Merge branch 'ipmr-remove-rwlocks'

Eric Dumazet says:

====================
ipmr: get rid of rwlocks

We need to get rid of rwlocks in networking stacks,
if read_lock() is (ab)used from softirq context.

As discussed recently [1], rwlock are unfair by design in this case,
and writers can starve and trigger soft lockups.

This series convert ipmr code (both IPv4 and IPv6 families)
to RCU and spinlocks.

[1] https://lkml.org/lkml/2022/6/17/272

v2: fixed two typos, and resent because patch 19/19
    did not make it to patchwork.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

4 files changed, 255 insertions, 230 deletions

diff --git a/include/linux/mroute_base.h b/include/linux/mroute_base.h
index e05ee9f001ff..9dd4bf157255 100644
--- a/include/linux/mroute_base.h
+++ b/include/linux/mroute_base.h
@@ -26,7 +26,7 @@
  * @remote: Remote address for tunnels
  */
 struct vif_device {
-	struct net_device *dev;
+	struct net_device __rcu *dev;
 	netdevice_tracker dev_tracker;
 	unsigned long bytes_in, bytes_out;
 	unsigned long pkt_in, pkt_out;
@@ -52,6 +52,7 @@ static inline int mr_call_vif_notifier(struct notifier_block *nb,
 				       unsigned short family,
 				       enum fib_event_type event_type,
 				       struct vif_device *vif,
+				       struct net_device *vif_dev,
 				       unsigned short vif_index, u32 tb_id,
 				       struct netlink_ext_ack *extack)
 {
@@ -60,7 +61,7 @@ static inline int mr_call_vif_notifier(struct notifier_block *nb,
 			.family = family,
 			.extack = extack,
 		},
-		.dev = vif->dev,
+		.dev = vif_dev,
 		.vif_index = vif_index,
 		.vif_flags = vif->flags,
 		.tb_id = tb_id,
@@ -73,6 +74,7 @@ static inline int mr_call_vif_notifiers(struct net *net,
 					unsigned short family,
 					enum fib_event_type event_type,
 					struct vif_device *vif,
+					struct net_device *vif_dev,
 					unsigned short vif_index, u32 tb_id,
 					unsigned int *ipmr_seq)
 {
@@ -80,7 +82,7 @@ static inline int mr_call_vif_notifiers(struct net *net,
 		.info = {
 			.family = family,
 		},
-		.dev = vif->dev,
+		.dev = vif_dev,
 		.vif_index = vif_index,
 		.vif_flags = vif->flags,
 		.tb_id = tb_id,
@@ -98,7 +100,8 @@ static inline int mr_call_vif_notifiers(struct net *net,
 #define MAXVIFS	32
 #endif
 
-#define VIF_EXISTS(_mrt, _idx) (!!((_mrt)->vif_table[_idx].dev))
+/* Note: This helper is deprecated. */
+#define VIF_EXISTS(_mrt, _idx) (!!rcu_access_pointer((_mrt)->vif_table[_idx].dev))
 
 /* mfc_flags:
  * MFC_STATIC - the entry was added statically (not by a routing daemon)
@@ -305,7 +308,7 @@ int mr_dump(struct net *net, struct notifier_block *nb, unsigned short family,
 			      struct netlink_ext_ack *extack),
 	    struct mr_table *(*mr_iter)(struct net *net,
 					struct mr_table *mrt),
-	    rwlock_t *mrt_lock, struct netlink_ext_ack *extack);
+	    struct netlink_ext_ack *extack);
 #else
 static inline void vif_device_init(struct vif_device *v,
 				   struct net_device *dev,
@@ -360,7 +363,7 @@ static inline int mr_dump(struct net *net, struct notifier_block *nb,
 					    struct netlink_ext_ack *extack),
 			  struct mr_table *(*mr_iter)(struct net *net,
 						      struct mr_table *mrt),
-			  rwlock_t *mrt_lock, struct netlink_ext_ack *extack)
+			  struct netlink_ext_ack *extack)
 {
 	return -EINVAL;
 }
diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index 8324e541d193..f095b6c8100b 100644
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -77,7 +77,12 @@ struct ipmr_result {
  * Note that the changes are semaphored via rtnl_lock.
  */
 
-static DEFINE_RWLOCK(mrt_lock);
+static DEFINE_SPINLOCK(mrt_lock);
+
+static struct net_device *vif_dev_read(const struct vif_device *vif)
+{
+	return rcu_dereference(vif->dev);
+}
 
