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SubjectRe: [PATCH] tcp: keepalive fixes
On Tue, Jan 12, 2021 at 2:31 PM Enke Chen <enkechen2020@gmail.com> wrote:
>
> From: Enke Chen <enchen@paloaltonetworks.com>
>
> In this patch two issues with TCP keepalives are fixed:
>
> 1) TCP keepalive does not timeout when there are data waiting to be
> delivered and then the connection got broken. The TCP keepalive
> timeout is not evaluated in that condition.
hi enke
Do you have an example to demonstrate this issue -- in theory when
there is data inflight, an RTO timer should be pending (which
considers user-timeout setting). based on the user-timeout description
(man tcp), the user timeout should abort the socket per the specified
time after data commences. some data would help to understand the
issue.

>
> The fix is to remove the code that prevents TCP keepalive from
> being evaluated for timeout.
>
> 2) With the fix for #1, TCP keepalive can erroneously timeout after
> the 0-window probe kicks in. The 0-window probe counter is wrongly
> applied to TCP keepalives.
>
> The fix is to use the elapsed time instead of the 0-window probe
> counter in evaluating TCP keepalive timeout.
>
> Cc: stable@vger.kernel.org
> Signed-off-by: Enke Chen <enchen@paloaltonetworks.com>
> ---
> net/ipv4/tcp_timer.c | 15 +++------------
> 1 file changed, 3 insertions(+), 12 deletions(-)
>
> diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
> index 6c62b9ea1320..40953aa40d53 100644
> --- a/net/ipv4/tcp_timer.c
> +++ b/net/ipv4/tcp_timer.c
> @@ -696,12 +696,6 @@ static void tcp_keepalive_timer (struct timer_list *t)
> ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_SYN_SENT)))
> goto out;
>
> - elapsed = keepalive_time_when(tp);
> -
> - /* It is alive without keepalive 8) */
> - if (tp->packets_out || !tcp_write_queue_empty(sk))
> - goto resched;
> -
> elapsed = keepalive_time_elapsed(tp);
>
> if (elapsed >= keepalive_time_when(tp)) {
> @@ -709,16 +703,15 @@ static void tcp_keepalive_timer (struct timer_list *t)
> * to determine when to timeout instead.
> */
> if ((icsk->icsk_user_timeout != 0 &&
> - elapsed >= msecs_to_jiffies(icsk->icsk_user_timeout) &&
> - icsk->icsk_probes_out > 0) ||
> + elapsed >= msecs_to_jiffies(icsk->icsk_user_timeout)) ||
> (icsk->icsk_user_timeout == 0 &&
> - icsk->icsk_probes_out >= keepalive_probes(tp))) {
> + (elapsed >= keepalive_time_when(tp) +
> + keepalive_intvl_when(tp) * keepalive_probes(tp)))) {
> tcp_send_active_reset(sk, GFP_ATOMIC);
> tcp_write_err(sk);
> goto out;
> }
> if (tcp_write_wakeup(sk, LINUX_MIB_TCPKEEPALIVE) <= 0) {
> - icsk->icsk_probes_out++;
> elapsed = keepalive_intvl_when(tp);
> } else {
> /* If keepalive was lost due to local congestion,
> @@ -732,8 +725,6 @@ static void tcp_keepalive_timer (struct timer_list *t)
> }
>
> sk_mem_reclaim(sk);
> -
> -resched:
> inet_csk_reset_keepalive_timer (sk, elapsed);
> goto out;
>
> --
> 2.29.2
>

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