linux-kernel - Re: [PATCH bpf-next v3 4/6] selftests/bpf: refactor xdp_context

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Message-ID: <67be0aa61e400_25ccfc29426@willemb.c.googlers.com.notmuch>
Date: Tue, 25 Feb 2025 13:23:34 -0500
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Marcus Wichelmann <marcus.wichelmann@...zner-cloud.de>, 
 netdev@...r.kernel.org, 
 linux-kernel@...r.kernel.org, 
 bpf@...r.kernel.org, 
 linux-kselftest@...r.kernel.org
Cc: willemdebruijn.kernel@...il.com, 
 jasowang@...hat.com, 
 andrew+netdev@...n.ch, 
 davem@...emloft.net, 
 edumazet@...gle.com, 
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 mykolal@...com, 
 ast@...nel.org, 
 daniel@...earbox.net, 
 martin.lau@...ux.dev, 
 song@...nel.org, 
 yonghong.song@...ux.dev, 
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Subject: Re: [PATCH bpf-next v3 4/6] selftests/bpf: refactor
 xdp_context_functional test and bpf program

Marcus Wichelmann wrote:
> Am 24.02.25 um 16:29 schrieb Marcus Wichelmann:
> > [...]
> > +	/* By default, Linux sends IPv6 multicast listener reports which
> > +	 * interfere with this test. Set the IFF_NOARP flag to ensure
> > +	 * silence on the interface.
> > +	 */
> > +	SYS(close, "ip link set dev " RX_NAME " arp off");
> >   	SYS(close, "ip link set dev " RX_NAME " up");
> 
> Hm, setting the NOARP flag seems to have not been sufficient to fix the flaky
> test:
> https://github.com/kernel-patches/bpf/actions/runs/13507111620/job/37739614229
> 
> I was not able to reproduce it locally or with my own CI runs unfortunately, but
> I'll try something else in the next patch version which should definitely stop
> IPv6 multicast listener report packets from messing with the tests.

You probably want to pass nodad to any ip -6 addr add.

This is a common option you'll find in tools/testing/selftests/net.

RFC 3810 section 5.2.13 says

"
   For stateless autoconfiguration, as defined in [RFC2462], a node is
   required to join several IPv6 multicast groups, in order to perform
   Duplicate Address Detection (DAD).
"