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Subject: Re: [PATCH 1/3] bridge: mrp: Add br_mrp_unique_ifindex function
To:     Horatiu Vultur <horatiu.vultur@microchip.com>
Cc:     jiri@resnulli.us, ivecera@redhat.com, davem@davemloft.net,
        kuba@kernel.org, roopa@cumulusnetworks.com, andrew@lunn.ch,
        UNGLinuxDriver@microchip.com, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, bridge@lists.linux-foundation.org
References: <20200520130923.3196432-1-horatiu.vultur@microchip.com>
 <20200520130923.3196432-2-horatiu.vultur@microchip.com>
 <cecbdbf0-bb49-1e3c-c163-8e7412c6fcec@cumulusnetworks.com>
 <20200521181337.ory6lxyswatqhoej@soft-dev3.localdomain>
From:   Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Message-ID: <39ba5110-2c2a-6fd9-a3e3-000b52a366dc@cumulusnetworks.com>
Date:   Thu, 21 May 2020 19:58:04 +0300
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On 21/05/2020 21:49, Horatiu Vultur wrote:
> 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@microchip.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.
> 

Did you try using rtnl_dereference() instead of rcu_dereference() ?

>>
>>> +     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;
>>>
>>
>