Re: [PATCH] tcp: keepalive fixes
From: Yuchung Cheng <hidden>
Date: 2021-01-12 22:49:37
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On Tue, Jan 12, 2021 at 2:31 PM Enke Chen [off-list ref] wrote:
From: Enke Chen <redacted> 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.
quoted hunk ↗ jump to hunk
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 <redacted> --- 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