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-rw-r--r--Documentation/networking/net_cachelines/tcp_sock.rst1
-rw-r--r--include/linux/tcp.h3
-rw-r--r--include/net/tcp.h22
-rw-r--r--net/ipv4/tcp.c2
-rw-r--r--net/ipv4/tcp_fastopen.c1
-rw-r--r--net/ipv4/tcp_input.c11
-rw-r--r--net/ipv4/tcp_minisocks.c1
-rw-r--r--net/ipv4/tcp_output.c3
-rw-r--r--net/mptcp/options.c6
-rw-r--r--tools/testing/selftests/net/packetdrill/tcp_rcv_big_endseq.pkt2
-rw-r--r--tools/testing/selftests/net/packetdrill/tcp_rcv_neg_window.pkt26
-rw-r--r--tools/testing/selftests/net/packetdrill/tcp_rcv_wnd_shrink_allowed.pkt40
-rw-r--r--tools/testing/selftests/net/packetdrill/tcp_rcv_wnd_shrink_nomem.pkt132
13 files changed, 242 insertions, 8 deletions
diff --git a/Documentation/networking/net_cachelines/tcp_sock.rst b/Documentation/networking/net_cachelines/tcp_sock.rst
index 563daea10d6c..fecf61166a54 100644
--- a/Documentation/networking/net_cachelines/tcp_sock.rst
+++ b/Documentation/networking/net_cachelines/tcp_sock.rst
@@ -121,6 +121,7 @@ u64 delivered_mstamp read_write
u32 rate_delivered read_mostly tcp_rate_gen
u32 rate_interval_us read_mostly rate_delivered,rate_app_limited
u32 rcv_wnd read_write read_mostly tcp_select_window,tcp_receive_window,tcp_fast_path_check
+u32 rcv_mwnd_seq read_write tcp_select_window
u32 write_seq read_write tcp_rate_check_app_limited,tcp_write_queue_empty,tcp_skb_entail,forced_push,tcp_mark_push
u32 notsent_lowat read_mostly tcp_stream_memory_free
u32 pushed_seq read_write tcp_mark_push,forced_push
diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index bcebc4f07532..6982f10e826b 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -316,6 +316,9 @@ struct tcp_sock {
*/
u32 app_limited; /* limited until "delivered" reaches this val */
u32 rcv_wnd; /* Current receiver window */
+ u32 rcv_mwnd_seq; /* Maximum window sequence number (RFC 7323,
+ * section 2.4, receiver requirements)
+ */
u32 rcv_tstamp; /* timestamp of last received ACK (for keepalives) */
/*
* Options received (usually on last packet, some only on SYN packets).
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 48dffcca0a71..f87bdacb5a69 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -934,6 +934,28 @@ static inline u32 tcp_receive_window(const struct tcp_sock *tp)
return (u32) win;
}
+/* Compute the maximum receive window we ever advertised.
+ * Rcv_nxt can be after the window if our peer push more data
+ * than the offered window.
+ */
+static inline u32 tcp_max_receive_window(const struct tcp_sock *tp)
+{
+ s32 win = tp->rcv_mwnd_seq - tp->rcv_nxt;
+
+ if (win < 0)
+ win = 0;
+ return (u32) win;
+}
+
+/* Check if we need to update the maximum receive window sequence number */
+static inline void tcp_update_max_rcv_wnd_seq(struct tcp_sock *tp)
+{
+ u32 wre = tp->rcv_wup + tp->rcv_wnd;
+
+ if (after(wre, tp->rcv_mwnd_seq))
+ tp->rcv_mwnd_seq = wre;
+}
+
/* Choose a new window, without checks for shrinking, and without
* scaling applied to the result. The caller does these things
* if necessary. This is a "raw" window selection.
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index ed6f6712f060..516087c622ad 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3561,6 +3561,7 @@ static int tcp_repair_set_window(struct tcp_sock *tp, sockptr_t optbuf, int len)
tp->rcv_wnd = opt.rcv_wnd;
tp->rcv_wup = opt.rcv_wup;
+ tp->rcv_mwnd_seq = opt.rcv_wup + opt.rcv_wnd;
return 0;
}
@@ -5275,6 +5276,7 @@ static void __init tcp_struct_check(void)
CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_txrx, received_ecn_bytes);
CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_txrx, app_limited);
CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_txrx, rcv_wnd);
+ CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_txrx, rcv_mwnd_seq);
CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_txrx, rcv_tstamp);
CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_txrx, rx_opt);
diff --git a/net/ipv4/tcp_fastopen.c b/net/ipv4/tcp_fastopen.c
index 9fdc19accafd..4e389d609f91 100644
--- a/net/ipv4/tcp_fastopen.c
+++ b/net/ipv4/tcp_fastopen.c
@@ -377,6 +377,7 @@ static struct sock *tcp_fastopen_create_child(struct sock *sk,
tcp_rsk(req)->rcv_nxt = tp->rcv_nxt;
tp->rcv_wup = tp->rcv_nxt;
+ tp->rcv_mwnd_seq = tp->rcv_wup + tp->rcv_wnd;
/* tcp_conn_request() is sending the SYNACK,
* and queues the child into listener accept queue.
