On Thu, May 18, 2023 at 6:18 AM Paolo Abeni <pabeni@xxxxxxxxxx> wrote:
>
> On Tue, 2023-05-16 at 21:22 -0400, Xin Long wrote:
> > When doing plpmtu probe, the probe size is growing every time when it
> > receives the ACK during the Search state until the probe fails. When
> > the failure occurs, pl.probe_high is set and it goes to the Complete
> > state.
> >
> > However, if the link pmtu is huge, like 65535 in loopback_dev, the probe
> > eventually keeps using SCTP_MAX_PLPMTU as the probe size and never fails.
> > Because of that, pl.probe_high can not be set, and the plpmtu probe can
> > never go to the Complete state.
> >
> > Fix it by setting pl.probe_high to SCTP_MAX_PLPMTU when the probe size
> > grows to SCTP_MAX_PLPMTU in sctp_transport_pl_recv(). Also, increase
> > the probe size only when the next is less than SCTP_MAX_PLPMTU.
> >
> > Fixes: b87641aff9e7 ("sctp: do state transition when a probe succeeds on HB ACK recv path")
> > Signed-off-by: Xin Long <lucien.xin@xxxxxxxxx>
> > ---
> > net/sctp/transport.c | 11 +++++++----
> > 1 file changed, 7 insertions(+), 4 deletions(-)
> >
> > diff --git a/net/sctp/transport.c b/net/sctp/transport.c
> > index 2f66a2006517..b0ccfaa4c1d1 100644
> > --- a/net/sctp/transport.c
> > +++ b/net/sctp/transport.c
> > @@ -324,9 +324,11 @@ bool sctp_transport_pl_recv(struct sctp_transport *t)
> > t->pl.probe_size += SCTP_PL_BIG_STEP;
> > } else if (t->pl.state == SCTP_PL_SEARCH) {
> > if (!t->pl.probe_high) {
> > - t->pl.probe_size = min(t->pl.probe_size + SCTP_PL_BIG_STEP,
> > - SCTP_MAX_PLPMTU);
> > - return false;
> > + if (t->pl.probe_size + SCTP_PL_BIG_STEP < SCTP_MAX_PLPMTU) {
> > + t->pl.probe_size += SCTP_PL_BIG_STEP;
> > + return false;
> > + }
> > + t->pl.probe_high = SCTP_MAX_PLPMTU;
>
> It looks like this way the probed mtu can't reach SCTP_MAX_PLPMTU
> anymore, while it was possible before.
indeed.
>
> What about something alike:
>
> if (!t->pl.probe_high) {
> if (t->pl.probe_size < SCTP_MAX_PLPMTU) {
> t->pl.probe_size = min(t->pl.probe_size + SCTP_PL_BIG_STEP,
> SCTP_MAX_PLPMTU);
> return false;
> }
> t->pl.probe_high = SCTP_MAX_PLPMTU;
looks good.
will post v2.
Thanks.
> > }
> > t->pl.probe_size += SCTP_PL_MIN_STEP;
> > if (t->pl.probe_size >= t->pl.probe_high) {
> > @@ -341,7 +343,8 @@ bool sctp_transport_pl_recv(struct sctp_transport *t)
> > } else if (t->pl.state == SCTP_PL_COMPLETE) {
> > /* Raise probe_size again after 30 * interval in Search Complete */
> > t->pl.state = SCTP_PL_SEARCH; /* Search Complete -> Search */
> > - t->pl.probe_size += SCTP_PL_MIN_STEP;
> > + if (t->pl.probe_size + SCTP_PL_MIN_STEP < SCTP_MAX_PLPMTU)
> > + t->pl.probe_size += SCTP_PL_MIN_STEP;
>
> In a similar way, should the above check be:
>
> if (t->pl.probe_size + SCTP_PL_MIN_STEP <= SCTP_MAX_PLPMTU)
> t->pl.probe_size += SCTP_PL_MIN_STEP;
>
> or simply:
> t->pl.probe_size = min(t->pl.probe_size + SCTP_PL_MIN_STEP, SCTP_MAX_PLPMTU)
> >
> Cheers,
>
> Paolo
>