 /* Multicast router control variables */
 
@@ -100,11 +105,11 @@ static void ipmr_free_table(struct mr_table *mrt);
 static void ip_mr_forward(struct net *net, struct mr_table *mrt,
 			  struct net_device *dev, struct sk_buff *skb,
 			  struct mfc_cache *cache, int local);
-static int ipmr_cache_report(struct mr_table *mrt,
+static int ipmr_cache_report(const struct mr_table *mrt,
 			     struct sk_buff *pkt, vifi_t vifi, int assert);
 static void mroute_netlink_event(struct mr_table *mrt, struct mfc_cache *mfc,
 				 int cmd);
-static void igmpmsg_netlink_event(struct mr_table *mrt, struct sk_buff *pkt);
+static void igmpmsg_netlink_event(const struct mr_table *mrt, struct sk_buff *pkt);
 static void mroute_clean_tables(struct mr_table *mrt, int flags);
 static void ipmr_expire_process(struct timer_list *t);
 
@@ -501,11 +506,15 @@ static netdev_tx_t reg_vif_xmit(struct sk_buff *skb, struct net_device *dev)
 		return err;
 	}
 
-	read_lock(&mrt_lock);
 	dev->stats.tx_bytes += skb->len;
 	dev->stats.tx_packets++;
-	ipmr_cache_report(mrt, skb, mrt->mroute_reg_vif_num, IGMPMSG_WHOLEPKT);
-	read_unlock(&mrt_lock);
+	rcu_read_lock();
+
+	/* Pairs with WRITE_ONCE() in vif_add() and vif_delete() */
+	ipmr_cache_report(mrt, skb, READ_ONCE(mrt->mroute_reg_vif_num),
+			  IGMPMSG_WHOLEPKT);
+
+	rcu_read_unlock();
 	kfree_skb(skb);
 	return NETDEV_TX_OK;
 }
@@ -572,6 +581,7 @@ static int __pim_rcv(struct mr_table *mrt, struct sk_buff *skb,
 {
 	struct net_device *reg_dev = NULL;
 	struct iphdr *encap;
+	int vif_num;
 
 	encap = (struct iphdr *)(skb_transport_header(skb) + pimlen);
 	/* Check that:
@@ -584,11 +594,10 @@ static int __pim_rcv(struct mr_table *mrt, struct sk_buff *skb,
 	    ntohs(encap->tot_len) + pimlen > skb->len)
 		return 1;
 
-	read_lock(&mrt_lock);
-	if (mrt->mroute_reg_vif_num >= 0)
-		reg_dev = mrt->vif_table[mrt->mroute_reg_vif_num].dev;
-	read_unlock(&mrt_lock);
-
+	/* Pairs with WRITE_ONCE() in vif_add()/vid_delete() */
+	vif_num = READ_ONCE(mrt->mroute_reg_vif_num);
+	if (vif_num >= 0)
+		reg_dev = vif_dev_read(&mrt->vif_table[vif_num]);
 	if (!reg_dev)
 		return 1;
 
@@ -614,10 +623,11 @@ static struct net_device *ipmr_reg_vif(struct net *net, struct mr_table *mrt)
 static int call_ipmr_vif_entry_notifiers(struct net *net,
 					 enum fib_event_type event_type,
 					 struct vif_device *vif,
+					 struct net_device *vif_dev,
 					 vifi_t vif_index, u32 tb_id)
 {
 	return mr_call_vif_notifiers(net, RTNL_FAMILY_IPMR, event_type,
-				     vif, vif_index, tb_id,
+				     vif, vif_dev, vif_index, tb_id,
 				     &net->ipv4.ipmr_seq);
 }
 
@@ -649,22 +659,19 @@ static int vif_delete(struct mr_table *mrt, int vifi, int notify,
 
 	v = &mrt->vif_table[vifi];
 
-	if (VIF_EXISTS(mrt, vifi))
-		call_ipmr_vif_entry_notifiers(net, FIB_EVENT_VIF_DEL, v, vifi,
-					      mrt->id);
-
-	write_lock_bh(&mrt_lock);
-	dev = v->dev;
-	v->dev = NULL;
-
-	if (!dev) {
-		write_unlock_bh(&mrt_lock);
+	dev = rtnl_dereference(v->dev);
+	if (!dev)
 		return -EADDRNOTAVAIL;
-	}
 
-	if (vifi == mrt->mroute_reg_vif_num)
-		mrt->mroute_reg_vif_num = -1;
+	spin_lock(&mrt_lock);
+	call_ipmr_vif_entry_notifiers(net, FIB_EVENT_VIF_DEL, v, dev,
+				      vifi, mrt->id);
+	RCU_INIT_POINTER(v->dev, NULL);
 
+	if (vifi == mrt->mroute_reg_vif_num) {
+		/* Pairs with READ_ONCE() in ipmr_cache_report() and reg_vif_xmit() */
+		WRITE_ONCE(mrt->mroute_reg_vif_num, -1);
+	}
 	if (vifi + 1 == mrt->maxvif) {
 		int tmp;
 
