netdev - Re: [PATCH v5 net-next 01/15] net: bridge: mst: Multiple Spanning Tree (MST) mode

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Date:   Mon, 9 Jan 2023 14:20:02 +0200
From:   Ido Schimmel <idosch@...sch.org>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Tobias Waldekranz <tobias@...dekranz.com>, davem@...emloft.net,
        kuba@...nel.org, Nikolay Aleksandrov <razor@...ckwall.org>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Ivan Vecera <ivecera@...hat.com>,
        Roopa Prabhu <roopa@...dia.com>,
        Russell King <linux@...linux.org.uk>,
        Petr Machata <petrm@...dia.com>,
        Ido Schimmel <idosch@...dia.com>,
        Matt Johnston <matt@...econstruct.com.au>,
        Cooper Lees <me@...perlees.com>, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, bridge@...ts.linux-foundation.org
Subject: Re: [PATCH v5 net-next 01/15] net: bridge: mst: Multiple Spanning
 Tree (MST) mode

On Mon, Jan 09, 2023 at 01:56:53PM +0200, Vladimir Oltean wrote:
> On Mon, Jan 09, 2023 at 01:43:46PM +0200, Ido Schimmel wrote:
> > OK, thanks for confirming. Will send a patch later this week if Tobias
> > won't take care of it by then. First patch will probably be [1] to make
> > sure we dump the correct MST state to user space. It will also make it
> > easier to show the problem and validate the fix.
> > 
> > [1]
> > diff --git a/net/bridge/br.c b/net/bridge/br.c
> > index 4f5098d33a46..f02a1ad589de 100644
> > --- a/net/bridge/br.c
> > +++ b/net/bridge/br.c
> > @@ -286,7 +286,7 @@ int br_boolopt_get(const struct net_bridge *br, enum br_boolopt_id opt)
> >  	case BR_BOOLOPT_MCAST_VLAN_SNOOPING:
> >  		return br_opt_get(br, BROPT_MCAST_VLAN_SNOOPING_ENABLED);
> >  	case BR_BOOLOPT_MST_ENABLE:
> > -		return br_opt_get(br, BROPT_MST_ENABLED);
> > +		return br_mst_is_enabled(br);
> 
> Well, this did report the correct MST state despite the incorrect static
> branch state, no? The users of br_mst_is_enabled(br) are broken, not
> those of br_opt_get(br, BROPT_MST_ENABLED).

I should have said "actual"/"effective" instead of "correct". IMO, it's
better to use the same conditional in the both the data and control
paths to eliminate discrepancies. Without the patch, a user will see
that MST is supposedly enabled when it is actually disabled in the data
path.

> 
> Anyway, I see there's a br_mst_is_enabled() and also a br_mst_enabled()?!
> One is used in the fast path and the other in the slow path. They should
> probably be merged, I guess. They both exist probably because somebody
> thought that the "if (!netif_is_bridge_master(dev))" test is redundant
> in the fast path.

The single user of br_mst_enabled() (DSA) is not affected by the bug
(only the SW data path is), so I suggest making this consolidation in
net-next after the bug is fixed. OK?

> 
> >  	default:
> >  		/* shouldn't be called with unsupported options */
> >  		WARN_ON(1);
> > diff --git a/net/bridge/br_private.h b/net/bridge/br_private.h
> > index 75aff9bbf17e..7f0475f62d45 100644
> > --- a/net/bridge/br_private.h
> > +++ b/net/bridge/br_private.h
> > @@ -1827,7 +1827,7 @@ static inline bool br_vlan_state_allowed(u8 state, bool learn_allow)
> >  /* br_mst.c */
> >  #ifdef CONFIG_BRIDGE_VLAN_FILTERING
> >  DECLARE_STATIC_KEY_FALSE(br_mst_used);
> > -static inline bool br_mst_is_enabled(struct net_bridge *br)
> > +static inline bool br_mst_is_enabled(const struct net_bridge *br)
> >  {
> >  	return static_branch_unlikely(&br_mst_used) &&
> >  		br_opt_get(br, BROPT_MST_ENABLED);
> > @@ -1845,7 +1845,7 @@ int br_mst_fill_info(struct sk_buff *skb,
> >  int br_mst_process(struct net_bridge_port *p, const struct nlattr *mst_attr,
> >  		   struct netlink_ext_ack *extack);
> >  #else
> > -static inline bool br_mst_is_enabled(struct net_bridge *br)
> > +static inline bool br_mst_is_enabled(const struct net_bridge *br)
> >  {
> >  	return false;
> >  }