*/
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 71ac69b7b75e..e6b2f4be7723 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -4808,20 +4808,18 @@ static enum skb_drop_reason tcp_sequence(const struct sock *sk,
const struct tcphdr *th)
{
const struct tcp_sock *tp = tcp_sk(sk);
- u32 seq_limit;
if (before(end_seq, tp->rcv_wup))
return SKB_DROP_REASON_TCP_OLD_SEQUENCE;
- seq_limit = tp->rcv_nxt + tcp_receive_window(tp);
- if (unlikely(after(end_seq, seq_limit))) {
+ if (unlikely(after(end_seq, tp->rcv_nxt + tcp_max_receive_window(tp)))) {
/* Some stacks are known to handle FIN incorrectly; allow the
* FIN to extend beyond the window and check it in detail later.
*/
- if (!after(end_seq - th->fin, seq_limit))
+ if (!after(end_seq - th->fin, tp->rcv_nxt + tcp_receive_window(tp)))
return SKB_NOT_DROPPED_YET;
- if (after(seq, seq_limit))
+ if (after(seq, tp->rcv_nxt + tcp_max_receive_window(tp)))
return SKB_DROP_REASON_TCP_INVALID_SEQUENCE;
/* Only accept this packet if receive queue is empty. */
@@ -5680,6 +5678,7 @@ drop:
if (!before(TCP_SKB_CB(skb)->seq,
tp->rcv_nxt + tcp_receive_window(tp))) {
reason = SKB_DROP_REASON_TCP_OVERWINDOW;
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_BEYOND_WINDOW);
goto out_of_window;
}
@@ -6903,6 +6902,7 @@ consume:
*/
WRITE_ONCE(tp->rcv_nxt, TCP_SKB_CB(skb)->seq + 1);
tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
+ tp->rcv_mwnd_seq = tp->rcv_wup + tp->rcv_wnd;
/* RFC1323: The window in SYN & SYN/ACK segments is
* never scaled.
@@ -7015,6 +7015,7 @@ consume:
WRITE_ONCE(tp->rcv_nxt, TCP_SKB_CB(skb)->seq + 1);
WRITE_ONCE(tp->copied_seq, tp->rcv_nxt);
tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
+ tp->rcv_mwnd_seq = tp->rcv_wup + tp->rcv_wnd;
/* RFC1323: The window in SYN & SYN/ACK segments is
* never scaled.
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index dafb63b923d0..d350d794a959 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -604,6 +604,7 @@ struct sock *tcp_create_openreq_child(const struct sock *sk,
newtp->window_clamp = req->rsk_window_clamp;
newtp->rcv_ssthresh = req->rsk_rcv_wnd;
newtp->rcv_wnd = req->rsk_rcv_wnd;
+ newtp->rcv_mwnd_seq = newtp->rcv_wup + req->rsk_rcv_wnd;
newtp->rx_opt.wscale_ok = ireq->wscale_ok;
if (newtp->rx_opt.wscale_ok) {
newtp->rx_opt.snd_wscale = ireq->snd_wscale;
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 34a25ef61006..35c3b0ab5a0c 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -293,6 +293,7 @@ static u16 tcp_select_window(struct sock *sk)
tp->pred_flags = 0;
tp->rcv_wnd = 0;
tp->rcv_wup = tp->rcv_nxt;
+ tcp_update_max_rcv_wnd_seq(tp);
return 0;
}
@@ -316,6 +317,7 @@ static u16 tcp_select_window(struct sock *sk)
tp->rcv_wnd = new_win;
tp->rcv_wup = tp->rcv_nxt;
+ tcp_update_max_rcv_wnd_seq(tp);
/* Make sure we do not exceed the maximum possible
* scaled window.