@@ -672,10 +679,10 @@ static int vif_delete(struct mr_table *mrt, int vifi, int notify,
 			if (VIF_EXISTS(mrt, tmp))
 				break;
 		}
-		mrt->maxvif = tmp+1;
+		WRITE_ONCE(mrt->maxvif, tmp + 1);
 	}
 
-	write_unlock_bh(&mrt_lock);
+	spin_unlock(&mrt_lock);
 
 	dev_set_allmulti(dev, -1);
 
@@ -777,7 +784,7 @@ out:
 	spin_unlock(&mfc_unres_lock);
 }
 
-/* Fill oifs list. It is called under write locked mrt_lock. */
+/* Fill oifs list. It is called under locked mrt_lock. */
 static void ipmr_update_thresholds(struct mr_table *mrt, struct mr_mfc *cache,
 				   unsigned char *ttls)
 {
@@ -889,15 +896,18 @@ static int vif_add(struct net *net, struct mr_table *mrt,
 	v->remote = vifc->vifc_rmt_addr.s_addr;
 
 	/* And finish update writing critical data */
-	write_lock_bh(&mrt_lock);
-	v->dev = dev;
+	spin_lock(&mrt_lock);
+	rcu_assign_pointer(v->dev, dev);
 	netdev_tracker_alloc(dev, &v->dev_tracker, GFP_ATOMIC);
-	if (v->flags & VIFF_REGISTER)
-		mrt->mroute_reg_vif_num = vifi;
+	if (v->flags & VIFF_REGISTER) {
+		/* Pairs with READ_ONCE() in ipmr_cache_report() and reg_vif_xmit() */
+		WRITE_ONCE(mrt->mroute_reg_vif_num, vifi);
+	}
 	if (vifi+1 > mrt->maxvif)
-		mrt->maxvif = vifi+1;
-	write_unlock_bh(&mrt_lock);
-	call_ipmr_vif_entry_notifiers(net, FIB_EVENT_VIF_ADD, v, vifi, mrt->id);
+		WRITE_ONCE(mrt->maxvif, vifi + 1);
+	spin_unlock(&mrt_lock);
+	call_ipmr_vif_entry_notifiers(net, FIB_EVENT_VIF_ADD, v, dev,
+				      vifi, mrt->id);
 	return 0;
 }
 
@@ -1001,9 +1011,9 @@ static void ipmr_cache_resolve(struct net *net, struct mr_table *mrt,
 
 /* Bounce a cache query up to mrouted and netlink.
  *
- * Called under mrt_lock.
+ * Called under rcu_read_lock().
  */
-static int ipmr_cache_report(struct mr_table *mrt,
+static int ipmr_cache_report(const struct mr_table *mrt,
 			     struct sk_buff *pkt, vifi_t vifi, int assert)
 {
 	const int ihl = ip_hdrlen(pkt);
@@ -1038,8 +1048,11 @@ static int ipmr_cache_report(struct mr_table *mrt,
 			msg->im_vif = vifi;
 			msg->im_vif_hi = vifi >> 8;
 		} else {
-			msg->im_vif = mrt->mroute_reg_vif_num;
-			msg->im_vif_hi = mrt->mroute_reg_vif_num >> 8;
+			/* Pairs with WRITE_ONCE() in vif_add() and vif_delete() */
+			int vif_num = READ_ONCE(mrt->mroute_reg_vif_num);
+
+			msg->im_vif = vif_num;
+			msg->im_vif_hi = vif_num >> 8;
 		}
 		ip_hdr(skb)->ihl = sizeof(struct iphdr) >> 2;
 		ip_hdr(skb)->tot_len = htons(ntohs(ip_hdr(pkt)->tot_len) +
@@ -1064,10 +1077,8 @@ static int ipmr_cache_report(struct mr_table *mrt,
 		skb->transport_header = skb->network_header;
 	}
 
-	rcu_read_lock();
 	mroute_sk = rcu_dereference(mrt->mroute_sk);
 	if (!mroute_sk) {
-		rcu_read_unlock();
 		kfree_skb(skb);
 		return -EINVAL;
 	}
@@ -1076,7 +1087,7 @@ static int ipmr_cache_report(struct mr_table *mrt,
 
 	/* Deliver to mrouted */
 	ret = sock_queue_rcv_skb(mroute_sk, skb);
-	rcu_read_unlock();
+
 	if (ret < 0) {
 		net_warn_ratelimited("mroute: pending queue full, dropping entries\n");
 		kfree_skb(skb);
@@ -1086,6 +1097,7 @@ static int ipmr_cache_report(struct mr_table *mrt,
 }
 
