[PATCH v1 net-next 0/4] neighbour: Misc follow-ups on per-netns neigh_table series.

[PATCH v1 net-next 0/4] neighbour: Misc follow-ups on per-netns neigh_table series.

[Kuniyuki Iwashima]

Patch 1 updates the switchdev doc, s/arp_tbl/arp_table(net)/.

Patch 2 updates a selftest for per-netns sysctl knobs, though this
is not an actual issue since the test does not hit gc_thresh by
default.

Patches 3 & 4 are based on a suggestion by Ido Schimmel to make
neigh_managed_work CPU-friendly:

  https://lore.kernel.org/netdev/20260902143023.GA3966681@shredder/

Given it's rc7, I'll defer RTNL removal to the next cycle.


Kuniyuki Iwashima (4):
  Documentation: networking: switchdev: Replace arp_tbl with
    arp_table(net).
  selftests: netfilter: Set gc_thresh[123] for gw netns in
    nft_nat_zones.sh.
  neighbour: Schedule neigh_managed_work only when needed.
  neighbour: Floor INTERVAL_PROBE_TIME_MS at 1000.

 Documentation/netlink/specs/rt-neigh.yaml     |  2 +-
 Documentation/networking/ip-sysctl.rst        |  2 +-
 Documentation/networking/switchdev.rst        | 11 +++---
 net/core/neighbour.c                          | 26 ++++++++++----
 .../selftests/net/netfilter/nft_nat_zones.sh  | 34 +++++--------------
 5 files changed, 35 insertions(+), 40 deletions(-)

-- 
2.56.0.385.gd3acb90ef8-goog

[PATCH v1 net-next 1/4] Documentation: networking: switchdev: Replace arp_tbl with arp_table(net).

[Kuniyuki Iwashima]

Since commit cda2962b6e2b ("neighbour: Namespacify neigh_tables."),
arp_tbl is a template for the per-netns table.

Let's apply s/arp_tbl/arp_table(net)/ to switchdev.rst.

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
---
 Documentation/networking/switchdev.rst | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/Documentation/networking/switchdev.rst b/Documentation/networking/switchdev.rst
index 2966b7122f05..8e8ab6632ffe 100644
--- a/Documentation/networking/switchdev.rst
+++ b/Documentation/networking/switchdev.rst
@@ -401,14 +401,15 @@ The FIB entry's nexthop list contains the nexthop tuple (gateway, dev), but for
 the switch device to forward the packet with the correct dst mac address, the
 nexthop gateways must be resolved to the neighbor's mac address.  Neighbor mac
 address discovery comes via the ARP (or ND) process and is available via the
-arp_tbl neighbor table.  To resolve the routes nexthop gateways, the driver
-should trigger the kernel's neighbor resolution process.  See the rocker
+arp_table(net) neighbor table.  To resolve the routes nexthop gateways, the
+driver should trigger the kernel's neighbor resolution process.  See the rocker
 driver's rocker_port_ipv4_resolve() for an example.
 
-The driver can monitor for updates to arp_tbl using the netevent notifier
+The driver can monitor for updates to arp_table(net) using the netevent notifier
 NETEVENT_NEIGH_UPDATE.  The device can be programmed with resolved nexthops
-for the routes as arp_tbl updates.  The driver implements ndo_neigh_destroy
-to know when arp_tbl neighbor entries are purged from the port.
+for the routes as arp_table(net) updates.  The driver implements
+ndo_neigh_destroy to know when arp_table(net) neighbor entries are purged from
+the port.
 
 Device driver expected behavior
 -------------------------------
-- 
2.56.0.385.gd3acb90ef8-goog

[PATCH v1 net-next 2/4] selftests: netfilter: Set gc_thresh[123] for gw netns in nft_nat_zones.sh.

[Kuniyuki Iwashima]

Since commit cda2962b6e2b ("neighbour: Namespacify neigh_tables."),
net.ipv[46].neigh.default.gc_thresh[123] are per-netns attributes.

Let's update nft_nat_zones.sh.

Note that the number of neighbour entries does not even reach the
default gc_thresh1 (128) with the default maxclients=100, and the
raised thresholds are only needed for gw netns when maxclients is
manually increased (e.g., 2000 as mentioned in the comment).

