I'm almost lost while adding this code.
> About: refcounted = false ; > > This is not going to be used id "goto discard_it;" is taken. > > If the "goto put_and_return;" is taken, this boils down to: > > return ret ? -1 : 0; > > Are you sure ret is even initialized at this point ? >
About this part, it seems it's my mistake. The correct code should be:
case TCP_TW_ACK: tcp_v6_timewait_ack(sk, skb); - break; + if (drop_reason) { + goto discard_it; + } else { + consume_skb(skb); /* free skb here */ + return 0; + }
As you said, it's a little complex.
> Why are we doing this ? We were doing "return 0;" > > Also, where is skb freed ? > > Are you calling tcp_v6_timewait_ack(sk, skb) after skb has been freed ??? > >
> > > > case TCP_TW_RST: > > tcp_v6_send_reset(sk, skb); > > inet_twsk_deschedule_put(inet_twsk(sk)); > > -- > > 2.36.1 > >
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