@@ -4165,6 +4167,7 @@ static void tcp_connect_init(struct sock *sk)
else
tp->rcv_tstamp = tcp_jiffies32;
tp->rcv_wup = tp->rcv_nxt;
+ tp->rcv_mwnd_seq = tp->rcv_nxt + tp->rcv_wnd;
WRITE_ONCE(tp->copied_seq, tp->rcv_nxt);
inet_csk(sk)->icsk_rto = tcp_timeout_init(sk);
diff --git a/net/mptcp/options.c b/net/mptcp/options.c
index 43df4293f58b..8a1c5698983c 100644
--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c
@@ -1076,6 +1076,7 @@ static void rwin_update(struct mptcp_sock *msk, struct sock *ssk,
* resync.
*/
tp->rcv_wnd += mptcp_rcv_wnd - subflow->rcv_wnd_sent;
+ tcp_update_max_rcv_wnd_seq(tp);
subflow->rcv_wnd_sent = mptcp_rcv_wnd;
}
@@ -1338,8 +1339,9 @@ raise_win:
*/
rcv_wnd_new = rcv_wnd_old;
win = rcv_wnd_old - ack_seq;
- tp->rcv_wnd = min_t(u64, win, U32_MAX);
- new_win = tp->rcv_wnd;
+ new_win = min_t(u64, win, U32_MAX);
+ tp->rcv_wnd = new_win;
+ tcp_update_max_rcv_wnd_seq(tp);
/* Make sure we do not exceed the maximum possible
* scaled window.
diff --git a/tools/testing/selftests/net/packetdrill/tcp_rcv_big_endseq.pkt b/tools/testing/selftests/net/packetdrill/tcp_rcv_big_endseq.pkt
index 6c0f32c40f19..12882be10f2e 100644
--- a/tools/testing/selftests/net/packetdrill/tcp_rcv_big_endseq.pkt
+++ b/tools/testing/selftests/net/packetdrill/tcp_rcv_big_endseq.pkt
@@ -36,7 +36,7 @@
+0 read(4, ..., 100000) = 4000
-// If queue is empty, accept a packet even if its end_seq is above wup + rcv_wnd
+// If queue is empty, accept a packet even if its end_seq is above rcv_mwnd_seq
+0 < P. 4001:54001(50000) ack 1 win 257
* > . 1:1(0) ack 54001 win 0
diff --git a/tools/testing/selftests/net/packetdrill/tcp_rcv_neg_window.pkt b/tools/testing/selftests/net/packetdrill/tcp_rcv_neg_window.pkt
new file mode 100644
index 000000000000..15a9b4938f16
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_rcv_neg_window.pkt
@@ -0,0 +1,26 @@
+// SPDX-License-Identifier: GPL-2.0
+
+--mss=1000
+
+`./defaults.sh`
+
+// Establish a connection.
+ +0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+ +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
+ +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [20000], 4) = 0
+ +0 bind(3, ..., ...) = 0
+ +0 listen(3, 1) = 0
+
+ +0 < S 0:0(0) win 32792 <mss 1000,nop,wscale 7>
+ +0 > S. 0:0(0) ack 1 win 18980 <mss 1460,nop,wscale 0>
+ +.1 < . 1:1(0) ack 1 win 257
+
+ +0 accept(3, ..., ...) = 4
+
+// A too big packet is accepted if the receive queue is empty
+ +0 < P. 1:20001(20000) ack 1 win 257
+// Send a RST immediately so that there is no rcv_wup/rcv_mwnd_seq update yet
+ +0 < R. 20001:20001(0) ack 1 win 257
+
+ +.1 %{ assert tcpi_state == TCP_CLOSE, tcpi_state }%
+
diff --git a/tools/testing/selftests/net/packetdrill/tcp_rcv_wnd_shrink_allowed.pkt b/tools/testing/selftests/net/packetdrill/tcp_rcv_wnd_shrink_allowed.pkt
new file mode 100644
index 000000000000..6af0e0eb183a
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_rcv_wnd_shrink_allowed.pkt
@@ -0,0 +1,40 @@
+// SPDX-License-Identifier: GPL-2.0
+
+--mss=1000
+
+`./defaults.sh
+sysctl -q net.ipv4.tcp_shrink_window=1
+sysctl -q net.ipv4.tcp_rmem="4096 32768 $((32*1024*1024))"`
+
+ 0 `nstat -n`
+
+// Establish a connection.