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
---
Cc: Pablo Neira Ayuso <pablo@netfilter.org>
Cc: Florian Westphal <fw@strlen.de>
Cc: Phil Sutter <phil@nwl.cc>
---
 .../selftests/net/netfilter/nft_nat_zones.sh  | 34 +++++--------------
 1 file changed, 8 insertions(+), 26 deletions(-)

diff --git a/tools/testing/selftests/net/netfilter/nft_nat_zones.sh b/tools/testing/selftests/net/netfilter/nft_nat_zones.sh
index 9f200f80253a..d935c967dd13 100755
--- a/tools/testing/selftests/net/netfilter/nft_nat_zones.sh
+++ b/tools/testing/selftests/net/netfilter/nft_nat_zones.sh
@@ -31,25 +31,6 @@ ret=0
 #   NAT Gateway is supposed to do port reallocation for each of the
 #   connections.
 
-v4gc1=$(sysctl -n net.ipv4.neigh.default.gc_thresh1 2>/dev/null)
-v4gc2=$(sysctl -n net.ipv4.neigh.default.gc_thresh2 2>/dev/null)
-v4gc3=$(sysctl -n net.ipv4.neigh.default.gc_thresh3 2>/dev/null)
-v6gc1=$(sysctl -n net.ipv6.neigh.default.gc_thresh1 2>/dev/null)
-v6gc2=$(sysctl -n net.ipv6.neigh.default.gc_thresh2 2>/dev/null)
-v6gc3=$(sysctl -n net.ipv6.neigh.default.gc_thresh3 2>/dev/null)
-
-cleanup()
-{
-	cleanup_all_ns
-
-	sysctl -q net.ipv4.neigh.default.gc_thresh1="$v4gc1" 2>/dev/null
-	sysctl -q net.ipv4.neigh.default.gc_thresh2="$v4gc2" 2>/dev/null
-	sysctl -q net.ipv4.neigh.default.gc_thresh3="$v4gc3" 2>/dev/null
-	sysctl -q net.ipv6.neigh.default.gc_thresh1="$v6gc1" 2>/dev/null
-	sysctl -q net.ipv6.neigh.default.gc_thresh2="$v6gc2" 2>/dev/null
-	sysctl -q net.ipv6.neigh.default.gc_thresh3="$v6gc3" 2>/dev/null
-}
-
 checktool "nft --version" echo "run test without nft tool"
 checktool "conntrack -V" "run test without conntrack tool"
 
@@ -59,18 +40,19 @@ fi
 
 setup_ns gw srv
 
-trap cleanup EXIT
+trap cleanup_all_ns EXIT
 
 ip link add veth0 netns "$gw" type veth peer name eth0 netns "$srv"
 ip -net "$gw" link set veth0 up
 ip -net "$srv" link set eth0 up
 
-sysctl -q net.ipv6.neigh.default.gc_thresh1=512  2>/dev/null
-sysctl -q net.ipv6.neigh.default.gc_thresh2=1024 2>/dev/null
-sysctl -q net.ipv6.neigh.default.gc_thresh3=4096 2>/dev/null
-sysctl -q net.ipv4.neigh.default.gc_thresh1=512  2>/dev/null
-sysctl -q net.ipv4.neigh.default.gc_thresh2=1024 2>/dev/null
-sysctl -q net.ipv4.neigh.default.gc_thresh3=4096 2>/dev/null
+ip netns exec "$gw" sysctl -q \
+   net.ipv6.neigh.default.gc_thresh1=512 \
+   net.ipv6.neigh.default.gc_thresh2=1024 \
+   net.ipv6.neigh.default.gc_thresh3=4096 \
+   net.ipv4.neigh.default.gc_thresh1=512 \
+   net.ipv4.neigh.default.gc_thresh2=1024 \
+   net.ipv4.neigh.default.gc_thresh3=4096 2>/dev/null
 
 for i in $(seq 1 "$maxclients");do
   setup_ns "cl$i"
-- 
2.56.0.385.gd3acb90ef8-goog

[PATCH v1 net-next 3/4] neighbour: Schedule neigh_managed_work only when needed.

[Kuniyuki Iwashima]

neigh_table is now per-netns.

tbl->managed_work is scheduled when netns is created and runs
periodically even though the netns does not have any NTF_MANAGED
entries.

Let's delay scheduling the work for the first NTF_MANAGED entry
and stop rescheduling if tbl->managed_list is empty.

