/*
 * Common framework for low-level network console, dump, and debugger code
 *
 * Sep 8 2003  Matt Mackall <mpm@selenic.com>
 *
 * based on the netconsole code from:
 *
 * Copyright (C) 2001  Ingo Molnar <mingo@redhat.com>
 * Copyright (C) 2002  Red Hat, Inc.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/moduleparam.h>
#include <linux/kernel.h>
#include <linux/netdevice.h>
#include <linux/etherdevice.h>
#include <linux/string.h>
#include <linux/if_arp.h>
#include <linux/inetdevice.h>
#include <linux/inet.h>
#include <linux/interrupt.h>
#include <linux/netpoll.h>
#include <linux/sched.h>
#include <linux/delay.h>
#include <linux/rcupdate.h>
#include <linux/workqueue.h>
#include <linux/slab.h>
#include <linux/export.h>
#include <linux/if_vlan.h>
#include <net/tcp.h>
#include <net/udp.h>
#include <net/addrconf.h>
#include <net/ndisc.h>
#include <net/ip6_checksum.h>
#include <asm/unaligned.h>
#include <trace/events/napi.h>

/*
 * We maintain a small pool of fully-sized skbs, to make sure the
 * message gets out even in extreme OOM situations.
 */

#define MAX_UDP_CHUNK 1460
#define MAX_SKBS 32

static struct sk_buff_head skb_pool;

DEFINE_STATIC_SRCU(netpoll_srcu);

#define USEC_PER_POLL   50

#define MAX_SKB_SIZE                                                    \
        (sizeof(struct ethhdr) +                                        \
         sizeof(struct iphdr) +                                         \
         sizeof(struct udphdr) +                                        \
         MAX_UDP_CHUNK)

static void zap_completion_queue(void);
static void netpoll_async_cleanup(struct work_struct *work);

static unsigned int carrier_timeout = 4;
module_param(carrier_timeout, uint, 0644);

#define np_info(np, fmt, ...)                           \
        pr_info("%s: " fmt, np->name, ##__VA_ARGS__)
#define np_err(np, fmt, ...)                            \
        pr_err("%s: " fmt, np->name, ##__VA_ARGS__)
#define np_notice(np, fmt, ...)                         \
        pr_notice("%s: " fmt, np->name, ##__VA_ARGS__)

static int netpoll_start_xmit(struct sk_buff *skb, struct net_device *dev,
                              struct netdev_queue *txq)
{
        int status = NETDEV_TX_OK;
        netdev_features_t features;

        features = netif_skb_features(skb);

        if (skb_vlan_tag_present(skb) &&
            !vlan_hw_offload_capable(features, skb->vlan_proto)) {
                skb = __vlan_hwaccel_push_inside(skb);
                if (unlikely(!skb)) {
                        /* This is actually a packet drop, but we
                         * don't want the code that calls this
                         * function to try and operate on a NULL skb.
                         */
                        goto out;
                }
        }

        status = netdev_start_xmit(skb, dev, txq, false);

out:
        return status;
}

static void queue_process(struct work_struct *work)
{
        struct netpoll_info *npinfo =
                container_of(work, struct netpoll_info, tx_work.work);
        struct sk_buff *skb;
        unsigned long flags;

        while ((skb = skb_dequeue(&npinfo->txq))) {
                struct net_device *dev = skb->dev;
                struct netdev_queue *txq;
                unsigned int q_index;

                if (!netif_device_present(dev) || !netif_running(dev)) {
                        kfree_skb(skb);
                        continue;
                }

                local_irq_save(flags);
                /* check if skb->queue_mapping is still valid */
                q_index = skb_get_queue_mapping(skb);
                if (unlikely(q_index >= dev->real_num_tx_queues)) {
                        q_index = q_index % dev->real_num_tx_queues;
                        skb_set_queue_mapping(skb, q_index);
                }
                txq = netdev_get_tx_queue(dev, q_index);
                HARD_TX_LOCK(dev, txq, smp_processor_id());
                if (netif_xmit_frozen_or_stopped(txq) ||
                    netpoll_start_xmit(skb, dev, txq) != NETDEV_TX_OK) {
                        skb_queue_head(&npinfo->txq, skb);
                        HARD_TX_UNLOCK(dev, txq);
                        local_irq_restore(flags);