+ +0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+ +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
+ +0 bind(3, ..., ...) = 0
+ +0 listen(3, 1) = 0
+
+ +0 < S 0:0(0) win 32792 <mss 1000,nop,wscale 7>
+ +0 > S. 0:0(0) ack 1 <mss 1460,nop,wscale 10>
+ +0 < . 1:1(0) ack 1 win 257
+
+ +0 accept(3, ..., ...) = 4
+
+ +0 < P. 1:10001(10000) ack 1 win 257
+ * > . 1:1(0) ack 10001 win 15
+
+ +0 < P. 10001:11024(1023) ack 1 win 257
+ * > . 1:1(0) ack 11024 win 13
+
+// Max window seq advertised 10001 + 15*1024 = 25361, last advertised: 11024 + 13*1024 = 24336
+
+// Segment beyond the max window is dropped
+ +0 < P. 11024:25362(14338) ack 1 win 257
+ * > . 1:1(0) ack 11024 win 13
+
+// Segment using the max window is accepted
+ +0 < P. 11024:25361(14337) ack 1 win 257
+ * > . 1:1(0) ack 25361 win 0
+
+// Check LINUX_MIB_BEYOND_WINDOW has been incremented once
+ +0 `nstat | grep TcpExtBeyondWindow | grep -q " 1 "`
diff --git a/tools/testing/selftests/net/packetdrill/tcp_rcv_wnd_shrink_nomem.pkt b/tools/testing/selftests/net/packetdrill/tcp_rcv_wnd_shrink_nomem.pkt
new file mode 100644
index 000000000000..a80eb55dc69a
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_rcv_wnd_shrink_nomem.pkt
@@ -0,0 +1,132 @@
+// SPDX-License-Identifier: GPL-2.0
+// When tcp_receive_window() < tcp_max_receive_window(), tcp_sequence() accepts
+// packets that would be dropped under normal conditions (i.e. tcp_receive_window()
+// equal to tcp_max_receive_window()).
+// Test that such packets are handled as expected for RWIN == 0 and for RWIN > 0.
+
+--mss=1000
+
+`./defaults.sh`
+
+ 0 `nstat -n`
+
+// Establish a connection.
+ +0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+ +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
+ +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1000000], 4) = 0
+ +0 bind(3, ..., ...) = 0
+ +0 listen(3, 1) = 0
+
+ +0 < S 0:0(0) win 32792 <mss 1000,nop,nop,sackOK,nop,wscale 7>
+ +0 > S. 0:0(0) ack 1 win 65535 <mss 1460,nop,nop,sackOK,nop,wscale 4>
+ +0 < . 1:1(0) ack 1 win 257
+
+ +0 accept(3, ..., ...) = 4
+
+// Put 1040000 bytes into the receive buffer
+ +0 < P. 1:65001(65000) ack 1 win 257
+ * > . 1:1(0) ack 65001
+ +0 < P. 65001:130001(65000) ack 1 win 257
+ * > . 1:1(0) ack 130001
+ +0 < P. 130001:195001(65000) ack 1 win 257
+ * > . 1:1(0) ack 195001
+ +0 < P. 195001:260001(65000) ack 1 win 257
+ * > . 1:1(0) ack 260001
+ +0 < P. 260001:325001(65000) ack 1 win 257
+ * > . 1:1(0) ack 325001
+ +0 < P. 325001:390001(65000) ack 1 win 257
+ * > . 1:1(0) ack 390001
+ +0 < P. 390001:455001(65000) ack 1 win 257
+ * > . 1:1(0) ack 455001
+ +0 < P. 455001:520001(65000) ack 1 win 257
+ * > . 1:1(0) ack 520001
+ +0 < P. 520001:585001(65000) ack 1 win 257
+ * > . 1:1(0) ack 585001
+ +0 < P. 585001:650001(65000) ack 1 win 257
+ * > . 1:1(0) ack 650001
+ +0 < P. 650001:715001(65000) ack 1 win 257
+ * > . 1:1(0) ack 715001
+ +0 < P. 715001:780001(65000) ack 1 win 257
+ * > . 1:1(0) ack 780001
+ +0 < P. 780001:845001(65000) ack 1 win 257
+ * > . 1:1(0) ack 845001
+ +0 < P. 845001:910001(65000) ack 1 win 257
+ * > . 1:1(0) ack 910001
+ +0 < P. 910001:975001(65000) ack 1 win 257
+ * > . 1:1(0) ack 975001
+ +0 < P. 975001:1040001(65000) ack 1 win 257
+ * > . 1:1(0) ack 1040001
+
+// Trigger an extreme memory squeeze by shrinking SO_RCVBUF
+ +0 setsockopt(4, SOL_SOCKET, SO_RCVBUF, [16000], 4) = 0
