net/core/gro_cells.c

// SPDX-License-Identifier: GPL-2.0
#include <linux/skbuff.h>
#include <linux/slab.h>
#include <linux/netdevice.h>
#include <net/gro_cells.h>
#include <net/hotdata.h>

struct gro_cell {
	struct sk_buff_head	napi_skbs;
	struct napi_struct	napi;
	local_lock_t		bh_lock;
};

int gro_cells_receive(struct gro_cells *gcells, struct sk_buff *skb)
{
	struct net_device *dev = skb->dev;
	bool have_bh_lock = false;
	struct gro_cell *cell;
	int res;

	rcu_read_lock();
	if (unlikely(!(dev->flags & IFF_UP)))
		goto drop;

	skb_unset_transport_header(skb);

	if (!gcells->cells || skb_cloned(skb) || netif_elide_gro(dev)) {
		res = netif_rx(skb);
		goto unlock;
	}

	local_lock_nested_bh(&gcells->cells->bh_lock);
	have_bh_lock = true;
	cell = this_cpu_ptr(gcells->cells);

	if (skb_queue_len(&cell->napi_skbs) > READ_ONCE(net_hotdata.max_backlog)) {
drop:
		dev_core_stats_rx_dropped_inc(dev);
		kfree_skb(skb);
		res = NET_RX_DROP;
		goto unlock;
	}

	__skb_queue_tail(&cell->napi_skbs, skb);
	if (skb_queue_len(&cell->napi_skbs) == 1)
		napi_schedule(&cell->napi);

	res = NET_RX_SUCCESS;

unlock:
	if (have_bh_lock)
		local_unlock_nested_bh(&gcells->cells->bh_lock);
	rcu_read_unlock();
	return res;
}
EXPORT_SYMBOL(gro_cells_receive);

/* called under BH context */
static int gro_cell_poll(struct napi_struct *napi, int budget)
{
	struct gro_cell *cell = container_of(napi, struct gro_cell, napi);
	struct sk_buff *skb;
	int work_done = 0;

	while (work_done < budget) {
		__local_lock_nested_bh(&cell->bh_lock);
		skb = __skb_dequeue(&cell->napi_skbs);
		__local_unlock_nested_bh(&cell->bh_lock);
		if (!skb)
			break;
		napi_gro_receive(napi, skb);
		work_done++;
	}

	if (work_done < budget)
		napi_complete_done(napi, work_done);
	return work_done;
}

int gro_cells_init(struct gro_cells *gcells, struct net_device *dev)
{
	int i;

	gcells->cells = alloc_percpu(struct gro_cell);
	if (!gcells->cells)
		return -ENOMEM;

	for_each_possible_cpu(i) {
		struct gro_cell *cell = per_cpu_ptr(gcells->cells, i);

		__skb_queue_head_init(&cell->napi_skbs);
		local_lock_init(&cell->bh_lock);

		set_bit(NAPI_STATE_NO_BUSY_POLL, &cell->napi.state);

		netif_napi_add(dev, &cell->napi, gro_cell_poll);
		napi_enable(&cell->napi);
	}
	return 0;
}
EXPORT_SYMBOL(gro_cells_init);

struct percpu_free_defer {
	struct rcu_head rcu;
	void __percpu	*ptr;
};

static void percpu_free_defer_callback(struct rcu_head *head)
{
	struct percpu_free_defer *defer;

	defer = container_of(head, struct percpu_free_defer, rcu);
	free_percpu(defer->ptr);
	kfree(defer);
}

void gro_cells_destroy(struct gro_cells *gcells)
{
	struct percpu_free_defer *defer;
	int i;

	if (!gcells->cells)
		return;
	for_each_possible_cpu(i) {
		struct gro_cell *cell = per_cpu_ptr(gcells->cells, i);

		napi_disable(&cell->napi);
		__netif_napi_del(&cell->napi);
		__skb_queue_purge(&cell->napi_skbs);
	}
	/* We need to observe an rcu grace period before freeing ->cells,
	 * because netpoll could access dev->napi_list under rcu protection.
	 * Try hard using call_rcu() instead of synchronize_rcu(),
	 * because we might be called from cleanup_net(), and we
	 * definitely do not want to block this critical task.
	 */
	defer = kmalloc_obj(*defer, GFP_KERNEL | __GFP_NOWARN);
	if (likely(defer)) {
		defer->ptr = gcells->cells;
		call_rcu(&defer->rcu, percpu_free_defer_callback);
	} else {
		/* We do not hold RTNL at this point, synchronize_net()
		 * would not be able to expedite this sync.
		 */
		synchronize_rcu_expedited();
		free_percpu(gcells->cells);
	}
	gcells->cells = NULL;
}
EXPORT_SYMBOL(gro_cells_destroy);