                        schedule_delayed_work(&npinfo->tx_work, HZ/10);
                        return;
                }
                HARD_TX_UNLOCK(dev, txq);
                local_irq_restore(flags);
        }
}

/*
 * Check whether delayed processing was scheduled for our NIC. If so,
 * we attempt to grab the poll lock and use ->poll() to pump the card.
 * If this fails, either we've recursed in ->poll() or it's already
 * running on another CPU.
 *
 * Note: we don't mask interrupts with this lock because we're using
 * trylock here and interrupts are already disabled in the softirq
 * case. Further, we test the poll_owner to avoid recursion on UP
 * systems where the lock doesn't exist.
 */
static void poll_one_napi(struct napi_struct *napi)
{
        int work = 0;

        /* net_rx_action's ->poll() invocations and our's are
         * synchronized by this test which is only made while
         * holding the napi->poll_lock.
         */
        if (!test_bit(NAPI_STATE_SCHED, &napi->state))
                return;

        /* If we set this bit but see that it has already been set,
         * that indicates that napi has been disabled and we need
         * to abort this operation
         */
        if (test_and_set_bit(NAPI_STATE_NPSVC, &napi->state))
                return;

        /* We explicilty pass the polling call a budget of 0 to
         * indicate that we are clearing the Tx path only.
         */
        work = napi->poll(napi, 0);
        WARN_ONCE(work, "%pF exceeded budget in poll\n", napi->poll);
        trace_napi_poll(napi, work, 0);

        clear_bit(NAPI_STATE_NPSVC, &napi->state);
}

static void poll_napi(struct net_device *dev)
{
        struct napi_struct *napi;
        int cpu = smp_processor_id();

        list_for_each_entry(napi, &dev->napi_list, dev_list) {
                if (cmpxchg(&napi->poll_owner, -1, cpu) == -1) {
                        poll_one_napi(napi);
                        smp_store_release(&napi->poll_owner, -1);
                }
        }
}

static void netpoll_poll_dev(struct net_device *dev)
{
        const struct net_device_ops *ops;
        struct netpoll_info *ni = rcu_dereference_bh(dev->npinfo);

        /* Don't do any rx activity if the dev_lock mutex is held
         * the dev_open/close paths use this to block netpoll activity
         * while changing device state
         */
        if (down_trylock(&ni->dev_lock))
                return;

        if (!netif_running(dev)) {
                up(&ni->dev_lock);
                return;
        }

        ops = dev->netdev_ops;
        if (!ops->ndo_poll_controller) {
                up(&ni->dev_lock);
                return;
        }

        /* Process pending work on NIC */
        ops->ndo_poll_controller(dev);

        poll_napi(dev);

        up(&ni->dev_lock);

        zap_completion_queue();
}

void netpoll_poll_disable(struct net_device *dev)
{
        struct netpoll_info *ni;
        int idx;
        might_sleep();
        idx = srcu_read_lock(&netpoll_srcu);
        ni = srcu_dereference(dev->npinfo, &netpoll_srcu);
        if (ni)
                down(&ni->dev_lock);
        srcu_read_unlock(&netpoll_srcu, idx);
}
EXPORT_SYMBOL(netpoll_poll_disable);

void netpoll_poll_enable(struct net_device *dev)
{
        struct netpoll_info *ni;
        rcu_read_lock();
        ni = rcu_dereference(dev->npinfo);
        if (ni)
                up(&ni->dev_lock);
        rcu_read_unlock();
}
EXPORT_SYMBOL(netpoll_poll_enable);

static void refill_skbs(void)
{
        struct sk_buff *skb;
        unsigned long flags;

        spin_lock_irqsave(&skb_pool.lock, flags);
        while (skb_pool.qlen < MAX_SKBS) {
                skb = alloc_skb(MAX_SKB_SIZE, GFP_ATOMIC);
                if (!skb)
                        break;

