[PATCH 5.10 169/199] tcp: fix TCP socket rehash stats mis-accounting

Greg Kroah-Hartman
2021-01-26T10:01:29Z

From: Yuchung Cheng <ycheng@google.com>

commit 9c30ae8398b0813e237bde387d67a7f74ab2db2d upstream.

The previous commit 32efcc06d2a1 ("tcp: export count for rehash attempts")
would mis-account rehashing SNMP and socket stats:

a. During handshake of an active open, only counts the first
SYN timeout

b. After handshake of passive and active open, stop updating
after (roughly) TCP_RETRIES1 recurring RTOs

c. After the socket aborts, over count timeout_rehash by 1

This patch fixes this by checking the rehash result from sk_rethink_txhash.

Fixes: 32efcc06d2a1 ("tcp: export count for rehash attempts")
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Link: https://lore.kernel.org/r/20210119192619.1848270-1-ycheng@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
include/net/sock.h | 17 ++++++++++++-----
net/ipv4/tcp_input.c | 5 ++---
net/ipv4/tcp_timer.c | 22 ++++++++--------------
3 files changed, 22 insertions(+), 22 deletions(-)

--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1903,10 +1903,13 @@ static inline void sk_set_txhash(struct
sk->sk_txhash = net_tx_rndhash();
}

-static inline void sk_rethink_txhash(struct sock *sk)
+static inline bool sk_rethink_txhash(struct sock *sk)
{
- if (sk->sk_txhash)
+ if (sk->sk_txhash) {
sk_set_txhash(sk);
+ return true;
+ }
+ return false;
}

static inline struct dst_entry *
@@ -1929,12 +1932,10 @@ sk_dst_get(struct sock *sk)
return dst;
}

-static inline void dst_negative_advice(struct sock *sk)
+static inline void __dst_negative_advice(struct sock *sk)
{
struct dst_entry *ndst, *dst = __sk_dst_get(sk);

- sk_rethink_txhash(sk);
-
if (dst && dst->ops->negative_advice) {
ndst = dst->ops->negative_advice(dst);

@@ -1946,6 +1947,12 @@ static inline void dst_negative_advice(s
}
}

+static inline void dst_negative_advice(struct sock *sk)
+{
+ sk_rethink_txhash(sk);
+ __dst_negative_advice(sk);
+}
+
static inline void
__sk_dst_set(struct sock *sk, struct dst_entry *dst)
{
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -4379,10 +4379,9 @@ static void tcp_rcv_spurious_retrans(str
* The receiver remembers and reflects via DSACKs. Leverage the
* DSACK state and change the txhash to re-route speculatively.
*/
- if (TCP_SKB_CB(skb)->seq == tcp_sk(sk)->duplicate_sack[0].start_seq) {
- sk_rethink_txhash(sk);
+ if (TCP_SKB_CB(skb)->seq == tcp_sk(sk)->duplicate_sack[0].start_seq &&
+ sk_rethink_txhash(sk))
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDUPLICATEDATAREHASH);
- }
}

static void tcp_send_dupack(struct sock *sk, const struct sk_buff *skb)
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -219,14 +219,8 @@ static int tcp_write_timeout(struct sock
int retry_until;

if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
- if (icsk->icsk_retransmits) {
- dst_negative_advice(sk);
- } else {
- sk_rethink_txhash(sk);
- tp->timeout_rehash++;
- __NET_INC_STATS(sock_net(sk),
- LINUX_MIB_TCPTIMEOUTREHASH);
- }
+ if (icsk->icsk_retransmits)
+ __dst_negative_advice(sk);
retry_until = icsk->icsk_syn_retries ? : net->ipv4.sysctl_tcp_syn_retries;
expired = icsk->icsk_retransmits >= retry_until;
} else {
@@ -234,12 +228,7 @@ static int tcp_write_timeout(struct sock
/* Black hole detection */
tcp_mtu_probing(icsk, sk);

- dst_negative_advice(sk);
- } else {
- sk_rethink_txhash(sk);
- tp->timeout_rehash++;
- __NET_INC_STATS(sock_net(sk),
- LINUX_MIB_TCPTIMEOUTREHASH);
+ __dst_negative_advice(sk);
}

retry_until = net->ipv4.sysctl_tcp_retries2;
@@ -270,6 +259,11 @@ static int tcp_write_timeout(struct sock
return 1;
}

+ if (sk_rethink_txhash(sk)) {
+ tp->timeout_rehash++;
+ __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPTIMEOUTREHASH);
+ }
+
return 0;
}