 /* Queue a packet for resolution. It gets locked cache entry! */
+/* Called under rcu_read_lock() */
 static int ipmr_cache_unresolved(struct mr_table *mrt, vifi_t vifi,
 				 struct sk_buff *skb, struct net_device *dev)
 {
@@ -1198,12 +1210,12 @@ static int ipmr_mfc_add(struct net *net, struct mr_table *mrt,
 				   mfc->mfcc_mcastgrp.s_addr, parent);
 	rcu_read_unlock();
 	if (c) {
-		write_lock_bh(&mrt_lock);
+		spin_lock(&mrt_lock);
 		c->_c.mfc_parent = mfc->mfcc_parent;
 		ipmr_update_thresholds(mrt, &c->_c, mfc->mfcc_ttls);
 		if (!mrtsock)
 			c->_c.mfc_flags |= MFC_STATIC;
-		write_unlock_bh(&mrt_lock);
+		spin_unlock(&mrt_lock);
 		call_ipmr_mfc_entry_notifiers(net, FIB_EVENT_ENTRY_REPLACE, c,
 					      mrt->id);
 		mroute_netlink_event(mrt, c, RTM_NEWROUTE);
@@ -1598,20 +1610,20 @@ int ipmr_ioctl(struct sock *sk, int cmd, void __user *arg)
 		if (vr.vifi >= mrt->maxvif)
 			return -EINVAL;
 		vr.vifi = array_index_nospec(vr.vifi, mrt->maxvif);
-		read_lock(&mrt_lock);
+		rcu_read_lock();
 		vif = &mrt->vif_table[vr.vifi];
 		if (VIF_EXISTS(mrt, vr.vifi)) {
-			vr.icount = vif->pkt_in;
-			vr.ocount = vif->pkt_out;
-			vr.ibytes = vif->bytes_in;
-			vr.obytes = vif->bytes_out;
-			read_unlock(&mrt_lock);
+			vr.icount = READ_ONCE(vif->pkt_in);
+			vr.ocount = READ_ONCE(vif->pkt_out);
+			vr.ibytes = READ_ONCE(vif->bytes_in);
+			vr.obytes = READ_ONCE(vif->bytes_out);
+			rcu_read_unlock();
 
 			if (copy_to_user(arg, &vr, sizeof(vr)))
 				return -EFAULT;
 			return 0;
 		}
-		read_unlock(&mrt_lock);
+		rcu_read_unlock();
 		return -EADDRNOTAVAIL;
 	case SIOCGETSGCNT:
 		if (copy_from_user(&sr, arg, sizeof(sr)))
@@ -1673,20 +1685,20 @@ int ipmr_compat_ioctl(struct sock *sk, unsigned int cmd, void __user *arg)
 		if (vr.vifi >= mrt->maxvif)
 			return -EINVAL;
 		vr.vifi = array_index_nospec(vr.vifi, mrt->maxvif);
-		read_lock(&mrt_lock);
+		rcu_read_lock();
 		vif = &mrt->vif_table[vr.vifi];
 		if (VIF_EXISTS(mrt, vr.vifi)) {
-			vr.icount = vif->pkt_in;
-			vr.ocount = vif->pkt_out;
-			vr.ibytes = vif->bytes_in;
-			vr.obytes = vif->bytes_out;
-			read_unlock(&mrt_lock);
+			vr.icount = READ_ONCE(vif->pkt_in);
+			vr.ocount = READ_ONCE(vif->pkt_out);
+			vr.ibytes = READ_ONCE(vif->bytes_in);
+			vr.obytes = READ_ONCE(vif->bytes_out);
+			rcu_read_unlock();
 
 			if (copy_to_user(arg, &vr, sizeof(vr)))
 				return -EFAULT;
 			return 0;
 		}
-		read_unlock(&mrt_lock);
+		rcu_read_unlock();
 		return -EADDRNOTAVAIL;
 	case SIOCGETSGCNT:
 		if (copy_from_user(&sr, arg, sizeof(sr)))
@@ -1726,7 +1738,7 @@ static int ipmr_device_event(struct notifier_block *this, unsigned long event, v
 	ipmr_for_each_table(mrt, net) {
 		v = &mrt->vif_table[0];
 		for (ct = 0; ct < mrt->maxvif; ct++, v++) {
-			if (v->dev == dev)
+			if (rcu_access_pointer(v->dev) == dev)
 				vif_delete(mrt, ct, 1, NULL);
 		}
 	}
@@ -1804,26 +1816,28 @@ static bool ipmr_forward_offloaded(struct sk_buff *skb, struct mr_table *mrt,
 }
 #endif
 