                __skb_queue_tail(&skb_pool, skb);
        }
        spin_unlock_irqrestore(&skb_pool.lock, flags);
}

static void zap_completion_queue(void)
{
        unsigned long flags;
        struct softnet_data *sd = &get_cpu_var(softnet_data);

        if (sd->completion_queue) {
                struct sk_buff *clist;

                local_irq_save(flags);
                clist = sd->completion_queue;
                sd->completion_queue = NULL;
                local_irq_restore(flags);

                while (clist != NULL) {
                        struct sk_buff *skb = clist;
                        clist = clist->next;
                        if (!skb_irq_freeable(skb)) {
                                refcount_set(&skb->users, 1);
                                dev_kfree_skb_any(skb); /* put this one back */
                        } else {
                                __kfree_skb(skb);
                        }
                }
        }

        put_cpu_var(softnet_data);
}

static struct sk_buff *find_skb(struct netpoll *np, int len, int reserve)
{
        int count = 0;
        struct sk_buff *skb;

        zap_completion_queue();
        refill_skbs();
repeat:

        skb = alloc_skb(len, GFP_ATOMIC);
        if (!skb)
                skb = skb_dequeue(&skb_pool);

        if (!skb) {
                if (++count < 10) {
                        netpoll_poll_dev(np->dev);
                        goto repeat;
                }
                return NULL;
        }

        refcount_set(&skb->users, 1);
        skb_reserve(skb, reserve);
        return skb;
}

static int netpoll_owner_active(struct net_device *dev)
{
        struct napi_struct *napi;

        list_for_each_entry(napi, &dev->napi_list, dev_list) {
                if (napi->poll_owner == smp_processor_id())
                        return 1;
        }
        return 0;
}

/* call with IRQ disabled */
void netpoll_send_skb_on_dev(struct netpoll *np, struct sk_buff *skb,
                             struct net_device *dev)
{
        int status = NETDEV_TX_BUSY;
        unsigned long tries;
        /* It is up to the caller to keep npinfo alive. */
        struct netpoll_info *npinfo;

        WARN_ON_ONCE(!irqs_disabled());

        npinfo = rcu_dereference_bh(np->dev->npinfo);
        if (!npinfo || !netif_running(dev) || !netif_device_present(dev)) {
                dev_kfree_skb_irq(skb);
                return;
        }

        /* don't get messages out of order, and no recursion */
        if (skb_queue_len(&npinfo->txq) == 0 && !netpoll_owner_active(dev)) {
                struct netdev_queue *txq;

                txq = netdev_pick_tx(dev, skb, NULL);

                /* try until next clock tick */
                for (tries = jiffies_to_usecs(1)/USEC_PER_POLL;
                     tries > 0; --tries) {
                        if (HARD_TX_TRYLOCK(dev, txq)) {
                                if (!netif_xmit_stopped(txq))
                                        status = netpoll_start_xmit(skb, dev, txq);

                                HARD_TX_UNLOCK(dev, txq);

                                if (status == NETDEV_TX_OK)
                                        break;

                        }

                        /* tickle device maybe there is some cleanup */
                        netpoll_poll_dev(np->dev);

                        udelay(USEC_PER_POLL);
                }

                WARN_ONCE(!irqs_disabled(),
                        "netpoll_send_skb_on_dev(): %s enabled interrupts in poll (%pF)\n",
                        dev->name, dev->netdev_ops->ndo_start_xmit);

