[PATCH] tcp: don't use timestamp from repaired skb-s to calculate RTT (v2)
From: Andrey Vagin
Date: Wed Aug 13 2014 - 08:03:43 EST
We don't know right timestamp for repaired skb-s. Wrong RTT estimations
isn't good, because some congestion modules heavily depends on it.
This patch adds the TCPCB_REPAIRED flag, which is included in
TCPCB_RETRANS.
Thanks to Eric for the advice how to fix this issue.
This patch fixes the warning:
[ 879.562947] WARNING: CPU: 0 PID: 2825 at net/ipv4/tcp_input.c:3078 tcp_ack+0x11f5/0x1380()
[ 879.567253] CPU: 0 PID: 2825 Comm: socket-tcpbuf-l Not tainted 3.16.0-next-20140811 #1
[ 879.567829] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[ 879.568177] 0000000000000000 00000000c532680c ffff880039643d00 ffffffff817aa2d2
[ 879.568776] 0000000000000000 ffff880039643d38 ffffffff8109afbd ffff880039d6ba80
[ 879.569386] ffff88003a449800 000000002983d6bd 0000000000000000 000000002983d6bc
[ 879.569982] Call Trace:
[ 879.570264] [<ffffffff817aa2d2>] dump_stack+0x4d/0x66
[ 879.570599] [<ffffffff8109afbd>] warn_slowpath_common+0x7d/0xa0
[ 879.570935] [<ffffffff8109b0ea>] warn_slowpath_null+0x1a/0x20
[ 879.571292] [<ffffffff816d0a05>] tcp_ack+0x11f5/0x1380
[ 879.571614] [<ffffffff816d10bd>] tcp_rcv_established+0x1ed/0x710
[ 879.571958] [<ffffffff816dc9da>] tcp_v4_do_rcv+0x10a/0x370
[ 879.572315] [<ffffffff81657459>] release_sock+0x89/0x1d0
[ 879.572642] [<ffffffff816c81a0>] do_tcp_setsockopt.isra.36+0x120/0x860
[ 879.573000] [<ffffffff8110a52e>] ? rcu_read_lock_held+0x6e/0x80
[ 879.573352] [<ffffffff816c8912>] tcp_setsockopt+0x32/0x40
[ 879.573678] [<ffffffff81654ac4>] sock_common_setsockopt+0x14/0x20
[ 879.574031] [<ffffffff816537b0>] SyS_setsockopt+0x80/0xf0
[ 879.574393] [<ffffffff817b40a9>] system_call_fastpath+0x16/0x1b
[ 879.574730] ---[ end trace a17cbc38eb8c5c00 ]---
v2: moving setting of skb->when for repaired skb-s in tcp_write_xmit,
where it's set for other skb-s.
Fixes: 431a91242d8d ("tcp: timestamp SYN+DATA messages")
Fixes: 740b0f1841f6 ("tcp: switch rtt estimations to usec resolution")
Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: Pavel Emelyanov <xemul@xxxxxxxxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Signed-off-by: Andrey Vagin <avagin@xxxxxxxxxx>
---
include/net/tcp.h | 4 +++-
net/ipv4/tcp.c | 14 +++++++-------
net/ipv4/tcp_output.c | 5 ++++-
3 files changed, 14 insertions(+), 9 deletions(-)
diff --git a/include/net/tcp.h b/include/net/tcp.h
index dafa1cb..36f5525 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -705,8 +705,10 @@ struct tcp_skb_cb {
#define TCPCB_SACKED_RETRANS 0x02 /* SKB retransmitted */
#define TCPCB_LOST 0x04 /* SKB is lost */
#define TCPCB_TAGBITS 0x07 /* All tag bits */
+#define TCPCB_REPAIRED 0x10 /* SKB repaired (no skb_mstamp) */
#define TCPCB_EVER_RETRANS 0x80 /* Ever retransmitted frame */
-#define TCPCB_RETRANS (TCPCB_SACKED_RETRANS|TCPCB_EVER_RETRANS)
+#define TCPCB_RETRANS (TCPCB_SACKED_RETRANS|TCPCB_EVER_RETRANS| \
+ TCPCB_REPAIRED)
__u8 ip_dsfield; /* IPv4 tos or IPv6 dsfield */
/* 1 byte hole */
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 181b70e..541f26a 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1188,13 +1188,6 @@ new_segment:
goto wait_for_memory;
/*
- * All packets are restored as if they have
- * already been sent.
- */
- if (tp->repair)
- TCP_SKB_CB(skb)->when = tcp_time_stamp;
-
- /*
* Check whether we can use HW checksum.
*/
if (sk->sk_route_caps & NETIF_F_ALL_CSUM)
@@ -1203,6 +1196,13 @@ new_segment:
skb_entail(sk, skb);
copy = size_goal;
max = size_goal;
+
+ /* All packets are restored as if they have
+ * already been sent. skb_mstamp isn't set to
+ * avoid wrong rtt estimation.
+ */
+ if (tp->repair)
+ TCP_SKB_CB(skb)->sacked |= TCPCB_REPAIRED;
}
/* Try to append data to the end of skb. */
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 8fcfc91..a747f01 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1917,8 +1917,11 @@ static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
tso_segs = tcp_init_tso_segs(sk, skb, mss_now);
BUG_ON(!tso_segs);
- if (unlikely(tp->repair) && tp->repair_queue == TCP_SEND_QUEUE)
+ if (unlikely(tp->repair) && tp->repair_queue == TCP_SEND_QUEUE) {
+ /* "when" is used as a start point for the retransmit timer */
+ TCP_SKB_CB(skb)->when = tcp_time_stamp;
goto repair; /* Skip network transmission */
+ }
cwnd_quota = tcp_cwnd_test(tp, skb);
if (!cwnd_quota) {
--
1.9.3
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