Re: [PATCH net 2/2] selftests: seg6: add test for dst_cache isolation in seg6 lwtunnel

[Andrea Mayer]

On Tue, 31 Mar 2026 18:15:31 +0200
Nicolas Dichtel <nicolas.dichtel@xxxxxxxxx> wrote:

> Le 31/03/2026 à 13:07, Andrea Mayer a écrit :
> > Add a selftest that verifies the dst_cache in seg6 lwtunnel is not
> > shared between the input (forwarding) and output (locally generated)
> > paths.
> > 
> > The test creates three namespaces (ns_src, ns_router, ns_dst)
> > connected in a line. An SRv6 encap route on ns_router encapsulates
> > traffic destined to cafe::1 with SID fc00::100. The SID is
> > reachable only for forwarded traffic (from ns_src) via an ip rule
> > matching the ingress interface (iif veth-r0 lookup 100), and
> > blackholed in the main table.
> > 
> > The test verifies that:
> > 
> >   1. A packet generated locally on ns_router does not reach
> >      ns_dst with an empty cache, since the SID is blackholed;
> >   2. A forwarded packet from ns_src populates the input cache
> >      from table 100 and reaches ns_dst;
> >   3. A packet generated locally on ns_router still does not
> >      reach ns_dst after the input cache is populated,
> >      confirming the output path does not reuse the input
> >      cache entry.
> > 
> > Both the forwarded and local packets are pinned to the same CPU
> > with taskset, since dst_cache is per-cpu.
> > 
> > Cc: Shuah Khan <shuah@xxxxxxxxxx>
> > Cc: linux-kselftest@xxxxxxxxxxxxxxx
> > Signed-off-by: Andrea Mayer <andrea.mayer@xxxxxxxxxxx>
> > ---
> 
> [snip]
> 
> > +test_cache_isolation()
> > +{
> > +	RET=0
> > +
> > +	# local ping with empty cache: must fail (SID is blackholed)
> > +	if ip netns exec "${NS_RTR}" taskset -c 0 \
> > +			ping6 -c 1 -W 2 "${DEST}" &>/dev/null; then
> > +		echo "SKIP: local ping succeeded with empty cache"
> Nit: maybe the same message as the forwarding case:
> "SKIP: local ping succeeded, topology broken"
> 

Makes sense, will fix in v2.


> > +		exit "${ksft_skip}"
> > +	fi
> > +
> > +	# forward from ns_src to populate the input cache
> > +	if ! ip netns exec "${NS_SRC}" taskset -c 0 \
> > +			ping6 -c 1 -W 2 "${DEST}" &>/dev/null; then
> > +		echo "SKIP: forwarded ping failed, topology broken"
> > +		exit "${ksft_skip}"
> > +	fi
> > +
> [snip]
> 
> After that:
> Reviewed-by: Nicolas Dichtel <nicolas.dichtel@xxxxxxxxx>

Thanks for the review.

Ciao,
Andrea