        }

        if (status != NETDEV_TX_OK) {
                skb_queue_tail(&npinfo->txq, skb);
                schedule_delayed_work(&npinfo->tx_work,0);
        }
}
EXPORT_SYMBOL(netpoll_send_skb_on_dev);

void netpoll_send_udp(struct netpoll *np, const char *msg, int len)
{
        int total_len, ip_len, udp_len;
        struct sk_buff *skb;
        struct udphdr *udph;
        struct iphdr *iph;
        struct ethhdr *eth;
        static atomic_t ip_ident;
        struct ipv6hdr *ip6h;

        WARN_ON_ONCE(!irqs_disabled());

        udp_len = len + sizeof(*udph);
        if (np->ipv6)
                ip_len = udp_len + sizeof(*ip6h);
        else
                ip_len = udp_len + sizeof(*iph);

        total_len = ip_len + LL_RESERVED_SPACE(np->dev);

        skb = find_skb(np, total_len + np->dev->needed_tailroom,
                       total_len - len);
        if (!skb)
                return;

        skb_copy_to_linear_data(skb, msg, len);
        skb_put(skb, len);

        skb_push(skb, sizeof(*udph));
        skb_reset_transport_header(skb);
        udph = udp_hdr(skb);
        udph->source = htons(np->local_port);
        udph->dest = htons(np->remote_port);
        udph->len = htons(udp_len);

        if (np->ipv6) {
                udph->check = 0;
                udph->check = csum_ipv6_magic(&np->local_ip.in6,
                                              &np->remote_ip.in6,
                                              udp_len, IPPROTO_UDP,
                                              csum_partial(udph, udp_len, 0));
                if (udph->check == 0)
                        udph->check = CSUM_MANGLED_0;

                skb_push(skb, sizeof(*ip6h));
                skb_reset_network_header(skb);
                ip6h = ipv6_hdr(skb);

                /* ip6h->version = 6; ip6h->priority = 0; */
                put_unaligned(0x60, (unsigned char *)ip6h);
                ip6h->flow_lbl[0] = 0;
                ip6h->flow_lbl[1] = 0;
                ip6h->flow_lbl[2] = 0;

                ip6h->payload_len = htons(sizeof(struct udphdr) + len);
                ip6h->nexthdr = IPPROTO_UDP;
                ip6h->hop_limit = 32;
                ip6h->saddr = np->local_ip.in6;
                ip6h->daddr = np->remote_ip.in6;

                eth = skb_push(skb, ETH_HLEN);
                skb_reset_mac_header(skb);
                skb->protocol = eth->h_proto = htons(ETH_P_IPV6);
        } else {
                udph->check = 0;
                udph->check = csum_tcpudp_magic(np->local_ip.ip,
                                                np->remote_ip.ip,
                                                udp_len, IPPROTO_UDP,
                                                csum_partial(udph, udp_len, 0));
                if (udph->check == 0)
                        udph->check = CSUM_MANGLED_0;

                skb_push(skb, sizeof(*iph));
                skb_reset_network_header(skb);
                iph = ip_hdr(skb);

                /* iph->version = 4; iph->ihl = 5; */
                put_unaligned(0x45, (unsigned char *)iph);
                iph->tos      = 0;
                put_unaligned(htons(ip_len), &(iph->tot_len));
                iph->id       = htons(atomic_inc_return(&ip_ident));
                iph->frag_off = 0;
                iph->ttl      = 64;
                iph->protocol = IPPROTO_UDP;
                iph->check    = 0;
                put_unaligned(np->local_ip.ip, &(iph->saddr));
                put_unaligned(np->remote_ip.ip, &(iph->daddr));
                iph->check    = ip_fast_csum((unsigned char *)iph, iph->ihl);

                eth = skb_push(skb, ETH_HLEN);
                skb_reset_mac_header(skb);
                skb->protocol = eth->h_proto = htons(ETH_P_IP);
        }

        ether_addr_copy(eth->h_source, np->dev->dev_addr);
        ether_addr_copy(eth->h_dest, np->remote_mac);

