On Wed, Sep 08, 2021 at 01:43:28PM +0200, Christoph Lameter wrote:
> ROCE uses IGMP for Multicast instead of the native Infiniband system where
> joins are required in order to post messages on the Multicast group.
> On Ethernet one can send Multicast messages to arbitrary addresses
> without the need to subscribe to a group.
>
> So ROCE correctly does not send IGMP joins during rdma_join_multicast().
>
> F.e. in cma_iboe_join_multicast() we see:
>
> if (addr->sa_family == AF_INET) {
> if (gid_type == IB_GID_TYPE_ROCE_UDP_ENCAP) {
> ib.rec.hop_limit = IPV6_DEFAULT_HOPLIMIT;
> if (!send_only) {
> err = cma_igmp_send(ndev, &ib.rec.mgid,
> true);
> }
> }
> } else {
>
> So the IGMP join is suppressed as it is unnecessary.
>
> However no such check is done in destroy_mc(). And therefore leaving a
> sendonly multicast group will send an IGMP leave.
>
> This means that the following scenario can lead to a multicast receiver
> unexpectedly being unsubscribed from a MC group:
>
>
> 1. Sender thread does a sendonly join on MC group X. No IGMP join
> is sent.
>
> 2. Receiver thread does a regular join on the same MC Group x.
> IGMP join is sent and the receiver begins to get messages.
>
> 3. Sender thread terminates and destroys MC group X.
> IGMP leave is sent and the receiver no longer receives data.
>
> This patch adds the same logic for sendonly joins to destroy_mc()
> that is also used in cma_iboe_join_multicast().
>
> Signed-off-by: Christoph Lameter <cl@xxxxxxxxx>
I added the missing fixes line:
Fixes: ab15c95a17b3 ("IB/core: Support for CMA multicast join flags")
Applied to for-rc, thanks
Jason