Suggested-by: Ido Schimmel <idosch@nvidia.com>
Link: https://lore.kernel.org/netdev/20260902143023.GA3966681@shredder/
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
---
 net/core/neighbour.c | 22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 90335895b415..6b0569aa5d64 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -184,6 +184,15 @@ static void neigh_update_gc_list(struct neighbour *n)
 	}
 }
 
+static void neigh_add_managed_list(struct neighbour *n)
+{
+	list_add_tail(&n->managed_list, &n->tbl->managed_list);
+
+	if (list_is_singular(&n->tbl->managed_list))
+		queue_delayed_work(system_power_efficient_wq,
+				   &n->tbl->managed_work, 0);
+}
+
 static void neigh_update_managed_list(struct neighbour *n)
 {
 	bool on_managed_list, add_to_managed;
@@ -194,7 +203,7 @@ static void neigh_update_managed_list(struct neighbour *n)
 	if (!add_to_managed && on_managed_list)
 		list_del_init(&n->managed_list);
 	else if (add_to_managed && !on_managed_list)
-		list_add_tail(&n->managed_list, &n->tbl->managed_list);
+		neigh_add_managed_list(n);
 }
 
 static void neigh_update_flags(struct neighbour *neigh, u32 flags, int *notify,
@@ -708,7 +717,7 @@ ___neigh_create(struct neigh_table *tbl, const void *pkey,
 	if (!exempt_from_gc)
 		list_add_tail(&n->gc_list, &n->tbl->gc_list);
 	if (n->flags & NTF_MANAGED)
-		list_add_tail(&n->managed_list, &n->tbl->managed_list);
+		neigh_add_managed_list(n);
 	if (want_ref)
 		neigh_hold(n);
 	hlist_add_head_rcu(&n->hash, &nht->hash_heads[hash_val]);
@@ -1670,10 +1679,14 @@ static void neigh_managed_work(struct work_struct *work)
 	struct neighbour *neigh;
 
 	spin_lock_bh(&tbl->lock);
+
 	list_for_each_entry(neigh, &tbl->managed_list, managed_list)
 		neigh_event_send_probe(neigh, NULL, false);
-	queue_delayed_work(system_power_efficient_wq, &tbl->managed_work,
-			   NEIGH_VAR(&tbl->parms, INTERVAL_PROBE_TIME_MS));
+
+	if (!list_empty(&tbl->managed_list))
+		queue_delayed_work(system_power_efficient_wq, &tbl->managed_work,
+				   NEIGH_VAR(&tbl->parms, INTERVAL_PROBE_TIME_MS));
+
 	spin_unlock_bh(&tbl->lock);
 }
 
@@ -1873,7 +1886,6 @@ static int neigh_table_init(struct net *net, struct neigh_table *tbl)
 
 	INIT_LIST_HEAD(&tbl->managed_list);
 	INIT_DEFERRABLE_WORK(&tbl->managed_work, neigh_managed_work);
-	queue_delayed_work(system_power_efficient_wq, &tbl->managed_work, 0);
 
 	return 0;
 
-- 
2.56.0.385.gd3acb90ef8-goog

[PATCH v1 net-next 4/4] neighbour: Floor INTERVAL_PROBE_TIME_MS at 1000.

[Kuniyuki Iwashima]

Previously, the lower bound of INTERVAL_PROBE_TIME_MS was capped
at 1s by commit ed6cd6a17896 ("net, neigh: Set lower cap for
neigh_managed_work rearming").

Later, commit 211da42eaa45 ("net, neigh: introduce
interval_probe_time_ms for periodic probe") changed the limit
to 1ms.

The limit actually did not work but was fixed with
netlink_range_validation by commit 6d79b223ec44 ("neighbour:
Enforce min/max to NDTPA_INTERVAL_PROBE_TIME_MS.").

neigh_table is now per-netns, and a user could hog CPU by setting
INTERVAL_PROBE_TIME_MS to a small value.

Let's floor the value at 1 second.

Suggested-by: Ido Schimmel <idosch@nvidia.com>
Link: https://lore.kernel.org/netdev/20260902143023.GA3966681@shredder/
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
---
 Documentation/netlink/specs/rt-neigh.yaml | 2 +-
 Documentation/networking/ip-sysctl.rst    | 2 +-
 net/core/neighbour.c                      | 4 ++--
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/Documentation/netlink/specs/rt-neigh.yaml b/Documentation/netlink/specs/rt-neigh.yaml
index c8e55c98d564..7929e667cc7a 100644
--- a/Documentation/netlink/specs/rt-neigh.yaml
+++ b/Documentation/netlink/specs/rt-neigh.yaml
@@ -342,7 +342,7 @@ attribute-sets:
         name: interval-probe-time-ms
         type: u64
         checks:
-          min: 1
+          min: 1000
           max: 86400000
 
 operations:
diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
index 685c84cf543d..b00bd77363d7 100644
--- a/Documentation/networking/ip-sysctl.rst
+++ b/Documentation/networking/ip-sysctl.rst
@@ -248,7 +248,7 @@ neigh/default/unres_qlen - INTEGER
 
 neigh/default/interval_probe_time_ms - INTEGER
 	The probe interval for neighbor entries with NTF_MANAGED flag,
-	the min value is 1, and the max value is 86400000 (1 day).
+	the min value is 1000 (1s), and the max value is 86400000 (1 day).
 
