# Re: \[RFC net-next\] net: dsa: rtl8366rb: support bridge offloading

- From: Vladimir Oltean \<olteanv@gmail.com\>
- Date: 2021-03-02 21:21:23 
- List: netdev
- Page: https://ratatoskr.run/netdev/2021/03/6285849
- Thread: https://ratatoskr.run/netdev/2021/02/6277364/t.md

```text
On Tue, Mar 02, 2021 at 05:05:00PM +0100, Linus Walleij wrote:
> On Tue, Mar 2, 2021 at 4:58 AM DENG Qingfang [ref] wrote:
> > On Mon, Mar 1, 2021 at 9:48 PM Linus Walleij [ref] wrote:
> > > With my minor changes:
> > > Tested-by: Linus Walleij <redacted>
> >
> > How about using a mutex lock in port_bridge_{join,leave} ?
> > In my opinion all functions that access multiple registers should be
> > synchronized.
> 
> That's one way, in some cases the framework (DSA) serialize
> the accesses so I don't know if that already happens on a
> higher level? Since it is accessed over a slow bus we should go
> for mutex in that case indeed.

DSA does not serialize this. The .port_bridge_join and
.port_bridge_leave calls are initiated from the NETDEV_CHANGEUPPER net
device event, which is called under rtnl_mutex (see call_netdevice_notifiers).
This is pretty fundamental and I don't think it will ever change.

However, if you still want to add an extra layer of locking (with code
paths that for some reason are not under the rtnl_mutex), then go ahead,
I suppose. It will be challenging to make sure they do something that
isn't snake oil, though.
```