Re: [PATCH v2 net-next 1/8] net: bridge: vlan: notify switchdev only when something changed

[Vladimir Oltean <vladimir.oltean@nxp.com>]

On Tue, Feb 15, 2022 at 01:08:13PM +0200, Nikolay Aleksandrov wrote:
> On 15/02/2022 12:30, Vladimir Oltean wrote:
> > On Tue, Feb 15, 2022 at 12:12:11PM +0200, Nikolay Aleksandrov wrote:
> >> On 15/02/2022 11:54, Vladimir Oltean wrote:
> >>> On Tue, Feb 15, 2022 at 10:54:26AM +0200, Nikolay Aleksandrov wrote:
> >>>>> +/* return true if anything will change as a result of __vlan_add_flags,
> >>>>> + * false otherwise
> >>>>> + */
> >>>>> +static bool __vlan_flags_would_change(struct net_bridge_vlan *v, u16 flags)
> >>>>> +{
> >>>>> +	struct net_bridge_vlan_group *vg;
> >>>>> +	u16 old_flags = v->flags;
> >>>>> +	bool pvid_changed;
> >>>>>  
> >>>>> -	return ret || !!(old_flags ^ v->flags);
> >>>>> +	if (br_vlan_is_master(v))
> >>>>> +		vg = br_vlan_group(v->br);
> >>>>> +	else
> >>>>> +		vg = nbp_vlan_group(v->port);
> >>>>> +
> >>>>> +	if (flags & BRIDGE_VLAN_INFO_PVID)
> >>>>> +		pvid_changed = (vg->pvid == v->vid);
> >>>>> +	else
> >>>>> +		pvid_changed = (vg->pvid != v->vid);
> >>>>> +
> >>>>> +	return pvid_changed || !!(old_flags ^ v->flags);
> >>>>>  }
> >>>>
> >>>> These two have to depend on each other, otherwise it's error-prone and
> >>>> surely in the future someone will forget to update both.
> >>>> How about add a "commit" argument to __vlan_add_flags and possibly rename
> >>>> it to __vlan_update_flags, then add 2 small helpers like __vlan_update_flags_precommit
> >>>> with commit == false and __vlan_update_flags_commit with commit == true.
> >>>> Or some other naming, the point is to always use the same flow and checks
> >>>> when updating the flags to make sure people don't forget.
> >>>
> >>> You want to squash __vlan_flags_would_change() and __vlan_add_flags()
> >>> into a single function? But "would_change" returns bool, and "add"
> >>> returns void.
> >>>
> >>
> >> Hence the wrappers for commit == false and commit == true. You could name the precommit
> >> one __vlan_flags_would_change or something more appropriate. The point is to make
> >> sure we always update both when flags are changed.
> > 
> > I still have a little doubt that I understood you properly.
> > Do you mean like this?
> > 
> 
> By the way I just noticed that __vlan_flags_would_change has another bug, it's testing
> vlan's flags against themselves without any change (old_flags == v->flags).

Yes, I think I noticed that too when I put some debugging prints, I
wasn't sure where it came from though.

> I meant something similar to this (quickly hacked, untested, add flags probably
> could be renamed to something more appropriate):
> 
> diff --git a/net/bridge/br_vlan.c b/net/bridge/br_vlan.c
> index 1402d5ca242d..1de69090d3cb 100644
> --- a/net/bridge/br_vlan.c
> +++ b/net/bridge/br_vlan.c
> @@ -34,53 +34,66 @@ static struct net_bridge_vlan *br_vlan_lookup(struct rhashtable *tbl, u16 vid)
>         return rhashtable_lookup_fast(tbl, &vid, br_vlan_rht_params);
>  }
>  
> -static bool __vlan_add_pvid(struct net_bridge_vlan_group *vg,
> +static void __vlan_add_pvid(struct net_bridge_vlan_group *vg,
>                             const struct net_bridge_vlan *v)
>  {
>         if (vg->pvid == v->vid)
> -               return false;
> +               return;
>  
>         smp_wmb();
>         br_vlan_set_pvid_state(vg, v->state);
>         vg->pvid = v->vid;
> -
> -       return true;
>  }
>  
> -static bool __vlan_delete_pvid(struct net_bridge_vlan_group *vg, u16 vid)
> +static void __vlan_delete_pvid(struct net_bridge_vlan_group *vg, u16 vid)
>  {
>         if (vg->pvid != vid)
> -               return false;
> +               return;
>  
>         smp_wmb();
>         vg->pvid = 0;
> -
> -       return true;
>  }
>  
>  /* return true if anything changed, false otherwise */
> -static bool __vlan_add_flags(struct net_bridge_vlan *v, u16 flags)
> +static bool __vlan_add_flags(struct net_bridge_vlan *v, u16 flags, bool commit)
>  {
>         struct net_bridge_vlan_group *vg;
> -       u16 old_flags = v->flags;
> -       bool ret;
> +       bool change;
>  
>         if (br_vlan_is_master(v))
>                 vg = br_vlan_group(v->br);
>         else
>                 vg = nbp_vlan_group(v->port);
>  
> +       /* check if anything would be changed on commit */
> +       change = (!!(flags & BRIDGE_VLAN_INFO_PVID) == !!(vg->pvid != v->vid) ||
> +                 ((flags ^ v->flags) & BRIDGE_VLAN_INFO_UNTAGGED));
> +
> +       if (!commit)
> +               goto out;
> +
>         if (flags & BRIDGE_VLAN_INFO_PVID)
> -               ret = __vlan_add_pvid(vg, v);
> +               __vlan_add_pvid(vg, v);
>         else
> -               ret = __vlan_delete_pvid(vg, v->vid);
> +               __vlan_delete_pvid(vg, v->vid);
>  
>         if (flags & BRIDGE_VLAN_INFO_UNTAGGED)
>                 v->flags |= BRIDGE_VLAN_INFO_UNTAGGED;
>         else
>                 v->flags &= ~BRIDGE_VLAN_INFO_UNTAGGED;
>  
> -       return ret || !!(old_flags ^ v->flags);
> +out:
> +       return change;
> +}
> +
> +static bool __vlan_flags_would_change(struct net_bridge_vlan *v, u16 flags)
> +{
> +       return __vlan_add_flags(v, flags, false);
> +}
> +
> +static bool __vlan_flags_commit(struct net_bridge_vlan *v, u16 flags)
> +{
> +       return __vlan_add_flags(v, flags, true);
>  }
>  
>  static int __vlan_vid_add(struct net_device *dev, struct net_bridge *br,

Ah, ok, now I understand what you mean. I'll integrate this, retest and
prepare a v3 if there are no other objections. Thanks!