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ipv4: Batch rt_flush_dev() in netdev_run_todo().

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IPv4 uncached routes are linked to the global per-cpu lists,
rt_uncached_list.

When unregistering a netdev, rt_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.

Note that rt_flush_dev() must be called after setting dev->reg_state
to NETREG_UNREGISTERED.  Otherwise, because rt_flush_dev(NULL) runs
without RTNL, it could race with unregister_netdevice_many_notify()
and prematurely purge routes for NETREG_UNREGISTERING dev, for
which flush_all_backlogs() has not been called yet.

Reported-by: Chris J Arges <carges@cloudflare.com>
Closes: https://lore.kernel.org/netdev/20260917-hash-bucket-route-lists-v3-0-30493a37b6eb@cloudflare.com/
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Tested-by: Chris J Arges <carges@cloudflare.com>
Link: https://patch.msgid.link/20261001204752.2572265-6-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Kuniyuki Iwashima 2026-10-01 20:47:17 +00:00 committed by Jakub Kicinski
parent 4eb2e2f358
commit ca68547990
3 changed files with 19 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
include/net/route.h
View File

@ -129,7 +129,13 @@ struct in_device;
int ip_rt_init(void);
void rt_cache_flush(struct net *net);
#ifdef CONFIG_INET
void rt_flush_dev(struct net_device *dev);
#else
static inline void rt_flush_dev(struct net_device *dev)
{
}
#endif
static inline void inet_sk_init_flowi4(const struct inet_sock *inet,
struct flowi4 *fl4)

4
net/core/dev.c
View File

@ -129,6 +129,7 @@
#include <linux/ip.h>
#include <net/ip.h>
#include <net/mpls.h>
#include <net/route.h>
#include <linux/ipv6.h>
#include <linux/in.h>
#include <linux/jhash.h>
@ -11886,6 +11887,9 @@ void netdev_run_todo(void)
linkwatch_sync_dev(dev);
}
if (!list_empty(&list))
rt_flush_dev(NULL);
cnt = 0;
while (!list_empty(&list)) {
dev = netdev_wait_allrefs_any(&list);

11
net/ipv4/route.c
View File

@ -1587,6 +1587,9 @@ void rt_flush_dev(struct net_device *dev)
struct rtable *rt, *safe;
int cpu;
if (dev && dev->dismantle)
return;
for_each_possible_cpu(cpu) {
struct uncached_list *ul = &per_cpu(rt_uncached_list, cpu);
@ -1595,10 +1598,14 @@ void rt_flush_dev(struct net_device *dev)
spin_lock_bh(&ul->lock);
list_for_each_entry_safe(rt, safe, &ul->head, dst.rt_uncached) {
if (rt->dst.dev != dev)
struct net_device *rt_dev = rt->dst.dev;
if (dev ? rt_dev != dev :
READ_ONCE(rt_dev->reg_state) != NETREG_UNREGISTERED)
continue;
rcu_assign_pointer(rt->dst.dev_rcu, blackhole_netdev);
netdev_ref_replace(dev, blackhole_netdev,
netdev_ref_replace(rt_dev, blackhole_netdev,
&rt->dst.dev_tracker, GFP_ATOMIC);
list_del_init(&rt->dst.rt_uncached);
}