From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Tue, 6 Aug 2013 00:40:59 +0200 From: Linus =?utf-8?Q?L=C3=BCssing?= Message-ID: <20130805224059.GG25436@Linus-Debian> References: <20130730.161035.1646022729333223847.davem@davemloft.net> <1375311980-25575-1-git-send-email-linus.luessing@web.de> <20130731.174037.1794753574143053874.davem@davemloft.net> <1375692066.25148.14.camel@x61.thuisdomein> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1375692066.25148.14.camel@x61.thuisdomein> Subject: Re: [Bridge] [PATCHv3] bridge: disable snooping if there is no querier List-Id: Linux Ethernet Bridging List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paul Bolle Cc: herbert@gondor.apana.org.au, netdev@vger.kernel.org, bridge@lists.linux-foundation.org, linux-kernel@vger.kernel.org, linux@baker-net.org.uk, stephen@networkplumber.org, linus.luessing@web.de, David Miller , amwang@redhat.com Thanks for the very quick reporting! Looks like my gcc was and still isn't as supportive... You and the lists should have received a patch to fix that. Cheers, Linus On Mon, Aug 05, 2013 at 10:41:06AM +0200, Paul Bolle wrote: > On Wed, 2013-07-31 at 17:40 -0700, David Miller wrote: > > > If there is no querier on a link then we won't get periodic reports and > > > therefore won't be able to learn about multicast listeners behind ports, > > > potentially leading to lost multicast packets, especially for multicast > > > listeners that joined before the creation of the bridge. > > > > > > These lost multicast packets can appear since c5c23260594 > > > ("bridge: Add multicast_querier toggle and disable queries by default") > > > in particular. > > > > > > With this patch we are flooding multicast packets if our querier is > > > disabled and if we didn't detect any other querier. > > > > > > A grace period of the Maximum Response Delay of the querier is added to > > > give multicast responses enough time to arrive and to be learned from > > > before disabling the flooding behaviour again. > > > > > > Signed-off-by: Linus Lüssing > > > > Looks good, applied, thanks Linus. > > 0) This patch is part of v3.11-rc4 as commit b00589af3b0. It introduced > a GCC warning: > net/bridge/br_multicast.c: In function ‘br_multicast_rcv’: > net/bridge/br_multicast.c:1081:36: warning: ‘max_delay’ may be used uninitialized in this function [-Wmaybe-uninitialized] > net/bridge/br_multicast.c:1178:16: note: ‘max_delay’ was declared here > > 1) Summarized, the code reads: > > unsigned long max_delay; > > if (skb->len == sizeof(*mld)) > max_delay = msecs_to_jiffies(ntohs(mld->mld_maxdelay)); > else if (skb->len >= sizeof(*mld2q)) > max_delay = mld2q->mld2q_mrc ? MLDV2_MRC(ntohs(mld2q->mld2q_mrc)) : 1; > > br_multicast_query_received(br, port, !ipv6_addr_any(&ip6h->saddr), > max_delay); > > So GCC notices that max_delay is still uninitialized if skb->len is > neither equal to sizeof(*mld) nor equal or bigger than sizeof(*mld2q). > To me it looks GCC is right here. At least, it is not obvious that > max_delay will actually not be used in br_multicast_query_received() if > it still is uninitialized. > > 2) I'm entirely unfamiliar to this code. So I can't say how this warning > might be silenced. > > > Paul Bolle >