Re: [PATCH net] tcp: fix TLP timer not set when CA_STATE changes from DISORDER to OPEN

[Pengcheng Yang <yangpc@wangsu.com>]

On Sat, Jan 23, 2021 at 9:27 AM "Jakub Kicinski" <kuba@kernel.org> wrote:
> 
> On Fri, 22 Jan 2021 11:53:46 +0100 Eric Dumazet wrote:
> > On Fri, Jan 22, 2021 at 11:28 AM Pengcheng Yang <yangpc@wangsu.com> wrote:
> > >
> > > When CA_STATE is in DISORDER, the TLP timer is not set when receiving
> > > an ACK (a cumulative ACK covered out-of-order data) causes CA_STATE to
> > > change from DISORDER to OPEN. If the sender is app-limited, it can only
> > > wait for the RTO timer to expire and retransmit.
> > >
> > > The reason for this is that the TLP timer is set before CA_STATE changes
> > > in tcp_ack(), so we delay the time point of calling tcp_set_xmit_timer()
> > > until after tcp_fastretrans_alert() returns and remove the
> > > FLAG_SET_XMIT_TIMER from ack_flag when the RACK reorder timer is set.
> > >
> > > This commit has two additional benefits:
> > > 1) Make sure to reset RTO according to RFC6298 when receiving ACK, to
> > > avoid spurious RTO caused by RTO timer early expires.
> > > 2) Reduce the xmit timer reschedule once per ACK when the RACK reorder
> > > timer is set.
> > >
> > > Link: https://lore.kernel.org/netdev/1611139794-11254-1-git-send-email-yangpc@wangsu.com
> > > Signed-off-by: Pengcheng Yang <yangpc@wangsu.com>
> > > Cc: Neal Cardwell <ncardwell@google.com>
> >
> > This looks like a very nice patch, let me run packetdrill tests on it.
> > 
> > By any chance, have you cooked a packetdrill test showing the issue
> > (failing on unpatched kernel) ?
> 
> Any guidance on backporting / fixes tag? (once the packetdrill
> questions are satisfied)

By reading the commits, we can add:
Fixes: df92c8394e6e ("tcp: fix xmit timer to only be reset if data ACKed/SACKed")