-/* Processing handlers for ipmr_forward */
+/* Processing handlers for ipmr_forward, under rcu_read_lock() */
 
 static void ipmr_queue_xmit(struct net *net, struct mr_table *mrt,
 			    int in_vifi, struct sk_buff *skb, int vifi)
 {
 	const struct iphdr *iph = ip_hdr(skb);
 	struct vif_device *vif = &mrt->vif_table[vifi];
+	struct net_device *vif_dev;
 	struct net_device *dev;
 	struct rtable *rt;
 	struct flowi4 fl4;
 	int    encap = 0;
 
-	if (!vif->dev)
+	vif_dev = vif_dev_read(vif);
+	if (!vif_dev)
 		goto out_free;
 
 	if (vif->flags & VIFF_REGISTER) {
-		vif->pkt_out++;
-		vif->bytes_out += skb->len;
-		vif->dev->stats.tx_bytes += skb->len;
-		vif->dev->stats.tx_packets++;
+		WRITE_ONCE(vif->pkt_out, vif->pkt_out + 1);
+		WRITE_ONCE(vif->bytes_out, vif->bytes_out + skb->len);
+		vif_dev->stats.tx_bytes += skb->len;
+		vif_dev->stats.tx_packets++;
 		ipmr_cache_report(mrt, skb, vifi, IGMPMSG_WHOLEPKT);
 		goto out_free;
 	}
@@ -1868,8 +1882,8 @@ static void ipmr_queue_xmit(struct net *net, struct mr_table *mrt,
 		goto out_free;
 	}
 
-	vif->pkt_out++;
-	vif->bytes_out += skb->len;
+	WRITE_ONCE(vif->pkt_out, vif->pkt_out + 1);
+	WRITE_ONCE(vif->bytes_out, vif->bytes_out + skb->len);
 
 	skb_dst_drop(skb);
 	skb_dst_set(skb, &rt->dst);
@@ -1881,8 +1895,8 @@ static void ipmr_queue_xmit(struct net *net, struct mr_table *mrt,
 	if (vif->flags & VIFF_TUNNEL) {
 		ip_encap(net, skb, vif->local, vif->remote);
 		/* FIXME: extra output firewall step used to be here. --RR */
-		vif->dev->stats.tx_packets++;
-		vif->dev->stats.tx_bytes += skb->len;
+		vif_dev->stats.tx_packets++;
+		vif_dev->stats.tx_bytes += skb->len;
 	}
 
 	IPCB(skb)->flags |= IPSKB_FORWARDED;
@@ -1906,18 +1920,20 @@ out_free:
 	kfree_skb(skb);
 }
 
-static int ipmr_find_vif(struct mr_table *mrt, struct net_device *dev)
+/* Called with mrt_lock or rcu_read_lock() */
+static int ipmr_find_vif(const struct mr_table *mrt, struct net_device *dev)
 {
 	int ct;
-
-	for (ct = mrt->maxvif-1; ct >= 0; ct--) {
-		if (mrt->vif_table[ct].dev == dev)
+	/* Pairs with WRITE_ONCE() in vif_delete()/vif_add() */
+	for (ct = READ_ONCE(mrt->maxvif) - 1; ct >= 0; ct--) {
+		if (rcu_access_pointer(mrt->vif_table[ct].dev) == dev)
 			break;
 	}
 	return ct;
 }
 
 /* "local" means that we should preserve one skb (for local delivery) */
+/* Called uner rcu_read_lock() */
 static void ip_mr_forward(struct net *net, struct mr_table *mrt,
 			  struct net_device *dev, struct sk_buff *skb,
 			  struct mfc_cache *c, int local)
@@ -1944,7 +1960,7 @@ static void ip_mr_forward(struct net *net, struct mr_table *mrt,
 	}
 
 	/* Wrong interface: drop packet and (maybe) send PIM assert. */
-	if (mrt->vif_table[vif].dev != dev) {
+	if (rcu_access_pointer(mrt->vif_table[vif].dev) != dev) {
 		if (rt_is_output_route(skb_rtable(skb))) {
 			/* It is our own packet, looped back.
 			 * Very complicated situation...
@@ -1983,8 +1999,10 @@ static void ip_mr_forward(struct net *net, struct mr_table *mrt,
 	}
 
 forward:
-	mrt->vif_table[vif].pkt_in++;
-	mrt->vif_table[vif].bytes_in += skb->len;
+	WRITE_ONCE(mrt->vif_table[vif].pkt_in,
+		   mrt->vif_table[vif].pkt_in + 1);
+	WRITE_ONCE(mrt->vif_table[vif].bytes_in,
+		   mrt->vif_table[vif].bytes_in + skb->len);
 
 	/* Forward the frame */
 	if (c->mfc_origin == htonl(INADDR_ANY) &&
@@ -2140,22 +2158,14 @@ int ip_mr_input(struct sk_buff *skb)
 			skb = skb2;
 		}
 
