Re: [REGRESSION] Warning in tcp_fastretrans_alert() of net/ipv4/tcp_input.c
From: Oleksandr Natalenko <hidden>
Date: 2017-09-15 05:03:29
Hi. I've applied your test patch but it doesn't fix the issue for me since the warning is still there. Were you able to reproduce it? On pondělí 11. září 2017 1:59:02 CEST Neal Cardwell wrote:
quoted hunk ↗ jump to hunk
Thanks for the detailed report! I suspect this is due to the following commit, which happened between 4.10 and 4.11: 89fe18e44f7e tcp: extend F-RTO to catch more spurious timeouts https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/? id=89fe18e44f7e This commit expanded the set of scenarios where we would undo a CA_Loss cwnd reduction and return to TCP_CA_Open, but did not include a check to see if there were any in-flight retransmissions. I think we need a fix like the following:diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 659d1baefb2b..730a2de9d2b0 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c@@ -2439,7 +2439,7 @@ static bool tcp_try_undo_loss(struct sock *sk,bool frto_undo) { struct tcp_sock *tp = tcp_sk(sk); - if (frto_undo || tcp_may_undo(tp)) { + if ((frto_undo || tcp_may_undo(tp)) && !tp->retrans_out) { tcp_undo_cwnd_reduction(sk, true); DBGUNDO(sk, "partial loss"); I will try a packetdrill test to see if I can reproduce this issue and verify the fix. thanks, neal