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[46.17.184.124]) by smtp.gmail.com with ESMTPSA id u16-20020a056512129000b00448872b44afsm1419319lfs.29.2022.03.14.08.42.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 14 Mar 2022 08:42:02 -0700 (PDT) From: Tobias Waldekranz To: Vladimir Oltean Cc: davem@davemloft.net, kuba@kernel.org, Andrew Lunn , Vivien Didelot , Florian Fainelli , Jiri Pirko , Ivan Vecera , Roopa Prabhu , Nikolay Aleksandrov , Russell King , Ido Schimmel , Petr Machata , Cooper Lees , Matt Johnston , linux-kernel@vger.kernel.org, netdev@vger.kernel.org, bridge@lists.linux-foundation.org Subject: Re: [PATCH v3 net-next 03/14] net: bridge: mst: Support setting and reporting MST port states In-Reply-To: <20220314145854.shtnvetounjfnu4e@skbuf> References: <20220314095231.3486931-1-tobias@waldekranz.com> <20220314095231.3486931-4-tobias@waldekranz.com> <20220314145854.shtnvetounjfnu4e@skbuf> Date: Mon, 14 Mar 2022 16:42:01 +0100 Message-ID: <87y21clewm.fsf@waldekranz.com> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Mon, Mar 14, 2022 at 16:58, Vladimir Oltean 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; }