-		read_lock(&mrt_lock);
 		vif = ipmr_find_vif(mrt, dev);
-		if (vif >= 0) {
-			int err2 = ipmr_cache_unresolved(mrt, vif, skb, dev);
-			read_unlock(&mrt_lock);
-
-			return err2;
-		}
-		read_unlock(&mrt_lock);
+		if (vif >= 0)
+			return ipmr_cache_unresolved(mrt, vif, skb, dev);
 		kfree_skb(skb);
 		return -ENODEV;
 	}
 
-	read_lock(&mrt_lock);
 	ip_mr_forward(net, mrt, dev, skb, cache, local);
-	read_unlock(&mrt_lock);
 
 	if (local)
 		return ip_local_deliver(skb);
@@ -2252,18 +2262,15 @@ int ipmr_get_route(struct net *net, struct sk_buff *skb,
 		int vif = -1;
 
 		dev = skb->dev;
-		read_lock(&mrt_lock);
 		if (dev)
 			vif = ipmr_find_vif(mrt, dev);
 		if (vif < 0) {
-			read_unlock(&mrt_lock);
 			rcu_read_unlock();
 			return -ENODEV;
 		}
 
 		skb2 = skb_realloc_headroom(skb, sizeof(struct iphdr));
 		if (!skb2) {
-			read_unlock(&mrt_lock);
 			rcu_read_unlock();
 			return -ENOMEM;
 		}
@@ -2277,14 +2284,11 @@ int ipmr_get_route(struct net *net, struct sk_buff *skb,
 		iph->daddr = daddr;
 		iph->version = 0;
 		err = ipmr_cache_unresolved(mrt, vif, skb2, dev);
-		read_unlock(&mrt_lock);
 		rcu_read_unlock();
 		return err;
 	}
 
-	read_lock(&mrt_lock);
 	err = mr_fill_mroute(mrt, skb, &cache->_c, rtm);
-	read_unlock(&mrt_lock);
 	rcu_read_unlock();
 	return err;
 }
@@ -2404,7 +2408,7 @@ static size_t igmpmsg_netlink_msgsize(size_t payloadlen)
 	return len;
 }
 
-static void igmpmsg_netlink_event(struct mr_table *mrt, struct sk_buff *pkt)
+static void igmpmsg_netlink_event(const struct mr_table *mrt, struct sk_buff *pkt)
 {
 	struct net *net = read_pnet(&mrt->net);
 	struct nlmsghdr *nlh;
@@ -2744,18 +2748,21 @@ static bool ipmr_fill_table(struct mr_table *mrt, struct sk_buff *skb)
 
 static bool ipmr_fill_vif(struct mr_table *mrt, u32 vifid, struct sk_buff *skb)
 {
+	struct net_device *vif_dev;
 	struct nlattr *vif_nest;
 	struct vif_device *vif;
 
+	vif = &mrt->vif_table[vifid];
+	vif_dev = vif_dev_read(vif);
 	/* if the VIF doesn't exist just continue */
-	if (!VIF_EXISTS(mrt, vifid))
+	if (!vif_dev)
 		return true;
 
-	vif = &mrt->vif_table[vifid];
 	vif_nest = nla_nest_start_noflag(skb, IPMRA_VIF);
 	if (!vif_nest)
 		return false;
-	if (nla_put_u32(skb, IPMRA_VIFA_IFINDEX, vif->dev->ifindex) ||
+
+	if (nla_put_u32(skb, IPMRA_VIFA_IFINDEX, vif_dev->ifindex) ||
 	    nla_put_u32(skb, IPMRA_VIFA_VIF_ID, vifid) ||
 	    nla_put_u16(skb, IPMRA_VIFA_FLAGS, vif->flags) ||
 	    nla_put_u64_64bit(skb, IPMRA_VIFA_BYTES_IN, vif->bytes_in,
@@ -2887,7 +2894,7 @@ out:
  */
 
 static void *ipmr_vif_seq_start(struct seq_file *seq, loff_t *pos)
-	__acquires(mrt_lock)
+	__acquires(RCU)
 {
 	struct mr_vif_iter *iter = seq->private;
 	struct net *net = seq_file_net(seq);
@@ -2899,14 +2906,14 @@ static void *ipmr_vif_seq_start(struct seq_file *seq, loff_t *pos)
 
 	iter->mrt = mrt;
 
