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.