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Subject[PATCH 5.4 08/32] tcp: make TCP_USER_TIMEOUT accurate for zero window probes
Date
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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(+)

--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -619,6 +619,7 @@ static inline void tcp_clear_xmit_timers

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)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3295,6 +3295,7 @@ static void tcp_ack_probe(struct sock *s
} 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);
}
--- 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);
}

--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -40,6 +40,24 @@ static u32 tcp_clamp_rto_to_user_timeout
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.

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