-	read_lock(&mrt_lock);
+	rcu_read_lock();
 	return mr_vif_seq_start(seq, pos);
 }
 
 static void ipmr_vif_seq_stop(struct seq_file *seq, void *v)
-	__releases(mrt_lock)
+	__releases(RCU)
 {
-	read_unlock(&mrt_lock);
+	rcu_read_unlock();
 }
 
 static int ipmr_vif_seq_show(struct seq_file *seq, void *v)
@@ -2919,9 +2926,11 @@ static int ipmr_vif_seq_show(struct seq_file *seq, void *v)
 			 "Interface      BytesIn  PktsIn  BytesOut PktsOut Flags Local    Remote\n");
 	} else {
 		const struct vif_device *vif = v;
-		const char *name =  vif->dev ?
-				    vif->dev->name : "none";
+		const struct net_device *vif_dev;
+		const char *name;
 
+		vif_dev = vif_dev_read(vif);
+		name = vif_dev ? vif_dev->name : "none";
 		seq_printf(seq,
 			   "%2td %-10s %8ld %7ld  %8ld %7ld %05X %08X %08X\n",
 			   vif - mrt->vif_table,
@@ -3017,7 +3026,7 @@ static int ipmr_dump(struct net *net, struct notifier_block *nb,
 		     struct netlink_ext_ack *extack)
 {
 	return mr_dump(net, nb, RTNL_FAMILY_IPMR, ipmr_rules_dump,
-		       ipmr_mr_table_iter, &mrt_lock, extack);
+		       ipmr_mr_table_iter, extack);
 }
 
 static const struct fib_notifier_ops ipmr_notifier_ops_template = {
diff --git a/net/ipv4/ipmr_base.c b/net/ipv4/ipmr_base.c
index aa8738a91210..271dc03fc6db 100644
--- a/net/ipv4/ipmr_base.c
+++ b/net/ipv4/ipmr_base.c
@@ -13,7 +13,7 @@ void vif_device_init(struct vif_device *v,
 		     unsigned short flags,
 		     unsigned short get_iflink_mask)
 {
-	v->dev = NULL;
+	RCU_INIT_POINTER(v->dev, NULL);
 	v->bytes_in = 0;
 	v->bytes_out = 0;
 	v->pkt_in = 0;
@@ -208,6 +208,7 @@ EXPORT_SYMBOL(mr_mfc_seq_next);
 int mr_fill_mroute(struct mr_table *mrt, struct sk_buff *skb,
 		   struct mr_mfc *c, struct rtmsg *rtm)
 {
+	struct net_device *vif_dev;
 	struct rta_mfc_stats mfcs;
 	struct nlattr *mp_attr;
 	struct rtnexthop *nhp;
@@ -220,10 +221,13 @@ int mr_fill_mroute(struct mr_table *mrt, struct sk_buff *skb,
 		return -ENOENT;
 	}
 
-	if (VIF_EXISTS(mrt, c->mfc_parent) &&
-	    nla_put_u32(skb, RTA_IIF,
-			mrt->vif_table[c->mfc_parent].dev->ifindex) < 0)
+	rcu_read_lock();
+	vif_dev = rcu_dereference(mrt->vif_table[c->mfc_parent].dev);
+	if (vif_dev && nla_put_u32(skb, RTA_IIF, vif_dev->ifindex) < 0) {
+		rcu_read_unlock();
 		return -EMSGSIZE;
+	}
+	rcu_read_unlock();
 
 	if (c->mfc_flags & MFC_OFFLOAD)
 		rtm->rtm_flags |= RTNH_F_OFFLOAD;
@@ -232,23 +236,27 @@ int mr_fill_mroute(struct mr_table *mrt, struct sk_buff *skb,
 	if (!mp_attr)
 		return -EMSGSIZE;
 
+	rcu_read_lock();
 	for (ct = c->mfc_un.res.minvif; ct < c->mfc_un.res.maxvif; ct++) {
-		if (VIF_EXISTS(mrt, ct) && c->mfc_un.res.ttls[ct] < 255) {
-			struct vif_device *vif;
+		struct vif_device *vif = &mrt->vif_table[ct];
+
+		vif_dev = rcu_dereference(vif->dev);
+		if (vif_dev && c->mfc_un.res.ttls[ct] < 255) {
 
 			nhp = nla_reserve_nohdr(skb, sizeof(*nhp));
 			if (!nhp) {
+				rcu_read_unlock();
 				nla_nest_cancel(skb, mp_attr);
 				return -EMSGSIZE;
 			}
 
 			nhp->rtnh_flags = 0;
 			nhp->rtnh_hops = c->mfc_un.res.ttls[ct];
-			vif = &mrt->vif_table[ct];
-			nhp->rtnh_ifindex = vif->dev->ifindex;
+			nhp->rtnh_ifindex = vif_dev->ifindex;
 			nhp->rtnh_len = sizeof(*nhp);
 		}
 	}
+	rcu_read_unlock();
 
 	nla_nest_end(skb, mp_attr);
 
