2022-03-14 19:46:24

by Vladimir Oltean

Subject: Re: [PATCH v3 net-next 03/14] net: bridge: mst: Support setting and reporting MST port states

On Mon, Mar 14, 2022 at 10:52:20AM +0100, Tobias Waldekranz wrote:
> +int br_mst_fill_info(struct sk_buff *skb, struct net_bridge_vlan_group *vg)
> +{
> + struct net_bridge_vlan *v;
> + struct nlattr *nest;
> + unsigned long *seen;
> + int err = 0;
> +
> + seen = bitmap_zalloc(VLAN_N_VID, 0);

I see there is precedent in the bridge driver for using dynamic
allocation as opposed to on-stack declaration using DECLARE_BITMAP().
I imagine this isn't just to be "heapsters", but why?

I don't have a very good sense of how much on-stack memory is too much
(a lot probably depends on the expected depth of the call stack too, and here it
doesn't appear to be too deep), but I see that mlxsw_sp_bridge_vxlan_vlan_is_valid()
has a DECLARE_BITMAP(vlans, VLAN_N_VID) too.

The comment applies for callers of br_mst_get_info() too.

> + if (!seen)
> + return -ENOMEM;
> +
> + list_for_each_entry(v, &vg->vlan_list, vlist) {
> + if (test_bit(v->brvlan->msti, seen))
> + continue;
> +
> + nest = nla_nest_start_noflag(skb, IFLA_BRIDGE_MST_ENTRY);
> + if (!nest ||
> + nla_put_u16(skb, IFLA_BRIDGE_MST_ENTRY_MSTI, v->brvlan->msti) ||
> + nla_put_u8(skb, IFLA_BRIDGE_MST_ENTRY_STATE, v->state)) {
> + err = -EMSGSIZE;
> + break;
> + }
> + nla_nest_end(skb, nest);
> +
> + set_bit(v->brvlan->msti, seen);
> + }
> +
> + kfree(seen);
> + return err;
> +}

2022-03-16 13:18:58

by Tobias Waldekranz

Subject: Re: [PATCH v3 net-next 03/14] net: bridge: mst: Support setting and reporting MST port states

On Mon, Mar 14, 2022 at 16:58, Vladimir Oltean <[email protected]> wrote:
> On Mon, Mar 14, 2022 at 10:52:20AM +0100, Tobias Waldekranz wrote:
>> +int br_mst_fill_info(struct sk_buff *skb, struct net_bridge_vlan_group *vg)
>> +{
>> + struct net_bridge_vlan *v;
>> + struct nlattr *nest;
>> + unsigned long *seen;
>> + int err = 0;
>> +
>> + seen = bitmap_zalloc(VLAN_N_VID, 0);
>
> I see there is precedent in the bridge driver for using dynamic
> allocation as opposed to on-stack declaration using DECLARE_BITMAP().
> I imagine this isn't just to be "heapsters", but why?
>
> I don't have a very good sense of how much on-stack memory is too much
> (a lot probably depends on the expected depth of the call stack too, and here it
> doesn't appear to be too deep), but I see that mlxsw_sp_bridge_vxlan_vlan_is_valid()
> has a DECLARE_BITMAP(vlans, VLAN_N_VID) too.
>
> The comment applies for callers of br_mst_get_info() too.

In v4, things become even worse, as I need to allocate the bitmap in a
context where I can't return an error. So if it's ok to keep it on the
stack, then that would be great.

Here's the code in question:

size_t br_mst_info_size(const struct net_bridge_vlan_group *vg)
{
const struct net_bridge_vlan *v;
unsigned long *seen;
size_t sz;

seen = bitmap_zalloc(VLAN_N_VID, 0);
if (WARN_ON(!seen))
return 0;

/* IFLA_BRIDGE_MST */
sz = nla_total_size(0);

list_for_each_entry(v, &vg->vlan_list, vlist) {
if (test_bit(v->brvlan->msti, seen))
continue;

/* IFLA_BRIDGE_MST_ENTRY */
sz += nla_total_size(0) +
/* IFLA_BRIDGE_MST_ENTRY_MSTI */
nla_total_size(sizeof(u16)) +
/* IFLA_BRIDGE_MST_ENTRY_STATE */
nla_total_size(sizeof(u8));

__set_bit(v->brvlan->msti, seen);
}

kfree(seen);
return sz;
}