 	Default: 5000
 
diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 6b0569aa5d64..92e3c83c0fe5 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -2438,7 +2438,7 @@ static const struct nla_policy nl_neightbl_policy[NDTA_MAX+1] = {
 #define NTBL_PARM_MS_MAX	(24 * 60 * 60 * MSEC_PER_SEC)
 
 static const struct netlink_range_validation nl_ntbl_parm_ms_range = {
-	.min = 1,
+	.min = 1000,
 	.max = NTBL_PARM_MS_MAX,
 };
 
@@ -3701,7 +3701,7 @@ static int neigh_proc_dointvec_ms_jiffies_positive(const struct ctl_table *ctl,
 	struct ctl_table tmp = *ctl;
 	int ret, min, max;
 
-	min = msecs_to_jiffies(1);
+	min = HZ;
 	max = msecs_to_jiffies(NTBL_PARM_MS_MAX);
 
 	tmp.extra1 = &min;
-- 
2.56.0.385.gd3acb90ef8-goog

Re: [PATCH v1 net-next 0/4] neighbour: Misc follow-ups on per-netns neigh_table series.

[Ido Schimmel]

On Mon, Oct 12, 2026 at 07:44:55PM +0000, Kuniyuki Iwashima wrote:
> Patch 1 updates the switchdev doc, s/arp_tbl/arp_table(net)/.
> 
> Patch 2 updates a selftest for per-netns sysctl knobs, though this
> is not an actual issue since the test does not hit gc_thresh by
> default.
> 
> Patches 3 & 4 are based on a suggestion by Ido Schimmel to make
> neigh_managed_work CPU-friendly:
> 
>   https://lore.kernel.org/netdev/20260902143023.GA3966681@shredder/

Thanks for the follow-up, but I think you missed my first point... My
comment was about the GC work that doesn't have a floor at all. An
unprivileged user can set the base reachable time to 0 and
neigh_periodic_work() will hog the CPU.

> 
> Given it's rc7, I'll defer RTNL removal to the next cycle.
> 
> 
> Kuniyuki Iwashima (4):
>   Documentation: networking: switchdev: Replace arp_tbl with
>     arp_table(net).
>   selftests: netfilter: Set gc_thresh[123] for gw netns in
>     nft_nat_zones.sh.
>   neighbour: Schedule neigh_managed_work only when needed.
>   neighbour: Floor INTERVAL_PROBE_TIME_MS at 1000.
> 
>  Documentation/netlink/specs/rt-neigh.yaml     |  2 +-
>  Documentation/networking/ip-sysctl.rst        |  2 +-
>  Documentation/networking/switchdev.rst        | 11 +++---
>  net/core/neighbour.c                          | 26 ++++++++++----
>  .../selftests/net/netfilter/nft_nat_zones.sh  | 34 +++++--------------
>  5 files changed, 35 insertions(+), 40 deletions(-)
> 
> -- 
> 2.56.0.385.gd3acb90ef8-goog
> 

Re: [PATCH v1 net-next 4/4] neighbour: Floor INTERVAL_PROBE_TIME_MS at 1000.

[Ido Schimmel]

On Mon, Oct 12, 2026 at 07:44:59PM +0000, Kuniyuki Iwashima wrote:
> Previously, the lower bound of INTERVAL_PROBE_TIME_MS was capped
> at 1s by commit ed6cd6a17896 ("net, neigh: Set lower cap for
> neigh_managed_work rearming").

Nit: INTERVAL_PROBE_TIME_MS didn't exist in ed6cd6a17896. It was only
introduced later, in 211da42eaa45.

> 
> Later, commit 211da42eaa45 ("net, neigh: introduce
> interval_probe_time_ms for periodic probe") changed the limit
> to 1ms.
> 
> The limit actually did not work but was fixed with
> netlink_range_validation by commit 6d79b223ec44 ("neighbour:
> Enforce min/max to NDTPA_INTERVAL_PROBE_TIME_MS.").
> 
> neigh_table is now per-netns, and a user could hog CPU by setting
> INTERVAL_PROBE_TIME_MS to a small value.
> 
> Let's floor the value at 1 second.

