On Mon, Mar 14, 2022 at 16:58, Vladimir Oltean <olteanv@xxxxxxxxx> 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;
}