+
+ +0 < P. 1040001:1105001(65000) ack 1 win 257
+ * > . 1:1(0) ack 1040001 win 0
+// Check LINUX_MIB_TCPRCVQDROP has been incremented
+ +0 `nstat -s | grep TcpExtTCPRcvQDrop| grep -q " 1 "`
+
+// RWIN == 0: rcv_wup = 1040001, rcv_wnd = 0, rcv_mwnd_seq > 1105001 (significantly larger, typically ~1970000)
+
+// Accept pure ack with seq in max adv. window
+ +0 write(4, ..., 1000) = 1000
+ +0 > P. 1:1001(1000) ack 1040001 win 0
+ +0 < . 1105001:1105001(0) ack 1001 win 257
+
+// In order segment, in max adv. window -> drop (SKB_DROP_REASON_TCP_ZEROWINDOW)
+ +0 < P. 1040001:1041001(1000) ack 1001 win 257
+ +0 > . 1001:1001(0) ack 1040001 win 0
+// Ooo partial segment, in max adv. window -> drop (SKB_DROP_REASON_TCP_ZEROWINDOW)
+ +0 < P. 1039001:1041001(2000) ack 1001 win 257
+ +0 > . 1001:1001(0) ack 1040001 win 0 <nop,nop,sack 1039001:1040001>
+// Check LINUX_MIB_TCPZEROWINDOWDROP has been incremented twice
+ +0 `nstat -s | grep TcpExtTCPZeroWindowDrop| grep -q " 2 "`
+
+// Ooo segment, in max adv. window -> drop (SKB_DROP_REASON_TCP_OVERWINDOW)
+ +0 < P. 1105001:1106001(1000) ack 1001 win 257
+ +0 > . 1001:1001(0) ack 1040001 win 0
+// Ooo segment, beyond max adv. window -> drop (SKB_DROP_REASON_TCP_INVALID_SEQUENCE)
+ +0 < P. 2000001:2001001(1000) ack 1001 win 257
+ +0 > . 1001:1001(0) ack 1040001 win 0
+// Check LINUX_MIB_BEYOND_WINDOW has been incremented twice
+ +0 `nstat -s | grep TcpExtBeyondWindow | grep -q " 2 "`
+
+// Read all data
+ +0 read(4, ..., 2000000) = 1040000
+ * > . 1001:1001(0) ack 1040001
+
+// RWIN > 0: rcv_wup = 1040001, 0 < rcv_wnd < 32000, rcv_mwnd_seq > 1105001 (significantly larger, typically ~1970000)
+
+// Accept pure ack with seq in max adv. window, beyond adv. window
+ +0 write(4, ..., 1000) = 1000
+ +0 > P. 1001:2001(1000) ack 1040001
+ +0 < . 1105001:1105001(0) ack 2001 win 257
+
+// In order segment, in max adv. window, in adv. window -> accept
+// Note: This also ensures that we cannot hit the empty queue exception in tcp_sequence() in the following tests
+ +0 < P. 1040001:1041001(1000) ack 2001 win 257
+ * > . 2001:2001(0) ack 1041001
+
+// Ooo partial segment, in adv. window -> accept
+ +0 < P. 1040001:1042001(2000) ack 2001 win 257
+ +0 > . 2001:2001(0) ack 1042001 <nop,nop,sack 1040001:1041001>
+
+// Ooo segment, in max adv. window, beyond adv. window -> drop (SKB_DROP_REASON_TCP_OVERWINDOW)
+ +0 < P. 1105001:1106001(1000) ack 2001 win 257
+ +0 > . 2001:2001(0) ack 1042001
+// Ooo segment, beyond max adv. window, beyond adv. window -> drop (SKB_DROP_REASON_TCP_INVALID_SEQUENCE)
+ +0 < P. 2000001:2001001(1000) ack 2001 win 257
+ +0 > . 2001:2001(0) ack 1042001
+// Check LINUX_MIB_BEYOND_WINDOW has been incremented twice
+ +0 `nstat -s | grep TcpExtBeyondWindow | grep -q " 4 "`
+
+// We are allowed to go beyond the window and buffer with one packet
+ +0 < P. 1042001:1062001(20000) ack 2001 win 257
+ * > . 2001:2001(0) ack 1062001
+ +0 < P. 1062001:1082001(20000) ack 2001 win 257
+ * > . 2001:2001(0) ack 1082001 win 0
+
+// But not more: In order segment, in max adv. window -> drop (SKB_DROP_REASON_TCP_ZEROWINDOW)
+ +0 < P. 1082001:1083001(1000) ack 2001 win 257
+ * > . 2001:2001(0) ack 1082001
+// Check LINUX_MIB_TCPZEROWINDOWDROP has been incremented again
+ +0 `nstat -s | grep TcpExtTCPZeroWindowDrop| grep -q " 3 "`
generated by cgit v1.2.3 (git 2.39.0) at 2026-05-13 19:59:13 +0300