4.19-stable review patch. If anyone has any objections, please let me know.
------------------
From: Jason Xing <kernelxing@xxxxxxxxxxx>
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 <edumazet@xxxxxxxxxx>
Signed-off-by: Jason Xing <kernelxing@xxxxxxxxxxx>
Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
net/ipv4/tcp_timer.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -549,7 +549,9 @@ 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);
