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.
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;
> }
> 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