        skb->dev = np->dev;

        netpoll_send_skb(np, skb);
}
EXPORT_SYMBOL(netpoll_send_udp);

void netpoll_print_options(struct netpoll *np)
{
        np_info(np, "local port %d\n", np->local_port);
        if (np->ipv6)
                np_info(np, "local IPv6 address %pI6c\n", &np->local_ip.in6);
        else
                np_info(np, "local IPv4 address %pI4\n", &np->local_ip.ip);
        np_info(np, "interface '%s'\n", np->dev_name);
        np_info(np, "remote port %d\n", np->remote_port);
        if (np->ipv6)
                np_info(np, "remote IPv6 address %pI6c\n", &np->remote_ip.in6);
        else
                np_info(np, "remote IPv4 address %pI4\n", &np->remote_ip.ip);
        np_info(np, "remote ethernet address %pM\n", np->remote_mac);
}
EXPORT_SYMBOL(netpoll_print_options);

static int netpoll_parse_ip_addr(const char *str, union inet_addr *addr)
{
        const char *end;

        if (!strchr(str, ':') &&
            in4_pton(str, -1, (void *)addr, -1, &end) > 0) {
                if (!*end)
                        return 0;
        }
        if (in6_pton(str, -1, addr->in6.s6_addr, -1, &end) > 0) {
#if IS_ENABLED(CONFIG_IPV6)
                if (!*end)
                        return 1;
#else
                return -1;
#endif
        }
        return -1;
}

int netpoll_parse_options(struct netpoll *np, char *opt)
{
        char *cur=opt, *delim;
        int ipv6;
        bool ipversion_set = false;

        if (*cur != '@') {
                if ((delim = strchr(cur, '@')) == NULL)
                        goto parse_failed;
                *delim = 0;
                if (kstrtou16(cur, 10, &np->local_port))
                        goto parse_failed;
                cur = delim;
        }
        cur++;

        if (*cur != '/') {
                ipversion_set = true;
                if ((delim = strchr(cur, '/')) == NULL)
                        goto parse_failed;
                *delim = 0;
                ipv6 = netpoll_parse_ip_addr(cur, &np->local_ip);
                if (ipv6 < 0)
                        goto parse_failed;
                else
                        np->ipv6 = (bool)ipv6;
                cur = delim;
        }
        cur++;

        if (*cur != ',') {
                /* parse out dev name */
                if ((delim = strchr(cur, ',')) == NULL)
                        goto parse_failed;
                *delim = 0;
                strlcpy(np->dev_name, cur, sizeof(np->dev_name));
                cur = delim;
        }
        cur++;

        if (*cur != '@') {
                /* dst port */
                if ((delim = strchr(cur, '@')) == NULL)
                        goto parse_failed;
                *delim = 0;
                if (*cur == ' ' || *cur == '\t')
                        np_info(np, "warning: whitespace is not allowed\n");
                if (kstrtou16(cur, 10, &np->remote_port))
                        goto parse_failed;
                cur = delim;
        }
        cur++;

        /* dst ip */
        if ((delim = strchr(cur, '/')) == NULL)
                goto parse_failed;
        *delim = 0;
        ipv6 = netpoll_parse_ip_addr(cur, &np->remote_ip);
        if (ipv6 < 0)
                goto parse_failed;
        else if (ipversion_set && np->ipv6 != (bool)ipv6)
                goto parse_failed;
        else
                np->ipv6 = (bool)ipv6;
        cur = delim + 1;

        if (*cur != 0) {
                /* MAC address */
                if (!mac_pton(cur, np->remote_mac))
                        goto parse_failed;
        }

        netpoll_print_options(np);

        return 0;

 parse_failed:
        np_info(np, "couldn't parse config at '%s'!\n", cur);
        return -1;
}
EXPORT_SYMBOL(netpoll_parse_options);

int __netpoll_setup(struct netpoll *np, struct net_device *ndev)
{
        struct netpoll_info *npinfo;
        const struct net_device_ops *ops;
        int err;

