tcp: shortcut listeners in tcp_get_info()

Being lockless in tcp_get_info() is hard, because we need to add
specific synchronization in TCP fast path, like seqcount.

Following patch will change inet_diag_dump_icsk() to no longer
hold any lock for non listeners, so that we can properly acquire
socket lock in get_tcp_info() and let it return more consistent counters.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 3251fe71f39f2395befb0e662ca19423e6b9ea90..117982be0caba6a046acbfb11128c42af716891f 100644 (file)
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2721,6 +2721,27 @@ void tcp_get_info(struct sock *sk, struct tcp_info *info)
 
        info->tcpi_state = sk_state_load(sk);
 
+       /* Report meaningful fields for all TCP states, including listeners */
+       rate = READ_ONCE(sk->sk_pacing_rate);
+       rate64 = rate != ~0U ? rate : ~0ULL;
+       put_unaligned(rate64, &info->tcpi_pacing_rate);
+
+       rate = READ_ONCE(sk->sk_max_pacing_rate);
+       rate64 = rate != ~0U ? rate : ~0ULL;
+       put_unaligned(rate64, &info->tcpi_max_pacing_rate);
+
+       info->tcpi_reordering = tp->reordering;
+       info->tcpi_snd_cwnd = tp->snd_cwnd;
+
+       if (info->tcpi_state == TCP_LISTEN) {
+               /* listeners aliased fields :
+                * tcpi_unacked -> Number of children ready for accept()
+                * tcpi_sacked  -> max backlog
+                */
+               info->tcpi_unacked = sk->sk_ack_backlog;
+               info->tcpi_sacked = sk->sk_max_ack_backlog;
+               return;
+       }
        info->tcpi_ca_state = icsk->icsk_ca_state;
        info->tcpi_retransmits = icsk->icsk_retransmits;
        info->tcpi_probes = icsk->icsk_probes_out;
@@ -2748,13 +2769,9 @@ void tcp_get_info(struct sock *sk, struct tcp_info *info)
        info->tcpi_snd_mss = tp->mss_cache;
        info->tcpi_rcv_mss = icsk->icsk_ack.rcv_mss;
 
-       if (info->tcpi_state == TCP_LISTEN) {
-               info->tcpi_unacked = sk->sk_ack_backlog;
-               info->tcpi_sacked = sk->sk_max_ack_backlog;
-       } else {
-               info->tcpi_unacked = tp->packets_out;
-               info->tcpi_sacked = tp->sacked_out;
-       }
+       info->tcpi_unacked = tp->packets_out;
+       info->tcpi_sacked = tp->sacked_out;
+
        info->tcpi_lost = tp->lost_out;
        info->tcpi_retrans = tp->retrans_out;
        info->tcpi_fackets = tp->fackets_out;
@@ -2768,23 +2785,13 @@ void tcp_get_info(struct sock *sk, struct tcp_info *info)
        info->tcpi_rtt = tp->srtt_us >> 3;
        info->tcpi_rttvar = tp->mdev_us >> 2;
        info->tcpi_snd_ssthresh = tp->snd_ssthresh;
-       info->tcpi_snd_cwnd = tp->snd_cwnd;
        info->tcpi_advmss = tp->advmss;
-       info->tcpi_reordering = tp->reordering;
 
        info->tcpi_rcv_rtt = jiffies_to_usecs(tp->rcv_rtt_est.rtt)>>3;
        info->tcpi_rcv_space = tp->rcvq_space.space;
 
        info->tcpi_total_retrans = tp->total_retrans;
 
-       rate = READ_ONCE(sk->sk_pacing_rate);
-       rate64 = rate != ~0U ? rate : ~0ULL;
-       put_unaligned(rate64, &info->tcpi_pacing_rate);
-
-       rate = READ_ONCE(sk->sk_max_pacing_rate);
-       rate64 = rate != ~0U ? rate : ~0ULL;
-       put_unaligned(rate64, &info->tcpi_max_pacing_rate);
-
        do {
                start = u64_stats_fetch_begin_irq(&tp->syncp);
                put_unaligned(tp->bytes_acked, &info->tcpi_bytes_acked);