[PATCH v3 net-next 6/6] ipv6: Batch rt6_uncached_list_flush_dev() in netdev_run_todo().
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WARM1d
From: Kuniyuki Iwashima <kuniyu@google.com>
Date: 2026-10-01 20:48:01
Subsystem:
networking [general], networking [ipv4/ipv6], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, David Ahern, Ido Schimmel, Linus Torvalds
IPv6 uncached routes are linked to the global per-cpu lists,
rt6_uncached_list.
When unregistering a netdev, rt6_uncached_list_flush_dev() iterates
over the potentially long lists to find uncached routes tied to
the device and swap it with blackhole_netdev.
Since it is called for every device in dying netns under RTNL,
it adds O(N_dev x (N_cpu + N_route)) costs to any batched device
unregistration.
Let's call it once per batched device unregistration without RTNL.
Because it now runs without RTNL, rt->dst.dev and rt->rt6i_idev->dev
may transition to NETREG_UNREGISTERED at different times. Thus, we
must check that both devices are blackhole_netdev before unlinking
the route; otherwise, the remaining device reference would not be
flushed when the other device is unregistered.
In addition, since netdev_run_todo() runs even when IPv6 is disabled,
rt6_uncached_list_flush_dev() must check ipv6_mod_enabled() before
touching rt6_uncached_list.
Note also that netdev_run_todo() cannot be called before
rt6_uncached_list is initialised because:
1. unregister_netdevice_many_notify() panics when
dev_boot_phase == 1 (net_dev_init() is subsys_initcall()).
2. the only device registered before fs_initcall_sync() is
loopback and loopback_net_init() panics in case of failure.
Reported-by: Chris J Arges <redacted>
Closes: https://lore.kernel.org/netdev/20260917-hash-bucket-route-lists-v3-0-30493a37b6eb@cloudflare.com/ (local)
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
---
v3:
* Unlink only when both devices are blackhole_netdev
* Clarify netdev_run_todo() does not run before
rt6_uncached_list is initialised
* Fix CONFIG_IPV6=n build
---
include/net/ip6_route.h | 7 +++++++
net/core/dev.c | 5 ++++-
net/ipv6/route.c | 24 ++++++++++++++++--------
3 files changed, 27 insertions(+), 9 deletions(-)
diff --git a/include/net/ip6_route.h b/include/net/ip6_route.h
index 0f9b7a260d25..b9de335b639a 100644
--- a/include/net/ip6_route.h
+++ b/include/net/ip6_route.h@@ -231,6 +231,13 @@ void rt6_multipath_rebalance(struct fib6_info *f6i); void rt6_uncached_list_add(struct rt6_info *rt); void rt6_uncached_list_del(struct rt6_info *rt); +#ifdef CONFIG_IPV6 +void rt6_uncached_list_flush_dev(struct net_device *dev); +#else +static inline void rt6_uncached_list_flush_dev(struct net_device *dev) +{ +} +#endif static inline const struct rt6_info *skb_rt6_info(const struct sk_buff *skb) {
diff --git a/net/core/dev.c b/net/core/dev.c
index 7dba0292f052..12a0e7d6567b 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c@@ -131,6 +131,7 @@ #include <net/mpls.h> #include <net/route.h> #include <linux/ipv6.h> +#include <net/ip6_route.h> #include <linux/in.h> #include <linux/jhash.h> #include <linux/random.h>
@@ -11839,8 +11840,10 @@ void netdev_run_todo(void) linkwatch_sync_dev(dev); } - if (!list_empty(&list)) + if (!list_empty(&list)) { rt_flush_dev(NULL); + rt6_uncached_list_flush_dev(NULL); + } cnt = 0; while (!list_empty(&list)) {
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index a76869ff87cd..b1dcb5e5da88 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c@@ -158,10 +158,16 @@ void rt6_uncached_list_del(struct rt6_info *rt) } } -static void rt6_uncached_list_flush_dev(struct net_device *dev) +void rt6_uncached_list_flush_dev(struct net_device *dev) { int cpu; + if (!ipv6_mod_enabled()) + return; + + if (dev && dev->dismantle) + return; + for_each_possible_cpu(cpu) { struct uncached_list *ul = per_cpu_ptr(&rt6_uncached_list, cpu); struct rt6_info *rt, *safe;
@@ -173,22 +179,24 @@ static void rt6_uncached_list_flush_dev(struct net_device *dev) list_for_each_entry_safe(rt, safe, &ul->head, dst.rt_uncached) { struct inet6_dev *rt_idev = rt->rt6i_idev; struct net_device *rt_dev = rt->dst.dev; - bool handled = false; - if (rt_idev && rt_idev->dev == dev) { + if (rt_idev && + (dev ? rt_idev->dev == dev : + READ_ONCE(rt_idev->dev->reg_state) == NETREG_UNREGISTERED)) { rt->rt6i_idev = in6_dev_get(blackhole_netdev); in6_dev_put(rt_idev); - handled = true; } - if (rt_dev == dev) { - rt->dst.dev = blackhole_netdev; + if (dev ? rt_dev == dev : + READ_ONCE(rt_dev->reg_state) == NETREG_UNREGISTERED) { + rcu_assign_pointer(rt->dst.dev_rcu, blackhole_netdev); netdev_ref_replace(rt_dev, blackhole_netdev, &rt->dst.dev_tracker, GFP_ATOMIC); - handled = true; } - if (handled) + + if (rt->dst.dev == blackhole_netdev && + (!rt->rt6i_idev || rt->rt6i_idev->dev == blackhole_netdev)) list_del_init(&rt->dst.rt_uncached); } spin_unlock_bh(&ul->lock);
--
2.56.0.rc1.315.gc6ed9934b7-goog