Re: [PATCH net-next v1 3/4] net: add granular lock for the netdev netlink socket

[Stanislav Fomichev <stfomichev@gmail.com>]

On 03/09, Mina Almasry wrote:
> On Fri, Mar 7, 2025 at 3:43 PM Stanislav Fomichev <stfomichev@gmail.com> wrote:
> >
> > On 03/07, Jakub Kicinski wrote:
> > > On Fri,  7 Mar 2025 07:57:24 -0800 Stanislav Fomichev wrote:
> > > > diff --git a/net/core/netdev-genl.c b/net/core/netdev-genl.c
> > > > index a219be90c739..8acdeeae24e7 100644
> > > > --- a/net/core/netdev-genl.c
> > > > +++ b/net/core/netdev-genl.c
> > > > @@ -859,6 +859,7 @@ int netdev_nl_bind_rx_doit(struct sk_buff *skb, struct genl_info *info)
> > > >             goto err_genlmsg_free;
> > > >     }
> > > >
> > > > +   mutex_lock(&priv->lock);
> > > >     rtnl_lock();
> > > >
> > > >     netdev = __dev_get_by_index(genl_info_net(info), ifindex);
> > > > @@ -925,6 +926,7 @@ int netdev_nl_bind_rx_doit(struct sk_buff *skb, struct genl_info *info)
> > > >     net_devmem_unbind_dmabuf(binding);
> > > >  err_unlock:
> > > >     rtnl_unlock();
> > > > +   mutex_unlock(&priv->lock);
> > > >  err_genlmsg_free:
> > > >     nlmsg_free(rsp);
> > > >     return err;
> > >
> > > I think you're missing an unlock before successful return here no?
> >
> > Yes, thanks! :-( I have tested some of this code with Mina's latest TX + my
> > loopback mode, but it doesn't have any RX tests.. Will try to hack
> > something together to run RX bind before I repost.
> 
> Is the existing RX test not working for you?
> 
> Also running `./ncdevmem` manually on a driver you have that supports
> devmem will test the binding patch.

It's a bit of a pita to run everything right now since drivers are
not in the tree :-(
 
> I wonder if we can change list_head to xarray, which manages its own
> locking, instead of list_head plus manual locking. Just an idea, I
> don't have a strong preference here. It may be annoying that xarray do
> lookups by an index, so we have to store the index somewhere. But if
> all we do here is add to the xarray and later loop over it to unbind
> elements, we don't need to store the indexes anywhere.

Yeah, having to keep the index around might be a bit awkward. And
since this is not a particularly performance sensitive place, let's
keep it as is for now?