        np->dev = ndev;
        strlcpy(np->dev_name, ndev->name, IFNAMSIZ);
        INIT_WORK(&np->cleanup_work, netpoll_async_cleanup);

        if ((ndev->priv_flags & IFF_DISABLE_NETPOLL) ||
            !ndev->netdev_ops->ndo_poll_controller) {
                np_err(np, "%s doesn't support polling, aborting\n",
                       np->dev_name);
                err = -ENOTSUPP;
                goto out;
        }

        if (!ndev->npinfo) {
                npinfo = kmalloc(sizeof(*npinfo), GFP_KERNEL);
                if (!npinfo) {
                        err = -ENOMEM;
                        goto out;
                }

                sema_init(&npinfo->dev_lock, 1);
                skb_queue_head_init(&npinfo->txq);
                INIT_DELAYED_WORK(&npinfo->tx_work, queue_process);

                refcount_set(&npinfo->refcnt, 1);

                ops = np->dev->netdev_ops;
                if (ops->ndo_netpoll_setup) {
                        err = ops->ndo_netpoll_setup(ndev, npinfo);
                        if (err)
                                goto free_npinfo;
                }
        } else {
                npinfo = rtnl_dereference(ndev->npinfo);
                refcount_inc(&npinfo->refcnt);
        }

        npinfo->netpoll = np;

        /* last thing to do is link it to the net device structure */
        rcu_assign_pointer(ndev->npinfo, npinfo);

        return 0;

free_npinfo:
        kfree(npinfo);
out:
        return err;
}
EXPORT_SYMBOL_GPL(__netpoll_setup);

int netpoll_setup(struct netpoll *np)
{
        struct net_device *ndev = NULL;
        struct in_device *in_dev;
        int err;

        rtnl_lock();
        if (np->dev_name[0]) {
                struct net *net = current->nsproxy->net_ns;
                ndev = __dev_get_by_name(net, np->dev_name);
        }
        if (!ndev) {
                np_err(np, "%s doesn't exist, aborting\n", np->dev_name);
                err = -ENODEV;
                goto unlock;
        }
        dev_hold(ndev);

        if (netdev_master_upper_dev_get(ndev)) {
                np_err(np, "%s is a slave device, aborting\n", np->dev_name);
                err = -EBUSY;
                goto put;
        }

        if (!netif_running(ndev)) {
                unsigned long atmost, atleast;

                np_info(np, "device %s not up yet, forcing it\n", np->dev_name);

                err = dev_open(ndev);

                if (err) {
                        np_err(np, "failed to open %s\n", ndev->name);
                        goto put;
                }

                rtnl_unlock();
                atleast = jiffies + HZ/10;
                atmost = jiffies + carrier_timeout * HZ;
                while (!netif_carrier_ok(ndev)) {
                        if (time_after(jiffies, atmost)) {
                                np_notice(np, "timeout waiting for carrier\n");
                                break;
                        }
                        msleep(1);
                }

                /* If carrier appears to come up instantly, we don't
                 * trust it and pause so that we don't pump all our
                 * queued console messages into the bitbucket.
                 */

                if (time_before(jiffies, atleast)) {
                        np_notice(np, "carrier detect appears untrustworthy, waiting 4 seconds\n");
                        msleep(4000);
                }
                rtnl_lock();
        }

        if (!np->local_ip.ip) {
                if (!np->ipv6) {
                        in_dev = __in_dev_get_rtnl(ndev);

                        if (!in_dev || !in_dev->ifa_list) {
                                np_err(np, "no IP address for %s, aborting\n",
                                       np->dev_name);
                                err = -EDESTADDRREQ;
                                goto put;
                        }

                        np->local_ip.ip = in_dev->ifa_list->ifa_local;
                        np_info(np, "local IP %pI4\n", &np->local_ip.ip);
                } else {
#if IS_ENABLED(CONFIG_IPV6)
                        struct inet6_dev *idev;

