Re: [PATCH net] ipv6/mcast: update mc_qrv when join new group

[Hangbin Liu <liuhangbin@gmail.com>]

On Thu, Nov 08, 2018 at 03:44:10PM +0800, Hangbin Liu wrote:
> On Fri, Oct 26, 2018 at 10:30:54AM +0800, Hangbin Liu wrote:
> > Currently we only set mc_qrv to sysctl_mld_qrv when interface up. If we
> > change sysctl_mld_qrv after interface up, it will has no effect.
> > 
> > Fix it by assigning latest sysctl_mld_qrv to idev mc_qrv when join new group.
> > 
> > Reported-by: Ying Xu <yinxu@redhat.com>
> > Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
> 
> Hi David,
> 
> Any comments for this patch?
> > ---
> >  net/ipv6/mcast.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/net/ipv6/mcast.c b/net/ipv6/mcast.c
> > index dbab62e..bed4890 100644
> > --- a/net/ipv6/mcast.c
> > +++ b/net/ipv6/mcast.c
> > @@ -680,6 +680,7 @@ static void igmp6_group_added(struct ifmcaddr6 *mc)
> >  	if (!(dev->flags & IFF_UP) || (mc->mca_flags & MAF_NOREPORT))
> >  		return;
> >  
> > +	mc->idev->mc_qrv = sysctl_mld_qrv;
> >  	if (mld_in_v1_mode(mc->idev)) {
> >  		igmp6_join_group(mc);
> >  		return;

Hi David,

Sorry for the late reply. Today I find your reply in
https://patchwork.ozlabs.org/patch/989422/, but I could not find your reply
in my local mailbox, even on gmail web side. I can receive other kernel
mails correctly, which is weird...I will check it later.

For your question:

> Why isn't mld_update_qrv() taking care of this?

mld_update_qrv() is used for processing recieved mldv2 query message. This
patch is to init new sysctl_mld_qrv for new joined groups, which haven't
received any mld query message. e.g.

- ipv6_mc_up() - ipv6_mc_reset() set idev->mc_qrv to default sysctl_mld_qrv, which is 2
  - Join group A with qrv = 2
  - user set sysctl_mld_qrv to 3
  - Join group B with qrv = 2  <- Here the new group should set qrv to 3 as
                                  user updated sysctl_mld_qrv. This is the
				  issue this patch want to fix
  - Recived MLDv2 query message
  - Group A, B update new qrv via mld_update_qrv()


> At a minimum, you must make your change take MLD_QRV_DEFAULT etc.
> into account like mld_update_qrv() does.

We should not init mc_qrv to min(MLD_QRV_DEFAULT, sysctl_mld_qrv), or
user will never be able to set mc_qrv greater than 2.

Thanks
Hangbin