Messages in this thread | | | From | Tobias Waldekranz <> | Subject | Re: [PATCH v3 net-next 03/14] net: bridge: mst: Support setting and reporting MST port states | Date | Mon, 14 Mar 2022 16:42:01 +0100 |
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On Mon, Mar 14, 2022 at 16:58, Vladimir Oltean <olteanv@gmail.com> 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; }
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