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From: Jason Gunthorpe <>
To: Christoph Lameter <>
Cc:, Leon Romanovsky <>
Subject: Re: [PATCH][FIX] ROCE Multicast: Do not send IGMP leaves for sendonly Multicast groups
Date: Tue, 14 Sep 2021 15:57:43 -0300	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

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 <>

I added the missing fixes line:

    Fixes: ab15c95a17b3 ("IB/core: Support for CMA multicast join flags")

Applied to for-rc, thanks


      parent reply	other threads:[~2021-09-14 18:57 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-08 11:43 Christoph Lameter
2021-09-13 10:38 ` Leon Romanovsky
2021-09-14 18:38   ` Jason Gunthorpe
2021-09-15 19:44   ` Christoph Lameter
2021-09-14 18:57 ` Jason Gunthorpe [this message]

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