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:

quoted

quoted

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 <redacted>

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