On Wed, Mar 7, 2018 at 7:59 AM, Ilpo Järvinen <ilpo.jarvi...@helsinki.fi> wrote: > A bogus undo may/will trigger when the loss recovery state is > kept until snd_una is above high_seq. If tcp_any_retrans_done > is zero, retrans_stamp is cleared in this transient state. On > the next ACK, tcp_try_undo_recovery again executes and > tcp_may_undo will always return true because tcp_packet_delayed > has this condition: > return !tp->retrans_stamp || ... > > Check for the false fast retransmit transient condition in > tcp_packet_delayed to avoid bogus undos. Since snd_una may have > advanced on this ACK but CA state still remains unchanged, > prior_snd_una needs to be passed instead of tp->snd_una.
This one also seems like a case where it would be nice to have a specific packet-by-packet example, or trace, or packetdrill scenario. Something that we might be able to translate into a test, or at least to document the issue more explicitly. Thanks! neal