                        err = -EDESTADDRREQ;
                        idev = __in6_dev_get(ndev);
                        if (idev) {
                                struct inet6_ifaddr *ifp;

                                read_lock_bh(&idev->lock);
                                list_for_each_entry(ifp, &idev->addr_list, if_list) {
                                        if (ipv6_addr_type(&ifp->addr) & IPV6_ADDR_LINKLOCAL)
                                                continue;
                                        np->local_ip.in6 = ifp->addr;
                                        err = 0;
                                        break;
                                }
                                read_unlock_bh(&idev->lock);
                        }
                        if (err) {
                                np_err(np, "no IPv6 address for %s, aborting\n",
                                       np->dev_name);
                                goto put;
                        } else
                                np_info(np, "local IPv6 %pI6c\n", &np->local_ip.in6);
#else
                        np_err(np, "IPv6 is not supported %s, aborting\n",
                               np->dev_name);
                        err = -EINVAL;
                        goto put;
#endif
                }
        }

        /* fill up the skb queue */
        refill_skbs();

        err = __netpoll_setup(np, ndev);
        if (err)
                goto put;

        rtnl_unlock();
        return 0;

put:
        dev_put(ndev);
unlock:
        rtnl_unlock();
        return err;
}
EXPORT_SYMBOL(netpoll_setup);

static int __init netpoll_init(void)
{
        skb_queue_head_init(&skb_pool);
        return 0;
}
core_initcall(netpoll_init);

static void rcu_cleanup_netpoll_info(struct rcu_head *rcu_head)
{
        struct netpoll_info *npinfo =
                        container_of(rcu_head, struct netpoll_info, rcu);

        skb_queue_purge(&npinfo->txq);

        /* we can't call cancel_delayed_work_sync here, as we are in softirq */
        cancel_delayed_work(&npinfo->tx_work);

        /* clean after last, unfinished work */
        __skb_queue_purge(&npinfo->txq);
        /* now cancel it again */
        cancel_delayed_work(&npinfo->tx_work);
        kfree(npinfo);
}

void __netpoll_cleanup(struct netpoll *np)
{
        struct netpoll_info *npinfo;

        /* rtnl_dereference would be preferable here but
         * rcu_cleanup_netpoll path can put us in here safely without
         * holding the rtnl, so plain rcu_dereference it is
         */
        npinfo = rtnl_dereference(np->dev->npinfo);
        if (!npinfo)
                return;

        synchronize_srcu(&netpoll_srcu);

        if (refcount_dec_and_test(&npinfo->refcnt)) {
                const struct net_device_ops *ops;

                ops = np->dev->netdev_ops;
                if (ops->ndo_netpoll_cleanup)
                        ops->ndo_netpoll_cleanup(np->dev);

                RCU_INIT_POINTER(np->dev->npinfo, NULL);
                call_rcu_bh(&npinfo->rcu, rcu_cleanup_netpoll_info);
        } else
                RCU_INIT_POINTER(np->dev->npinfo, NULL);
}
EXPORT_SYMBOL_GPL(__netpoll_cleanup);

static void netpoll_async_cleanup(struct work_struct *work)
{
        struct netpoll *np = container_of(work, struct netpoll, cleanup_work);

        rtnl_lock();
        __netpoll_cleanup(np);
        rtnl_unlock();
        kfree(np);
}

void __netpoll_free_async(struct netpoll *np)
{
        schedule_work(&np->cleanup_work);
}
EXPORT_SYMBOL_GPL(__netpoll_free_async);

void netpoll_cleanup(struct netpoll *np)
{
        rtnl_lock();
        if (!np->dev)
                goto out;
        __netpoll_cleanup(np);
        dev_put(np->dev);
        np->dev = NULL;
out:
        rtnl_unlock();
}
EXPORT_SYMBOL(netpoll_cleanup);