Re: [PATCH net 1/1] net: bridge: cfm: use a per-bridge frame type

On Fri, Aug 28, 2026 at 3:23 AM Nikolay Aleksandrov <[email protected]> wrote:
>
> On 12/05/2026 11:09, Nikolay Aleksandrov wrote:
> > On 12/05/2026 08:21, Yilin Zhu wrote:
> >> On Sun, 10 May 2026 at 04:40, Nikolay Aleksandrov <[email protected]> wrote:
> >>>
> >>> On 10/05/2026 13:05, Nikolay Aleksandrov wrote:
> >>>> On 10/05/2026 12:15, Ren Wei wrote:
> >>>>> From: Yilin Zhu <[email protected]>
> >>>>>
> >>>>> CFM registers a bridge frame handler when the first MEP is created and
> >>>>> unregisters it when the last MEP is deleted. The registered object also
> >>>>> contains the hlist_node used by the bridge-local frame_type_list.
> >>>>>
> >>>>> The CFM frame type is currently global, so enabling CFM on multiple
> >>>>> bridges links the same hlist_node into multiple bridge-local lists. A
> >>>>> later unregister on one bridge can then operate on list state belonging
> >>>>> to another bridge.
> >>>>>
> >>>>> Move the CFM frame type into struct net_bridge and register/unregister
> >>>>> the bridge-owned object. This keeps frame handler list membership local
> >>>>> to the bridge while preserving the existing first-MEP/last-MEP lifetime.
> >>>>>
> >>>>> Fixes: dc32cbb3dbd7 ("bridge: cfm: Kernel space implementation of CFM. CCM
> >>>>> frame RX added.")
> >>>>> Cc: [email protected]
> >>>>> Reported-by: Yuan Tan <[email protected]>
> >>>>> Reported-by: Yifan Wu <[email protected]>
> >>>>> Reported-by: Juefei Pu <[email protected]>
> >>>>> Reported-by: Xin Liu <[email protected]>
> >>>>> Co-developed-by: Peihan Liu <[email protected]>
> >>>>> Signed-off-by: Peihan Liu <[email protected]>
> >>>>> Signed-off-by: Yilin Zhu <[email protected]>
> >>>>> Signed-off-by: Ren Wei <[email protected]>
> >>>>> ---
> >>>>>    net/bridge/br_cfm.c     | 14 ++++++--------
> >>>>>    net/bridge/br_private.h | 18 +++++++++++-------
> >>>>>    2 files changed, 17 insertions(+), 15 deletions(-)
> >>>>>
> >>>>
> >>>> I think MRP suffers from the same bug, but I also think we can contain the
> >>>> fix within the packet type structure instead of making the already huge
> >>>> struct net_bridge even bigger. Also, linking a struct within net_bridge
> >>>> to a list within the same net_bridge looks weird.
> >>>>
> >>>> IMO br_add_frame should take a type & a frame_handler, allocate a br_frame_type
> >>>> dynamically and link it, then br_del_frame should take a type instead of a ptr
> >>>> and remove that frame type and free it with kfree_rcu. That would require
> >>>> br_add_frame return value to be checked in the respective cfm/mrp functions.
> >>>> Warnings for already existing types on add or missing types on del should be
> >>>> added.
> >>>>
> >>>
> >>> Actually I have a better idea since these handlers can be added only once per
> >>> bridge, we can do away with a simple bitmask (e.g. use net_bridge's options
> >>> which is in a Rx hot cache line) and even reduce net_bridge size while fixing
> >>> these bugs, and also remove a conditional from the fast-path when CFM/MRP are
> >>> not compiled in. Would you like me to prepare it or do you want to give it a go?
> >>>
> >>
> >> Hi Nik,
> >>
> >> Thanks for the suggestion.
> >>
> >> I'll give it a go. IIUC, the idea is to remove the shared
> >> br_frame_type list entries for CFM/MRP, track their per-bridge enable
> >> state with bridge option bits, and dispatch the CFM/MRP handlers directly
> >> from the receive path when the corresponding EtherType and option bit
> >> match.
> >>
> >> I'll include MRP in v2.
> >>
> >> Thanks,
> >> Yilin
> >>
> >
> > Great, thank you. That should simplify the code and give us 8 bytes of Rx hot
> > cache line back. The important point is that there haven't been any new
> > handlers since these were added back in 2020, and also these are not
> > common, so making their impact on the fast-path as small as possible
> > while fixing the bug sounds good.
> >
> > A quick & dirty sketch of the fixes gives me:
> > 5 files changed, 47 insertions(+), 66 deletions(-)
> >
> > That can probably be improved (i.e. more deletions).
> >
> > Just please make sure that if CFM/MRP are not enabled in .config, they
> > would not affect the fast-path at all.
> >
> > Cheers,
> >   Nik
> >
>
> Hi Yilin,
> Are you still considering fixing these problems? A few months passed since
> we last spoke.
>
> Cheers,
>   Nik
>
>

Hi Nik,

I’m very sorry for the long delay. Yilin has gone back to continue his
studies and unfortunately no longer has the time to finish this patch.

There was also an issue on my side in keeping track of this work, and
I failed to notice that the patch had been left without a follow-up
for so long. I apologize for that.

I can take over the patch, address the remaining feedback, and send a
new version. That said, I’m not sure whether it might actually be
easier for you to make the changes directly, if you are willing to do
so. I’ve heard from maintainers that reviewing and iterating on
someone else’s patch can sometimes take more effort than simply making
the fix themselves, so I wanted to ask which approach you would
prefer.

If you would prefer to fix the issue directly, could you please
include the following tags?
Reported-by: [email protected]
Reported-by: [email protected]

Otherwise, I’m happy to take over and prepare the next revision.
What would you prefer?

Best,
Yuan