netdev - Re: [PATCH net-next 1/4] bridge: Allow enslaving DSA master network devices

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Date:   Thu, 30 Apr 2020 20:50:31 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vivien Didelot <vivien.didelot@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jiri Pirko <jiri@...nulli.us>,
        Ido Schimmel <idosch@...sch.org>,
        Jakub Kicinski <kuba@...nel.org>,
        netdev <netdev@...r.kernel.org>, Li Yang <leoyang.li@....com>,
        Roopa Prabhu <roopa@...ulusnetworks.com>
Subject: Re: [PATCH net-next 1/4] bridge: Allow enslaving DSA master network devices

Hi Nikolay, Roopa,

On Wed, 29 Apr 2020 at 19:33, Nikolay Aleksandrov
<nikolay@...ulusnetworks.com> wrote:
>
> +CC Roopa
>
> On 29/04/2020 19:27, Nikolay Aleksandrov wrote:
> > On 29/04/2020 19:19, Vladimir Oltean wrote:
> >> From: Florian Fainelli <f.fainelli@...il.com>
> >>
> >> Commit 8db0a2ee2c63 ("net: bridge: reject DSA-enabled master netdevices
> >> as bridge members") added a special check in br_if.c in order to check
> >> for a DSA master network device with a tagging protocol configured. This
> >> was done because back then, such devices, once enslaved in a bridge
> >> would become inoperative and would not pass DSA tagged traffic anymore
> >> due to br_handle_frame returning RX_HANDLER_CONSUMED.
> >>
> >> But right now we have valid use cases which do require bridging of DSA
> >> masters. One such example is when the DSA master ports are DSA switch
> >> ports themselves (in a disjoint tree setup). This should be completely
> >> equivalent, functionally speaking, from having multiple DSA switches
> >> hanging off of the ports of a switchdev driver. So we should allow the
> >> enslaving of DSA tagged master network devices.
> >>
> >> Make br_handle_frame() return RX_HANDLER_PASS in order to call into the
> >> DSA specific tagging protocol handlers, and lift the restriction from
> >> br_add_if.
> >>
> >> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
> >> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
> >> ---
> >>  net/bridge/br_if.c    | 4 +---
> >>  net/bridge/br_input.c | 4 +++-
> >>  2 files changed, 4 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/net/bridge/br_if.c b/net/bridge/br_if.c
> >> index ca685c0cdf95..e0fbdb855664 100644
> >> --- a/net/bridge/br_if.c
> >> +++ b/net/bridge/br_if.c
> >> @@ -18,7 +18,6 @@
> >>  #include <linux/rtnetlink.h>
> >>  #include <linux/if_ether.h>
> >>  #include <linux/slab.h>
> >> -#include <net/dsa.h>
> >>  #include <net/sock.h>
> >>  #include <linux/if_vlan.h>
> >>  #include <net/switchdev.h>
> >> @@ -571,8 +570,7 @@ int br_add_if(struct net_bridge *br, struct net_device *dev,
> >>       */
> >>      if ((dev->flags & IFF_LOOPBACK) ||
> >>          dev->type != ARPHRD_ETHER || dev->addr_len != ETH_ALEN ||
> >> -        !is_valid_ether_addr(dev->dev_addr) ||
> >> -        netdev_uses_dsa(dev))
> >> +        !is_valid_ether_addr(dev->dev_addr))
> >>              return -EINVAL;
> >>
> >>      /* No bridging of bridges */
> >> diff --git a/net/bridge/br_input.c b/net/bridge/br_input.c
> >> index d5c34f36f0f4..396bc0c18cb5 100644
> >> --- a/net/bridge/br_input.c
> >> +++ b/net/bridge/br_input.c
> >> @@ -17,6 +17,7 @@
> >>  #endif
> >>  #include <linux/neighbour.h>
> >>  #include <net/arp.h>
> >> +#include <net/dsa.h>
> >>  #include <linux/export.h>
> >>  #include <linux/rculist.h>
> >>  #include "br_private.h"
> >> @@ -263,7 +264,8 @@ rx_handler_result_t br_handle_frame(struct sk_buff **pskb)
> >>      struct sk_buff *skb = *pskb;
> >>      const unsigned char *dest = eth_hdr(skb)->h_dest;
> >>
> >> -    if (unlikely(skb->pkt_type == PACKET_LOOPBACK))
> >> +    if (unlikely(skb->pkt_type == PACKET_LOOPBACK) ||
> >> +        netdev_uses_dsa(skb->dev))
> >>              return RX_HANDLER_PASS;
> >>
> >>      if (!is_valid_ether_addr(eth_hdr(skb)->h_source))
> >>
> >
> > Yet another test in fast-path for all packets.
> > Since br_handle_frame will not be executed at all for such devices I'd suggest
> > to look into a scheme that avoid installing rx_handler and thus prevents br_handle_frame
> > to be called in the frist place. In case that is not possible then we can discuss adding
> > one more test in fast-path.
> >
> > Actually you can just add a dummy rx_handler that simply returns RX_HANDLER_PASS for
> > these devices and keep rx_handler_data so all br_port_get_* will continue working.
> >
> > Thanks,
> >  Nik
> >

Actually both of those are problematic, since br_port_get_check_rcu
and br_port_get_check_rtnl check for the rx_handler pointer against
br_handle_frame.
Actually a plain old revert of 8db0a2ee2c63 works just fine for what I
need it to, not sure if there's any point in making this any more
complicated than that.
What do you think?

Thanks,
-Vladimir