This is a note to let you know that I've just added the patch titled
tcp: fix wrong RTO timeout when received SACK reneging
to the 5.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
tcp-fix-wrong-rto-timeout-when-received-sack-renegin.patch
and it can be found in the queue-5.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 702052a5e2809f8fada9f01e173e4a1597fdae9f
Author: Fred Chen <fred.chenchen03@xxxxxxxxx>
Date: Sat Oct 21 08:19:47 2023 +0800
tcp: fix wrong RTO timeout when received SACK reneging
[ Upstream commit d2a0fc372aca561556e765d0a9ec365c7c12f0ad ]
This commit fix wrong RTO timeout when received SACK reneging.
When an ACK arrived pointing to a SACK reneging, tcp_check_sack_reneging()
will rearm the RTO timer for min(1/2*srtt, 10ms) into to the future.
But since the commit 62d9f1a6945b ("tcp: fix TLP timer not set when
CA_STATE changes from DISORDER to OPEN") merged, the tcp_set_xmit_timer()
is moved after tcp_fastretrans_alert()(which do the SACK reneging check),
so the RTO timeout will be overwrited by tcp_set_xmit_timer() with
icsk_rto instead of 1/2*srtt.
Here is a packetdrill script to check this bug:
0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+0 bind(3, ..., ...) = 0
+0 listen(3, 1) = 0
// simulate srtt to 100ms
+0 < S 0:0(0) win 32792 <mss 1000, sackOK,nop,nop,nop,wscale 7>
+0 > S. 0:0(0) ack 1 <mss 1460,nop,nop,sackOK,nop,wscale 7>
+.1 < . 1:1(0) ack 1 win 1024
+0 accept(3, ..., ...) = 4
+0 write(4, ..., 10000) = 10000
+0 > P. 1:10001(10000) ack 1
// inject sack
+.1 < . 1:1(0) ack 1 win 257 <sack 1001:10001,nop,nop>
+0 > . 1:1001(1000) ack 1
// inject sack reneging
+.1 < . 1:1(0) ack 1001 win 257 <sack 9001:10001,nop,nop>
// we expect rto fired in 1/2*srtt (50ms)
+.05 > . 1001:2001(1000) ack 1
This fix remove the FLAG_SET_XMIT_TIMER from ack_flag when
tcp_check_sack_reneging() set RTO timer with 1/2*srtt to avoid
being overwrited later.
Fixes: 62d9f1a6945b ("tcp: fix TLP timer not set when CA_STATE changes from DISORDER to OPEN")
Signed-off-by: Fred Chen <fred.chenchen03@xxxxxxxxx>
Reviewed-by: Neal Cardwell <ncardwell@xxxxxxxxxx>
Tested-by: Neal Cardwell <ncardwell@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index ec3c23adbab44..c3f227c4c3567 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2057,16 +2057,17 @@ void tcp_enter_loss(struct sock *sk)
* restore sanity to the SACK scoreboard. If the apparent reneging
* persists until this RTO then we'll clear the SACK scoreboard.
*/
-static bool tcp_check_sack_reneging(struct sock *sk, int flag)
+static bool tcp_check_sack_reneging(struct sock *sk, int *ack_flag)
{
- if (flag & FLAG_SACK_RENEGING &&
- flag & FLAG_SND_UNA_ADVANCED) {
+ if (*ack_flag & FLAG_SACK_RENEGING &&
+ *ack_flag & FLAG_SND_UNA_ADVANCED) {
struct tcp_sock *tp = tcp_sk(sk);
unsigned long delay = max(usecs_to_jiffies(tp->srtt_us >> 4),
msecs_to_jiffies(10));
inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
delay, TCP_RTO_MAX);
+ *ack_flag &= ~FLAG_SET_XMIT_TIMER;
return true;
}
return false;
@@ -2840,7 +2841,7 @@ static void tcp_fastretrans_alert(struct sock *sk, const u32 prior_snd_una,
tp->prior_ssthresh = 0;
/* B. In all the states check for reneging SACKs. */
- if (tcp_check_sack_reneging(sk, flag))
+ if (tcp_check_sack_reneging(sk, ack_flag))
return;
/* C. Check consistency of the current state. */
