Commit 707ec627 authored by Jakub Kicinski's avatar Jakub Kicinski
Browse files

Merge branch 'net-reduce-rtnl-pressure-in-unregister_netdevice' 

Eric Dumazet says:

====================
net: reduce RTNL pressure in unregister_netdevice()

One major source of RTNL contention resides in unregister_netdevice()

Due to RCU protection of various network structures, and
unregister_netdevice() being a synchronous function,
it is calling potentially slow functions while holding RTNL.

I think we can release RTNL in two points, so that three
slow functions are called while RTNL can be used
by other threads.

v1: https://lore.kernel.org/netdev/20250107130906.098fc8d6@kernel.org/T/#m398c95f5778e1ff70938e079d3c4c43c050ad2a6
====================

Link: https://patch.msgid.link/20250114205531.967841-1-edumazet@google.com


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parents bc1e64d5 83419b61

include/net/net_namespace.h

+2 −0
Original line number Diff line number Diff line
@@ -210,6 +210,8 @@ void net_ns_barrier(void); 


struct ns_common *get_net_ns(struct ns_common *ns);

struct net *get_net_ns_by_fd(int fd);

extern struct task_struct *cleanup_net_task;



#else /* CONFIG_NET_NS */

#include <linux/sched.h>

#include <linux/nsproxy.h>

net/core/dev.c

+75 −22
Original line number Diff line number Diff line
@@ -6124,8 +6124,6 @@ void netif_receive_skb_list(struct list_head *head) 
}

EXPORT_SYMBOL(netif_receive_skb_list);



static DEFINE_PER_CPU(struct work_struct, flush_works);



/* Network device is going away, flush any packets still pending */

static void flush_backlog(struct work_struct *work)

{
@@ -6182,36 +6180,54 @@ static bool flush_required(int cpu) 
	return true;

}



struct flush_backlogs {

	cpumask_t		flush_cpus;

	struct work_struct	w[];

};



static struct flush_backlogs *flush_backlogs_alloc(void)

{

	return kmalloc(struct_size_t(struct flush_backlogs, w, nr_cpu_ids),

		       GFP_KERNEL);

}



static struct flush_backlogs *flush_backlogs_fallback;

static DEFINE_MUTEX(flush_backlogs_mutex);



static void flush_all_backlogs(void)

{

	static cpumask_t flush_cpus;

	struct flush_backlogs *ptr = flush_backlogs_alloc();

	unsigned int cpu;



	/* since we are under rtnl lock protection we can use static data

	 * for the cpumask and avoid allocating on stack the possibly

	 * large mask

	 */

	ASSERT_RTNL();

	if (!ptr) {

		mutex_lock(&flush_backlogs_mutex);

		ptr = flush_backlogs_fallback;

	}

	cpumask_clear(&ptr->flush_cpus);



	cpus_read_lock();



	cpumask_clear(&flush_cpus);

	for_each_online_cpu(cpu) {

		if (flush_required(cpu)) {

			queue_work_on(cpu, system_highpri_wq,

				      per_cpu_ptr(&flush_works, cpu));

			cpumask_set_cpu(cpu, &flush_cpus);

			INIT_WORK(&ptr->w[cpu], flush_backlog);

			queue_work_on(cpu, system_highpri_wq, &ptr->w[cpu]);

			__cpumask_set_cpu(cpu, &ptr->flush_cpus);

		}

	}



	/* we can have in flight packet[s] on the cpus we are not flushing,

	 * synchronize_net() in unregister_netdevice_many() will take care of

	 * them

	 * them.

	 */

	for_each_cpu(cpu, &flush_cpus)

		flush_work(per_cpu_ptr(&flush_works, cpu));

	for_each_cpu(cpu, &ptr->flush_cpus)

		flush_work(&ptr->w[cpu]);



	cpus_read_unlock();



	if (ptr != flush_backlogs_fallback)

		kfree(ptr);

	else

		mutex_unlock(&flush_backlogs_mutex);

}



static void net_rps_send_ipi(struct softnet_data *remsd)
@@ -10244,14 +10260,46 @@ static void dev_index_release(struct net *net, int ifindex) 
	WARN_ON(xa_erase(&net->dev_by_index, ifindex));

}



static bool from_cleanup_net(void)

{

#ifdef CONFIG_NET_NS

	return current == cleanup_net_task;

#else

	return false;

#endif

}



static void rtnl_drop_if_cleanup_net(void)

{

	if (from_cleanup_net())

		__rtnl_unlock();

}



static void rtnl_acquire_if_cleanup_net(void)

{

	if (from_cleanup_net())

		rtnl_lock();

}



/* Delayed registration/unregisteration */

LIST_HEAD(net_todo_list);

static LIST_HEAD(net_todo_list_for_cleanup_net);



/* TODO: net_todo_list/net_todo_list_for_cleanup_net should probably

 * be provided by callers, instead of being static, rtnl protected.