The bot will most likely complain that this changes existing behavior,
but:

1. The original floor was 1 second.

2. It is unlikely that anyone but syzbot is setting it below 1 second.

I would explain this in the commit message to suppress such comments.

Re: [PATCH v1 net-next 0/4] neighbour: Misc follow-ups on per-netns neigh_table series.

[Kuniyuki Iwashima]

On Tue, Oct 13, 2026 at 12:00 AM Ido Schimmel <idosch@nvidia.com> wrote:
>
> On Mon, Oct 12, 2026 at 07:44:55PM +0000, Kuniyuki Iwashima wrote:
> > Patch 1 updates the switchdev doc, s/arp_tbl/arp_table(net)/.
> >
> > Patch 2 updates a selftest for per-netns sysctl knobs, though this
> > is not an actual issue since the test does not hit gc_thresh by
> > default.
> >
> > Patches 3 & 4 are based on a suggestion by Ido Schimmel to make
> > neigh_managed_work CPU-friendly:
> >
> >   https://lore.kernel.org/netdev/20260902143023.GA3966681@shredder/
>
> Thanks for the follow-up, but I think you missed my first point...

Oops, sorry I seem to have been sidetracked by 6d79b223ec44 series...

> My
> comment was about the GC work that doesn't have a floor at all. An
> unprivileged user can set the base reachable time to 0 and
> neigh_periodic_work() will hog the CPU.

I'll add the max(HZ, ...) change in patch 5.

---
pw-bot: cr



>
> >
> > Given it's rc7, I'll defer RTNL removal to the next cycle.
> >
> >
> > Kuniyuki Iwashima (4):
> >   Documentation: networking: switchdev: Replace arp_tbl with
> >     arp_table(net).
> >   selftests: netfilter: Set gc_thresh[123] for gw netns in
> >     nft_nat_zones.sh.
> >   neighbour: Schedule neigh_managed_work only when needed.
> >   neighbour: Floor INTERVAL_PROBE_TIME_MS at 1000.
> >
> >  Documentation/netlink/specs/rt-neigh.yaml     |  2 +-
> >  Documentation/networking/ip-sysctl.rst        |  2 +-
> >  Documentation/networking/switchdev.rst        | 11 +++---
> >  net/core/neighbour.c                          | 26 ++++++++++----
> >  .../selftests/net/netfilter/nft_nat_zones.sh  | 34 +++++--------------
> >  5 files changed, 35 insertions(+), 40 deletions(-)
> >
> > --
> > 2.56.0.385.gd3acb90ef8-goog
> >

Re: [PATCH v1 net-next 4/4] neighbour: Floor INTERVAL_PROBE_TIME_MS at 1000.

[Kuniyuki Iwashima]

On Tue, Oct 13, 2026 at 12:16 AM Ido Schimmel <idosch@nvidia.com> wrote:
>
> On Mon, Oct 12, 2026 at 07:44:59PM +0000, Kuniyuki Iwashima wrote:
> > Previously, the lower bound of INTERVAL_PROBE_TIME_MS was capped
> > at 1s by commit ed6cd6a17896 ("net, neigh: Set lower cap for
> > neigh_managed_work rearming").
>
> Nit: INTERVAL_PROBE_TIME_MS didn't exist in ed6cd6a17896. It was only
> introduced later, in 211da42eaa45.

Indeed, I'll rephrase that with neigh_managed_work().

>
> >
> > Later, commit 211da42eaa45 ("net, neigh: introduce
> > interval_probe_time_ms for periodic probe") changed the limit
> > to 1ms.
> >
> > The limit actually did not work but was fixed with
> > netlink_range_validation by commit 6d79b223ec44 ("neighbour:
> > Enforce min/max to NDTPA_INTERVAL_PROBE_TIME_MS.").
> >
> > neigh_table is now per-netns, and a user could hog CPU by setting
> > INTERVAL_PROBE_TIME_MS to a small value.
> >
> > Let's floor the value at 1 second.
>
> The bot will most likely complain that this changes existing behavior,
> but:
>
> 1. The original floor was 1 second.
>
> 2. It is unlikely that anyone but syzbot is setting it below 1 second.
>
> I would explain this in the commit message to suppress such comments.

Will add them in v2.

Thank you !