Skip to content

Commit

Permalink
tcp: better retrans tracking for defer-accept
Browse files Browse the repository at this point in the history
For passive TCP connections using TCP_DEFER_ACCEPT facility,
we incorrectly increment req->retrans each time timeout triggers
while no SYNACK is sent.

SYNACK are not sent for TCP_DEFER_ACCEPT that were established (for
which we received the ACK from client). Only the last SYNACK is sent
so that we can receive again an ACK from client, to move the req into
accept queue. We plan to change this later to avoid the useless
retransmit (and potential problem as this SYNACK could be lost)

TCP_INFO later gives wrong information to user, claiming imaginary
retransmits.

Decouple req->retrans field into two independent fields :

num_retrans : number of retransmit
num_timeout : number of timeouts

num_timeout is the counter that is incremented at each timeout,
regardless of actual SYNACK being sent or not, and used to
compute the exponential timeout.

Introduce inet_rtx_syn_ack() helper to increment num_retrans
only if ->rtx_syn_ack() succeeded.

Use inet_rtx_syn_ack() from tcp_check_req() to increment num_retrans
when we re-send a SYNACK in answer to a (retransmitted) SYN.
Prior to this patch, we were not counting these retransmits.

Change tcp_v[46]_rtx_synack() to increment TCP_MIB_RETRANSSEGS
only if a synack packet was successfully queued.

Reported-by: Yuchung Cheng <[email protected]>
Signed-off-by: Eric Dumazet <[email protected]>
Cc: Julian Anastasov <[email protected]>
Cc: Vijay Subramanian <[email protected]>
Cc: Elliott Hughes <[email protected]>
Cc: Neal Cardwell <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
  • Loading branch information
Eric Dumazet authored and davem330 committed Nov 3, 2012
1 parent 25b1e67 commit e6c022a
Show file tree
Hide file tree
Showing 11 changed files with 56 additions and 35 deletions.
12 changes: 8 additions & 4 deletions include/net/request_sock.h
Original file line number Diff line number Diff line change
Expand Up @@ -49,13 +49,16 @@ struct request_sock_ops {
struct request_sock *req);
};

extern int inet_rtx_syn_ack(struct sock *parent, struct request_sock *req);

/* struct request_sock - mini sock to represent a connection request
*/
struct request_sock {
struct request_sock *dl_next; /* Must be first member! */
u16 mss;
u8 retrans;
u8 cookie_ts; /* syncookie: encode tcpopts in timestamp */
u8 num_retrans; /* number of retransmits */
u8 cookie_ts:1; /* syncookie: encode tcpopts in timestamp */
u8 num_timeout:7; /* number of timeouts */
/* The following two fields can be easily recomputed I think -AK */
u32 window_clamp; /* window clamp at creation time */
u32 rcv_wnd; /* rcv_wnd offered first time */
Expand Down Expand Up @@ -231,7 +234,7 @@ static inline int reqsk_queue_removed(struct request_sock_queue *queue,
{
struct listen_sock *lopt = queue->listen_opt;

if (req->retrans == 0)
if (req->num_timeout == 0)
--lopt->qlen_young;

return --lopt->qlen;
Expand Down Expand Up @@ -269,7 +272,8 @@ static inline void reqsk_queue_hash_req(struct request_sock_queue *queue,
struct listen_sock *lopt = queue->listen_opt;

req->expires = jiffies + timeout;
req->retrans = 0;
req->num_retrans = 0;
req->num_timeout = 0;
req->sk = NULL;
req->dl_next = lopt->syn_table[hash];

Expand Down
3 changes: 1 addition & 2 deletions net/dccp/minisocks.c
Original file line number Diff line number Diff line change
Expand Up @@ -174,8 +174,7 @@ struct sock *dccp_check_req(struct sock *sk, struct sk_buff *skb,
* To protect against Request floods, increment retrans
* counter (backoff, monitored by dccp_response_timer).
*/
req->retrans++;
req->rsk_ops->rtx_syn_ack(sk, req, NULL);
inet_rtx_syn_ack(sk, req);
}
/* Network Duplicate, discard packet */
return NULL;
Expand Down
25 changes: 18 additions & 7 deletions net/ipv4/inet_connection_sock.c
Original file line number Diff line number Diff line change
Expand Up @@ -521,21 +521,31 @@ static inline void syn_ack_recalc(struct request_sock *req, const int thresh,
int *expire, int *resend)
{
if (!rskq_defer_accept) {
*expire = req->retrans >= thresh;
*expire = req->num_timeout >= thresh;
*resend = 1;
return;
}
*expire = req->retrans >= thresh &&
(!inet_rsk(req)->acked || req->retrans >= max_retries);
*expire = req->num_timeout >= thresh &&
(!inet_rsk(req)->acked || req->num_timeout >= max_retries);
/*
* Do not resend while waiting for data after ACK,
* start to resend on end of deferring period to give
* last chance for data or ACK to create established socket.
*/
*resend = !inet_rsk(req)->acked ||
req->retrans >= rskq_defer_accept - 1;
req->num_timeout >= rskq_defer_accept - 1;
}