 */

static struct list_head *todo_list(void)

{

	return from_cleanup_net() ? &net_todo_list_for_cleanup_net :

				    &net_todo_list;

}



DECLARE_WAIT_QUEUE_HEAD(netdev_unregistering_wq);

atomic_t dev_unreg_count = ATOMIC_INIT(0);



static void net_set_todo(struct net_device *dev)

{

	list_add_tail(&dev->todo_list, &net_todo_list);

	list_add_tail(&dev->todo_list, todo_list());

}



static netdev_features_t netdev_sync_upper_features(struct net_device *lower,
@@ -11101,7 +11149,7 @@ void netdev_run_todo(void) 
#endif



	/* Snapshot list, allow later requests */

	list_replace_init(&net_todo_list, &list);

	list_replace_init(todo_list(), &list);



	__rtnl_unlock();
@@ -11623,7 +11671,7 @@ EXPORT_SYMBOL_GPL(alloc_netdev_dummy); 
void synchronize_net(void)

{

	might_sleep();

	if (rtnl_is_locked())

	if (from_cleanup_net() || rtnl_is_locked())

		synchronize_rcu_expedited();

	else

		synchronize_rcu();
@@ -11728,9 +11776,11 @@ void unregister_netdevice_many_notify(struct list_head *head, 
		WRITE_ONCE(dev->reg_state, NETREG_UNREGISTERING);

		netdev_unlock(dev);

	}

	flush_all_backlogs();



	rtnl_drop_if_cleanup_net();

	flush_all_backlogs();

	synchronize_net();

	rtnl_acquire_if_cleanup_net();



	list_for_each_entry(dev, head, unreg_list) {

		struct sk_buff *skb = NULL;
@@ -11790,7 +11840,9 @@ void unregister_netdevice_many_notify(struct list_head *head, 
#endif

	}



	rtnl_drop_if_cleanup_net();

	synchronize_net();

	rtnl_acquire_if_cleanup_net();



	list_for_each_entry(dev, head, unreg_list) {

		netdev_put(dev, &dev->dev_registered_tracker);
@@ -12455,12 +12507,13 @@ static int __init net_dev_init(void) 
	 *	Initialise the packet receive queues.

	 */



	flush_backlogs_fallback = flush_backlogs_alloc();

	if (!flush_backlogs_fallback)

		goto out;



	for_each_possible_cpu(i) {

		struct work_struct *flush = per_cpu_ptr(&flush_works, i);

		struct softnet_data *sd = &per_cpu(softnet_data, i);



		INIT_WORK(flush, flush_backlog);



		skb_queue_head_init(&sd->input_pkt_queue);

		skb_queue_head_init(&sd->process_queue);

#ifdef CONFIG_XFRM_OFFLOAD

net/core/net_namespace.c

+5 −0
Original line number Diff line number Diff line
@@ -588,6 +588,8 @@ static void unhash_nsid(struct net *net, struct net *last) 


static LLIST_HEAD(cleanup_list);



struct task_struct *cleanup_net_task;



static void cleanup_net(struct work_struct *work)

{

	const struct pernet_operations *ops;
@@ -596,6 +598,8 @@ static void cleanup_net(struct work_struct *work) 
	LIST_HEAD(net_exit_list);

	LIST_HEAD(dev_kill_list);



	cleanup_net_task = current;



	/* Atomically snapshot the list of namespaces to cleanup */

	net_kill_list = llist_del_all(&cleanup_list);
@@ -670,6 +674,7 @@ static void cleanup_net(struct work_struct *work) 
		put_user_ns(net->user_ns);

		net_free(net);

	}

	cleanup_net_task = NULL;

}



/**