[PATCH net-next 0/2] ipv6: fix hangup on device removal

[PATCH net-next 0/2] ipv6: fix hangup on device removal

[Paolo Abeni]

This addresses the infamous unregister_netdevice splat in net selftests;
the actual fix is carried by the first patch, while the 2nd one
addresses a related problem in the relevant test that was patially
hiding the problem.

Targeting net-next as the issue is quite old and I feel a little lost
in the fib info/nh jungle.

Paolo Abeni (2):
  ipv6: release nexthop on device removal
  selftests: net: really check for bg process completion

 net/ipv6/route.c                    | 7 ++++---
 tools/testing/selftests/net/pmtu.sh | 2 +-
 2 files changed, 5 insertions(+), 4 deletions(-)

-- 
2.45.2

[PATCH net-next 1/2] ipv6: release nexthop on device removal

[Paolo Abeni]

The CI is hitting some aperiodic hangup at device removal time in the
pmtu.sh self-test:

unregister_netdevice: waiting for veth_A-R1 to become free. Usage count = 6
ref_tracker: veth_A-R1@ffff888013df15d8 has 1/5 users at
	dst_init+0x84/0x4a0
	dst_alloc+0x97/0x150
	ip6_dst_alloc+0x23/0x90
	ip6_rt_pcpu_alloc+0x1e6/0x520
	ip6_pol_route+0x56f/0x840
	fib6_rule_lookup+0x334/0x630
	ip6_route_output_flags+0x259/0x480
	ip6_dst_lookup_tail.constprop.0+0x5c2/0x940
	ip6_dst_lookup_flow+0x88/0x190
	udp_tunnel6_dst_lookup+0x2a7/0x4c0
	vxlan_xmit_one+0xbde/0x4a50 [vxlan]
	vxlan_xmit+0x9ad/0xf20 [vxlan]
	dev_hard_start_xmit+0x10e/0x360
	__dev_queue_xmit+0xf95/0x18c0
	arp_solicit+0x4a2/0xe00
	neigh_probe+0xaa/0xf0

While the first suspect is the dst_cache, explicitly tracking the dst
owing the last device reference via probes proved such dst is held by
the nexthop in the originating fib6_info.

Similar to commit f5b51fe804ec ("ipv6: route: purge exception on
removal"), we need to explicitly release the originating fib info when
disconnecting a to-be-removed device from a live ipv6 dst: move the
fib6_info cleanup into ip6_dst_ifdown().

Tested running:

./pmtu.sh cleanup_ipv6_exception

in a tight loop for more than 400 iterations with no spat, running an
unpatched kernel  I observed a splat every ~10 iterations.

Fixes: f88d8ea67fbd ("ipv6: Plumb support for nexthop object in a fib6_info")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
 net/ipv6/route.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index d7ce5cf2017a..ef55f330dcda 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -187,6 +187,7 @@ static void rt6_uncached_list_flush_dev(struct net_device *dev)
 						   GFP_ATOMIC);
 				handled = true;
 			}
+
 			if (handled)
 				list_del_init(&rt->dst.rt_uncached);
 		}
@@ -374,6 +375,7 @@ static void ip6_dst_ifdown(struct dst_entry *dst, struct net_device *dev)
 {
 	struct rt6_info *rt = dst_rt6_info(dst);
 	struct inet6_dev *idev = rt->rt6i_idev;
+	struct fib6_info *from;
 
 	if (idev && idev->dev != blackhole_netdev) {
 		struct inet6_dev *blackhole_idev = in6_dev_get(blackhole_netdev);
@@ -383,6 +385,8 @@ static void ip6_dst_ifdown(struct dst_entry *dst, struct net_device *dev)
 			in6_dev_put(idev);
 		}
 	}
+	from = unrcu_pointer(xchg(&rt->from, NULL));
+	fib6_info_release(from);
 }
 
 static bool __rt6_check_expired(const struct rt6_info *rt)
@@ -1455,7 +1459,6 @@ static DEFINE_SPINLOCK(rt6_exception_lock);
 static void rt6_remove_exception(struct rt6_exception_bucket *bucket,
 				 struct rt6_exception *rt6_ex)
 {
-	struct fib6_info *from;
 	struct net *net;
 
 	if (!bucket || !rt6_ex)
@@ -1467,8 +1470,6 @@ static void rt6_remove_exception(struct rt6_exception_bucket *bucket,
 	/* purge completely the exception to allow releasing the held resources:
 	 * some [sk] cache may keep the dst around for unlimited time
 	 */
-	from = unrcu_pointer(xchg(&rt6_ex->rt6i->from, NULL));
-	fib6_info_release(from);
 	dst_dev_put(&rt6_ex->rt6i->dst);
 
 	hlist_del_rcu(&rt6_ex->hlist);
-- 
2.45.2

[PATCH net-next 2/2] selftests: net: really check for bg process completion

[Paolo Abeni]

A recent refactor transformed the check for process completion
in a true statement, due to a typo.

As a result, the relevant test-case is unable to catch the
regression it was supposed to detect.

Restore the correct condition.

Fixes: 691bb4e49c98 ("selftests: net: avoid just another constant wait")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
 tools/testing/selftests/net/pmtu.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/net/pmtu.sh b/tools/testing/selftests/net/pmtu.sh
index 569bce8b6383..6c651c880fe8 100755
--- a/tools/testing/selftests/net/pmtu.sh
+++ b/tools/testing/selftests/net/pmtu.sh
@@ -2056,7 +2056,7 @@ check_running() {
 	pid=${1}
 	cmd=${2}
 
-	[ "$(cat /proc/${pid}/cmdline 2>/dev/null | tr -d '\0')" = "{cmd}" ]
+	[ "$(cat /proc/${pid}/cmdline 2>/dev/null | tr -d '\0')" = "${cmd}" ]
 }
 
 test_cleanup_vxlanX_exception() {
-- 
2.45.2

Re: [PATCH net-next 1/2] ipv6: release nexthop on device removal

[Paolo Abeni]

On 10/31/24 09:53, Paolo Abeni wrote:
> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> index d7ce5cf2017a..ef55f330dcda 100644
> --- a/net/ipv6/route.c
> +++ b/net/ipv6/route.c
> @@ -187,6 +187,7 @@ static void rt6_uncached_list_flush_dev(struct net_device *dev)
>  						   GFP_ATOMIC);
>  				handled = true;
>  			}
> +

Please do not include unrelated whitespace chang... wait! I'm talking to
myself... in any case a v2 is needed.

/P

Re: [PATCH net-next 1/2] ipv6: release nexthop on device removal

[Eric Dumazet]

On Tue, Nov 5, 2024 at 1:19 PM Paolo Abeni <pabeni@redhat.com> wrote:
>
> On 10/31/24 09:53, Paolo Abeni wrote:
> > diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> > index d7ce5cf2017a..ef55f330dcda 100644
> > --- a/net/ipv6/route.c
> > +++ b/net/ipv6/route.c
> > @@ -187,6 +187,7 @@ static void rt6_uncached_list_flush_dev(struct net_device *dev)
> >                                                  GFP_ATOMIC);
> >                               handled = true;
> >                       }
> > +
>
> Please do not include unrelated whitespace chang... wait! I'm talking to
> myself... in any case a v2 is needed.

Oh, I missed this patch, thanks a lot for sorting it out.