int inet_rtx_syn_ack(struct sock *parent, struct request_sock *req)
{
int err = req->rsk_ops->rtx_syn_ack(parent, req, NULL);

if (!err)
req->num_retrans++;
return err;
}
EXPORT_SYMBOL(inet_rtx_syn_ack);

void inet_csk_reqsk_queue_prune(struct sock *parent,
const unsigned long interval,
const unsigned long timeout,
Expand Down Expand Up @@ -599,13 +609,14 @@ void inet_csk_reqsk_queue_prune(struct sock *parent,
req->rsk_ops->syn_ack_timeout(parent, req);
if (!expire &&
(!resend ||
!req->rsk_ops->rtx_syn_ack(parent, req, NULL) ||
!inet_rtx_syn_ack(parent, req) ||
inet_rsk(req)->acked)) {
unsigned long timeo;

if (req->retrans++ == 0)
if (req->num_timeout++ == 0)
lopt->qlen_young--;
timeo = min((timeout << req->retrans), max_rto);
timeo = min(timeout << req->num_timeout,
max_rto);
req->expires = now + timeo;
reqp = &req->dl_next;
continue;
Expand Down
2 changes: 1 addition & 1 deletion net/ipv4/inet_diag.c
Original file line number Diff line number Diff line change
Expand Up @@ -620,7 +620,7 @@ static int inet_diag_fill_req(struct sk_buff *skb, struct sock *sk,
r->idiag_family = sk->sk_family;
r->idiag_state = TCP_SYN_RECV;
r->idiag_timer = 1;
r->idiag_retrans = req->retrans;
r->idiag_retrans = req->num_retrans;

r->id.idiag_if = sk->sk_bound_dev_if;
sock_diag_save_cookie(req, r->id.idiag_cookie);
Expand Down
2 changes: 1 addition & 1 deletion net/ipv4/syncookies.c
Original file line number Diff line number Diff line change
Expand Up @@ -340,7 +340,7 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb,
}

req->expires = 0UL;
req->retrans = 0;
req->num_retrans = 0;

/*
* We need to lookup the route here to get at the correct
Expand Down
2 changes: 1 addition & 1 deletion net/ipv4/tcp_input.c
Original file line number Diff line number Diff line change
Expand Up @@ -5991,7 +5991,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
*/
if (req) {
tcp_synack_rtt_meas(sk, req);
tp->total_retrans = req->retrans;
tp->total_retrans = req->num_retrans;

reqsk_fastopen_remove(sk, req, false);
} else {
Expand Down
16 changes: 10 additions & 6 deletions net/ipv4/tcp_ipv4.c
Original file line number Diff line number Diff line change
Expand Up @@ -877,10 +877,13 @@ static int tcp_v4_send_synack(struct sock *sk, struct dst_entry *dst,
}

static int tcp_v4_rtx_synack(struct sock *sk, struct request_sock *req,
struct request_values *rvp)
struct request_values *rvp)
{
TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_RETRANSSEGS);
return tcp_v4_send_synack(sk, NULL, req, rvp, 0, false);
int res = tcp_v4_send_synack(sk, NULL, req, rvp, 0, false);

if (!res)
TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_RETRANSSEGS);
return res;
}

/*
Expand Down Expand Up @@ -1386,7 +1389,8 @@ static int tcp_v4_conn_req_fastopen(struct sock *sk,
struct sock *child;
int err;

req->retrans = 0;
req->num_retrans = 0;
req->num_timeout = 0;
req->sk = NULL;

child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL);
Expand Down Expand Up @@ -1740,7 +1744,7 @@ struct sock *tcp_v4_syn_recv_sock(struct sock *sk, struct sk_buff *skb,

tcp_initialize_rcv_mss(newsk);
tcp_synack_rtt_meas(newsk, req);
newtp->total_retrans = req->retrans;
newtp->total_retrans = req->num_retrans;

#ifdef CONFIG_TCP_MD5SIG
/* Copy over the MD5 key from the original socket */
Expand Down Expand Up @@ -2638,7 +2642,7 @@ static void get_openreq4(const struct sock *sk, const struct request_sock *req,
0, 0, /* could print option size, but that is af dependent. */
1, /* timers active (only the expire timer) */
jiffies_delta_to_clock_t(delta),
req->retrans,
req->num_timeout,
from_kuid_munged(seq_user_ns(f), uid),
0, /* non standard timer */
0, /* open_requests have no inode */
Expand Down
8 changes: 4 additions & 4 deletions net/ipv4/tcp_minisocks.c
Original file line number Diff line number Diff line change
Expand Up @@ -552,7 +552,7 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
* it can be estimated (approximately)
* from another data.
*/
tmp_opt.ts_recent_stamp = get_seconds() - ((TCP_TIMEOUT_INIT/HZ)<<req->retrans);
tmp_opt.ts_recent_stamp = get_seconds() - ((TCP_TIMEOUT_INIT/HZ)<<req->num_timeout);
paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
}
}
Expand Down Expand Up @@ -581,7 +581,7 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
* Note that even if there is new data in the SYN packet
* they will be thrown away too.
*/
req->rsk_ops->rtx_syn_ack(sk, req, NULL);
inet_rtx_syn_ack(sk, req);
return NULL;
}

