Re: FAILED: patch "[PATCH] tcp: make TCP_USER_TIMEOUT accurate for zero window probes" failed to apply to 5.4-stable tree

[Enke Chen <enkechen2020@gmail.com>]

Hi, Greg:

Attach is the ported patch for the 5.4-stable tree.

Thanks.   -- Enke

> From: <gregkh@linuxfoundation.org>
> Date: Tue, Feb 2, 2021 at 5:15 AM
> Subject: FAILED: patch "[PATCH] tcp: make TCP_USER_TIMEOUT accurate for
> zero window probes" failed to apply to 5.4-stable tree
> To: <enchen@paloaltonetworks.com>, <edumazet@google.com>, <kuba@kernel.org>,
> <ncardwell@google.com>
> Cc: <stable@vger.kernel.org>
> 
> 
> 
> The patch below does not apply to the 5.4-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@vger.kernel.org>.
> 
> thanks,
> 
> greg k-h
> 

tcp: make TCP_USER_TIMEOUT accurate for zero window probes

From: Enke Chen <enchen@paloaltonetworks.com>

commit 344db93ae3ee69fc137bd6ed89a8ff1bf5b0db08 upstream.

The TCP_USER_TIMEOUT is checked by the 0-window probe timer. As the
timer has backoff with a max interval of about two minutes, the
actual timeout for TCP_USER_TIMEOUT can be off by up to two minutes.

In this patch the TCP_USER_TIMEOUT is made more accurate by taking it
into account when computing the timer value for the 0-window probes.

This patch is similar to and builds on top of the one that made
TCP_USER_TIMEOUT accurate for RTOs in commit b701a99e431d ("tcp: Add
tcp_clamp_rto_to_user_timeout() helper to improve accuracy").

Fixes: 9721e709fa68 ("tcp: simplify window probe aborting on USER_TIMEOUT")
Signed-off-by: Enke Chen <enchen@paloaltonetworks.com>
Reviewed-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20210122191306.GA99540@localhost.localdomain
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
 include/net/tcp.h     |  1 +
 net/ipv4/tcp_input.c  |  1 +
 net/ipv4/tcp_output.c |  2 ++
 net/ipv4/tcp_timer.c  | 18 ++++++++++++++++++
 4 files changed, 22 insertions(+)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 377179283c46..424d4f137707 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -619,6 +619,7 @@ static inline void tcp_clear_xmit_timers(struct sock *sk)
 
 unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu);
 unsigned int tcp_current_mss(struct sock *sk);
+u32 tcp_clamp_probe0_to_user_timeout(const struct sock *sk, u32 when);
 
 /* Bound MSS / TSO packet size with the half of the window */
 static inline int tcp_bound_to_half_wnd(struct tcp_sock *tp, int pktsize)
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 7411a4313462..30c1b88ae4f7 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3294,6 +3294,7 @@ static void tcp_ack_probe(struct sock *sk)
 	} else {
 		unsigned long when = tcp_probe0_when(sk, TCP_RTO_MAX);
 
+		when = tcp_clamp_probe0_to_user_timeout(sk, when);
 		tcp_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
 				     when, TCP_RTO_MAX, NULL);
 	}
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 5da6ffce390c..d0774b4e934d 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -3850,6 +3850,8 @@ void tcp_send_probe0(struct sock *sk)
 		 */
 		timeout = TCP_RESOURCE_PROBE_INTERVAL;
 	}
+
+	timeout = tcp_clamp_probe0_to_user_timeout(sk, timeout);
 	tcp_reset_xmit_timer(sk, ICSK_TIME_PROBE0, timeout, TCP_RTO_MAX, NULL);
 }
 
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index 7fcd116fbd37..fa2ae96ecdc4 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -40,6 +40,24 @@ static u32 tcp_clamp_rto_to_user_timeout(const struct sock *sk)
 	return min_t(u32, icsk->icsk_rto, msecs_to_jiffies(remaining));
 }
 
+u32 tcp_clamp_probe0_to_user_timeout(const struct sock *sk, u32 when)
+{
+	struct inet_connection_sock *icsk = inet_csk(sk);
+	u32 remaining;
+	s32 elapsed;
+
+	if (!icsk->icsk_user_timeout || !icsk->icsk_probes_tstamp)
+		return when;
+
+	elapsed = tcp_jiffies32 - icsk->icsk_probes_tstamp;
+	if (unlikely(elapsed < 0))
+		elapsed = 0;
+	remaining = msecs_to_jiffies(icsk->icsk_user_timeout) - elapsed;
+	remaining = max_t(u32, remaining, TCP_TIMEOUT_MIN);
+
+	return min_t(u32, remaining, when);
+}
+
 /**
  *  tcp_write_err() - close socket and save error info
  *  @sk:  The socket the error has appeared on.
-- 
2.29.2