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Message-ID: <CADvbK_e-J5YKjX6SAx_LZhshqzgi8vZQ0cv-YgS6FvaF5MJPDA@mail.gmail.com> Date: Thu, 18 May 2023 12:53:03 -0400 From: Xin Long <lucien.xin@...il.com> To: Paolo Abeni <pabeni@...hat.com> Cc: network dev <netdev@...r.kernel.org>, linux-sctp@...r.kernel.org, davem@...emloft.net, kuba@...nel.org, Eric Dumazet <edumazet@...gle.com>, Marcelo Ricardo Leitner <marcelo.leitner@...il.com> Subject: Re: [PATCH net] sctp: fix an issue that plpmtu can never go to complete state On Thu, May 18, 2023 at 6:18 AM Paolo Abeni <pabeni@...hat.com> 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@...il.com> > > --- > > 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 >
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