Expand Down Expand Up @@ -695,7 +695,7 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
/* Got ACK for our SYNACK, so update baseline for SYNACK RTT sample. */
if (tmp_opt.saw_tstamp && tmp_opt.rcv_tsecr)
tcp_rsk(req)->snt_synack = tmp_opt.rcv_tsecr;
else if (req->retrans) /* don't take RTT sample if retrans && ~TS */
else if (req->num_retrans) /* don't take RTT sample if retrans && ~TS */
tcp_rsk(req)->snt_synack = 0;

/* For Fast Open no more processing is needed (sk is the
Expand All @@ -705,7 +705,7 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
return sk;

/* While TCP_DEFER_ACCEPT is active, drop bare ACK. */
if (req->retrans < inet_csk(sk)->icsk_accept_queue.rskq_defer_accept &&
if (req->num_timeout < inet_csk(sk)->icsk_accept_queue.rskq_defer_accept &&
TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) {
inet_rsk(req)->acked = 1;
NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP);
Expand Down
8 changes: 4 additions & 4 deletions net/ipv4/tcp_timer.c
Original file line number Diff line number Diff line change
Expand Up @@ -318,7 +318,7 @@ static void tcp_fastopen_synack_timer(struct sock *sk)
req = tcp_sk(sk)->fastopen_rsk;
req->rsk_ops->syn_ack_timeout(sk, req);

if (req->retrans >= max_retries) {
if (req->num_timeout >= max_retries) {
tcp_write_err(sk);
return;
}
Expand All @@ -327,10 +327,10 @@ static void tcp_fastopen_synack_timer(struct sock *sk)
* regular retransmit because if the child socket has been accepted
* it's not good to give up too easily.
*/
req->rsk_ops->rtx_syn_ack(sk, req, NULL);
req->retrans++;
inet_rtx_syn_ack(sk, req);
req->num_timeout++;
inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
TCP_TIMEOUT_INIT << req->retrans, TCP_RTO_MAX);
TCP_TIMEOUT_INIT << req->num_timeout, TCP_RTO_MAX);
}

/*
Expand Down
2 changes: 1 addition & 1 deletion net/ipv6/syncookies.c
Original file line number Diff line number Diff line change
Expand Up @@ -214,7 +214,7 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
ireq6->iif = inet6_iif(skb);

req->expires = 0UL;
req->retrans = 0;
req->num_retrans = 0;
ireq->ecn_ok = ecn_ok;
ireq->snd_wscale = tcp_opt.snd_wscale;
ireq->sack_ok = tcp_opt.sack_ok;
Expand Down
11 changes: 7 additions & 4 deletions net/ipv6/tcp_ipv6.c
Original file line number Diff line number Diff line change
Expand Up @@ -495,9 +495,12 @@ static int tcp_v6_rtx_synack(struct sock *sk, struct request_sock *req,
struct request_values *rvp)
{
struct flowi6 fl6;
int res;

TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_RETRANSSEGS);
return tcp_v6_send_synack(sk, NULL, &fl6, req, rvp, 0);
res = tcp_v6_send_synack(sk, NULL, &fl6, req, rvp, 0);
if (!res)
TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_RETRANSSEGS);
return res;
}

static void tcp_v6_reqsk_destructor(struct request_sock *req)
Expand Down Expand Up @@ -1364,7 +1367,7 @@ static struct sock * tcp_v6_syn_recv_sock(struct sock *sk, struct sk_buff *skb,

tcp_initialize_rcv_mss(newsk);
tcp_synack_rtt_meas(newsk, req);
newtp->total_retrans = req->retrans;
newtp->total_retrans = req->num_retrans;

newinet->inet_daddr = newinet->inet_saddr = LOOPBACK4_IPV6;
newinet->inet_rcv_saddr = LOOPBACK4_IPV6;
Expand Down Expand Up @@ -1866,7 +1869,7 @@ static void get_openreq6(struct seq_file *seq,
0,0, /* could print option size, but that is af dependent. */
1, /* timers active (only the expire timer) */
jiffies_to_clock_t(ttd),
req->retrans,
req->num_timeout,
from_kuid_munged(seq_user_ns(seq), uid),
0, /* non standard timer */
0, /* open_requests have no inode */
Expand Down

0 comments on commit e6c022a

Please sign in to comment.