From b2c55af89b513bfc1fb31d8b2864cba29aace6b0 Mon Sep 17 00:00:00 2001 From: Jason Xing Date: Fri, 11 Aug 2023 10:37:47 +0800 Subject: [PATCH] net: fix the RTO timer retransmitting skb every 1ms if linear option is enabled commit e4dd0d3a2f64b8bd8029ec70f52bdbebd0644408 upstream. In the real workload, I encountered an issue which could cause the RTO timer to retransmit the skb per 1ms with linear option enabled. The amount of lost-retransmitted skbs can go up to 1000+ instantly. The root cause is that if the icsk_rto happens to be zero in the 6th round (which is the TCP_THIN_LINEAR_RETRIES value), then it will always be zero due to the changed calculation method in tcp_retransmit_timer() as follows: icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX); Above line could be converted to icsk->icsk_rto = min(0 << 1, TCP_RTO_MAX) = 0 Therefore, the timer expires so quickly without any doubt. I read through the RFC 6298 and found that the RTO value can be rounded up to a certain value, in Linux, say TCP_RTO_MIN as default, which is regarded as the lower bound in this patch as suggested by Eric. Fixes: 36e31b0af587 ("net: TCP thin linear timeouts") Suggested-by: Eric Dumazet Signed-off-by: Jason Xing Reviewed-by: Eric Dumazet Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- net/ipv4/tcp_timer.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c index 0b5d0a2867a8..cf354c29ec12 100644 --- a/net/ipv4/tcp_timer.c +++ b/net/ipv4/tcp_timer.c @@ -586,7 +586,9 @@ out_reset_timer: tcp_stream_is_thin(tp) && icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) { icsk->icsk_backoff = 0; - icsk->icsk_rto = min(__tcp_set_rto(tp), TCP_RTO_MAX); + icsk->icsk_rto = clamp(__tcp_set_rto(tp), + tcp_rto_min(sk), + TCP_RTO_MAX); } else { /* Use normal (exponential) backoff */ icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);