netdev - Re: [PATCH net v2] ipv6: route: purge exception on removal

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Date:   Thu, 21 Feb 2019 10:10:32 -0500
From:   David Ahern <dsahern@...il.com>
To:     Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH net v2] ipv6: route: purge exception on removal

On 2/20/19 12:18 PM, Paolo Abeni wrote:
> When a netdevice is unregistered, we flush the relevant exception
> via rt6_sync_down_dev() -> fib6_ifdown() -> fib6_del() -> fib6_del_route().
> 
> Finally, we end-up calling rt6_remove_exception(), where we release
> the relevant dst, while we keep the references to the related fib6_info and
> dev. Such references should be released later when the dst will be
> destroyed.
> 
> There are a number of caches that can keep the exception around for an
> unlimited amount of time - namely dst_cache, possibly even socket cache.
> As a result device registration may hang, as demonstrated by this script:
> 
> ip netns add cl
> ip netns add rt
> ip netns add srv
> ip netns exec rt sysctl -w net.ipv6.conf.all.forwarding=1
> 
> ip link add name cl_veth type veth peer name cl_rt_veth
> ip link set dev cl_veth netns cl
> ip -n cl link set dev cl_veth up
> ip -n cl addr add dev cl_veth 2001::2/64
> ip -n cl route add default via 2001::1
> 
> ip -n cl link add tunv6 type ip6tnl mode ip6ip6 local 2001::2 remote 2002::1 hoplimit 64 dev cl_veth
> ip -n cl link set tunv6 up
> ip -n cl addr add 2013::2/64 dev tunv6
> 
> ip link set dev cl_rt_veth netns rt
> ip -n rt link set dev cl_rt_veth up
> ip -n rt addr add dev cl_rt_veth 2001::1/64
> 
> ip link add name rt_srv_veth type veth peer name srv_veth
> ip link set dev srv_veth netns srv
> ip -n srv link set dev srv_veth up
> ip -n srv addr add dev srv_veth 2002::1/64
> ip -n srv route add default via 2002::2
> 
> ip -n srv link add tunv6 type ip6tnl mode ip6ip6 local 2002::1 remote 2001::2 hoplimit 64 dev srv_veth
> ip -n srv link set tunv6 up
> ip -n srv addr add 2013::1/64 dev tunv6
> 
> ip link set dev rt_srv_veth netns rt
> ip -n rt link set dev rt_srv_veth up
> ip -n rt addr add dev rt_srv_veth 2002::2/64
> 
> ip netns exec srv netserver & sleep 0.1
> ip netns exec cl ping6 -c 4 2013::1
> ip netns exec cl netperf -H 2013::1 -t TCP_STREAM -l 3 & sleep 1
> ip -n rt link set dev rt_srv_veth mtu 1400
> wait %2
> 
> ip -n cl link del cl_veth
> 
> This commit addresses the issue purging all the references held by the
> exception at time, as we currently do for e.g. ipv6 pcpu dst entries.
> 
> v1 -> v2:
>  - re-order the code to avoid accessing dst and net after dst_dev_put()
> 
> Fixes: 93531c674315 ("net/ipv6: separate handling of FIB entries from dst based routes")
> Signed-off-by: Paolo Abeni <pabeni@...hat.com>
> ---
>  net/ipv6/route.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 

I am surprised this was not found by the existing pmtu script which
creates exceptions. Please add this test case to selftests to capture
this specific set of events.

Reviewed-by: David Ahern <dsahern@...il.com>

Thanks for the resolving.