netdev - Re: [PATCH 1/3] bridge: mrp: Add br_mrp_unique

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Message-ID: <20200521181337.ory6lxyswatqhoej@soft-dev3.localdomain>
Date:   Thu, 21 May 2020 18:49:18 +0000
From:   Horatiu Vultur <horatiu.vultur@...rochip.com>
To:     Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
CC:     <jiri@...nulli.us>, <ivecera@...hat.com>, <davem@...emloft.net>,
        <kuba@...nel.org>, <roopa@...ulusnetworks.com>, <andrew@...n.ch>,
        <UNGLinuxDriver@...rochip.com>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <bridge@...ts.linux-foundation.org>
Subject: Re: [PATCH 1/3] bridge: mrp: Add br_mrp_unique_ifindex function

The 05/21/2020 11:16, Nikolay Aleksandrov wrote:
> On 20/05/2020 16:09, Horatiu Vultur wrote:
> > It is not allow to have the same net bridge port part of multiple MRP
> > rings. Therefore add a check if the port is used already in a different
> > MRP. In that case return failure.
> >
> > Fixes: 9a9f26e8f7ea ("bridge: mrp: Connect MRP API with the switchdev API")
> > Signed-off-by: Horatiu Vultur <horatiu.vultur@...rochip.com>
> > ---
> >  net/bridge/br_mrp.c | 31 +++++++++++++++++++++++++++++++
> >  1 file changed, 31 insertions(+)
> >
> > diff --git a/net/bridge/br_mrp.c b/net/bridge/br_mrp.c
> > index d7bc09de4c139..a5a3fa59c078a 100644
> > --- a/net/bridge/br_mrp.c
> > +++ b/net/bridge/br_mrp.c
> > @@ -37,6 +37,32 @@ static struct br_mrp *br_mrp_find_id(struct net_bridge *br, u32 ring_id)
> >       return res;
> >  }
> >
> > +static bool br_mrp_unique_ifindex(struct net_bridge *br, u32 ifindex)
> > +{
> > +     struct br_mrp *mrp;
> > +     bool res = true;
> > +
> > +     rcu_read_lock();
> 
> Why do you need the rcu_read_lock() here when lockdep_rtnl_is_held() is used?
> You should be able to just do rtnl_dereference() below as this is used only
> under rtnl.

Hi Nik,

Also initially I thought that is not needed, but when I enabled all the
RCU debug configs to see if I use correctly the RCU, I got a warning
regarding suspicious RCU usage.
And that is the reason why I have put it.

> 
> > +     list_for_each_entry_rcu(mrp, &br->mrp_list, list,
> > +                             lockdep_rtnl_is_held()) {
> > +             struct net_bridge_port *p;
> > +
> > +             p = rcu_dereference(mrp->p_port);
> > +             if (p && p->dev->ifindex == ifindex) {
> > +                     res = false;
> > +                     break;
> > +             }
> > +
> > +             p = rcu_dereference(mrp->s_port);
> > +             if (p && p->dev->ifindex == ifindex) {
> > +                     res = false;
> > +                     break;
> > +             }
> > +     }
> > +     rcu_read_unlock();
> > +     return res;
> > +}
> > +
> >  static struct br_mrp *br_mrp_find_port(struct net_bridge *br,
> >                                      struct net_bridge_port *p)
> >  {
> > @@ -255,6 +281,11 @@ int br_mrp_add(struct net_bridge *br, struct br_mrp_instance *instance)
> >           !br_mrp_get_port(br, instance->s_ifindex))
> >               return -EINVAL;
> >
> > +     /* It is not possible to have the same port part of multiple rings */
> > +     if (!br_mrp_unique_ifindex(br, instance->p_ifindex) ||
> > +         !br_mrp_unique_ifindex(br, instance->s_ifindex))
> > +             return -EINVAL;
> > +
> >       mrp = kzalloc(sizeof(*mrp), GFP_KERNEL);
> >       if (!mrp)
> >               return -ENOMEM;
> >
> 

-- 
/Horatiu