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Date: Sun, 20 Jun 2021 07:25:52 -0700 From: Florian Fainelli <f.fainelli@...il.com> To: Vladimir Oltean <olteanv@...il.com>, Jakub Kicinski <kuba@...nel.org>, "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org Cc: Andrew Lunn <andrew@...n.ch>, Vivien Didelot <vivien.didelot@...il.com>, Vladimir Oltean <vladimir.oltean@....com> Subject: Re: [PATCH net-next 5/6] net: dsa: targeted MTU notifiers should only match on one port On 6/18/2021 11:30 AM, Vladimir Oltean wrote: > From: Vladimir Oltean <vladimir.oltean@....com> > > dsa_slave_change_mtu() calls dsa_port_mtu_change() twice: > - it sends a cross-chip notifier with the MTU of the CPU port which is > used to update the DSA links. > - it sends one targeted MTU notifier which is supposed to only match the > user port on which we are changing the MTU. The "propagate_upstream" > variable is used here to bypass the cross-chip notifier system from > switch.c > > But due to a mistake, the second, targeted notifier matches not only on > the user port, but also on the DSA link which is a member of the same > switch, if that exists. > > And because the DSA links of the entire dst were programmed in a > previous round to the largest_mtu via a "propagate_upstream == true" > notification, then the dsa_port_mtu_change(propagate_upstream == false) > call that is immediately upcoming will break the MTU on the one DSA link > which is chip-wise local to the dp whose MTU is changing right now. > > Example given this daisy chain topology: > > sw0p0 sw0p1 sw0p2 sw0p3 sw0p4 > [ cpu ] [ user ] [ user ] [ dsa ] [ user ] > [ x ] [ ] [ ] [ x ] [ ] > | > +---------+ > | > sw1p0 sw1p1 sw1p2 sw1p3 sw1p4 > [ user ] [ user ] [ user ] [ dsa ] [ dsa ] > [ ] [ ] [ ] [ ] [ x ] > > ip link set sw0p1 mtu 9000 > ip link set sw1p1 mtu 9000 # at this stage, sw0p1 and sw1p1 can talk > # to one another using jumbo frames > ip link set sw0p2 mtu 1500 # this programs the sw0p3 DSA link first to > # the largest_mtu of 9000, then reprograms it to > # 1500 with the "propagate_upstream == false" > # notifier, breaking communication between > # sw0p1 and sw1p1 > > To escape from this situation, make the targeted match really match on a > single port - the user port, and rename the "propagate_upstream" > variable to "targeted_match" to clarify the intention and avoid future > issues. > > Signed-off-by: Vladimir Oltean <vladimir.oltean@....com> Reviewed-by: Florian Fainelli <f.fainelli@...il.com> -- Florian
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