Commit 8a2b61e9 authored by Eric Dumazet's avatar Eric Dumazet Committed by Jakub Kicinski
Browse files

net: no longer assume RTNL is held in flush_all_backlogs() 



flush_all_backlogs() uses per-cpu and static data to hold its
temporary data, on the assumption it is called under RTNL
protection.

Following patch in the series will break this assumption.

Use instead a dynamically allocated piece of memory.

In the unlikely case the allocation fails,
use a boot-time allocated memory.

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Reviewed-by: default avatarJesse Brandeburg <jbrandeburg@cloudflare.com>
Link: https://patch.msgid.link/20250114205531.967841-3-edumazet@google.com


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 0734d7c3

net/core/dev.c

+35 −18
Original line number Diff line number Diff line
@@ -6013,8 +6013,6 @@ 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)

{
@@ -6071,36 +6069,54 @@ 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)
@@ -12313,12 +12329,13 @@ 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