@@ -275,13 +283,14 @@ static bool mr_mfc_uses_dev(const struct mr_table *mrt,
 	int ct;
 
 	for (ct = c->mfc_un.res.minvif; ct < c->mfc_un.res.maxvif; ct++) {
-		if (VIF_EXISTS(mrt, ct) && c->mfc_un.res.ttls[ct] < 255) {
-			const struct vif_device *vif;
-
-			vif = &mrt->vif_table[ct];
-			if (vif->dev == dev)
-				return true;
-		}
+		const struct net_device *vif_dev;
+		const struct vif_device *vif;
+
+		vif = &mrt->vif_table[ct];
+		vif_dev = rcu_access_pointer(vif->dev);
+		if (vif_dev && c->mfc_un.res.ttls[ct] < 255 &&
+		    vif_dev == dev)
+			return true;
 	}
 	return false;
 }
@@ -390,7 +399,6 @@ int mr_dump(struct net *net, struct notifier_block *nb, unsigned short family,
 			      struct netlink_ext_ack *extack),
 	    struct mr_table *(*mr_iter)(struct net *net,
 					struct mr_table *mrt),
-	    rwlock_t *mrt_lock,
 	    struct netlink_ext_ack *extack)
 {
 	struct mr_table *mrt;
@@ -402,22 +410,25 @@ int mr_dump(struct net *net, struct notifier_block *nb, unsigned short family,
 
 	for (mrt = mr_iter(net, NULL); mrt; mrt = mr_iter(net, mrt)) {
 		struct vif_device *v = &mrt->vif_table[0];
+		struct net_device *vif_dev;
 		struct mr_mfc *mfc;
 		int vifi;
 
 		/* Notifiy on table VIF entries */
-		read_lock(mrt_lock);
+		rcu_read_lock();
 		for (vifi = 0; vifi < mrt->maxvif; vifi++, v++) {
-			if (!v->dev)
+			vif_dev = rcu_dereference(v->dev);
+			if (!vif_dev)
 				continue;
 
 			err = mr_call_vif_notifier(nb, family,
-						   FIB_EVENT_VIF_ADD,
-						   v, vifi, mrt->id, extack);
+						   FIB_EVENT_VIF_ADD, v,
+						   vif_dev, vifi,
+						   mrt->id, extack);
 			if (err)
 				break;
 		}
-		read_unlock(mrt_lock);
+		rcu_read_unlock();
 
 		if (err)
 			return err;
diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c
index d4aad41c9849..ec6e1509fc7c 100644
--- a/net/ipv6/ip6mr.c
+++ b/net/ipv6/ip6mr.c
@@ -62,7 +62,12 @@ struct ip6mr_result {
    Note that the changes are semaphored via rtnl_lock.
  */
 
-static DEFINE_RWLOCK(mrt_lock);
+static DEFINE_SPINLOCK(mrt_lock);
+
+static struct net_device *vif_dev_read(const struct vif_device *vif)
+{
+	return rcu_dereference(vif->dev);
+}
 
 /* Multicast router control variables */
 
@@ -85,11 +90,11 @@ static void ip6mr_free_table(struct mr_table *mrt);
 static void ip6_mr_forward(struct net *net, struct mr_table *mrt,
 			   struct net_device *dev, struct sk_buff *skb,
 			   struct mfc6_cache *cache);
-static int ip6mr_cache_report(struct mr_table *mrt, struct sk_buff *pkt,
+static int ip6mr_cache_report(const struct mr_table *mrt, struct sk_buff *pkt,
 			      mifi_t mifi, int assert);
 static void mr6_netlink_event(struct mr_table *mrt, struct mfc6_cache *mfc,
 			      int cmd);
-static void mrt6msg_netlink_event(struct mr_table *mrt, struct sk_buff *pkt);
+static void mrt6msg_netlink_event(const struct mr_table *mrt, struct sk_buff *pkt);
 static int ip6mr_rtm_dumproute(struct sk_buff *skb,
 			       struct netlink_callback *cb);
 static void mroute_clean_tables(struct mr_table *mrt, int flags);
@@ -398,7 +403,7 @@ static void ip6mr_free_table(struct mr_table *mrt)
  */
 
 static void *ip6mr_vif_seq_start(struct seq_file *seq, loff_t *pos)
-	__acquires(mrt_lock)
+	__acquires(RCU)
 {
 	struct mr_vif_iter *iter = seq->private;
 	struct net *net = seq_file_net(seq);
@@ -410,14 +415,14 @@ static void *ip6mr_vif_seq_start(struct seq_file *seq, loff_t *pos)
 
 	iter->mrt = mrt;
 
-	read_lock(&mrt_lock);
+	rcu_read_lock();
 	return mr_vif_seq_start(seq, pos);
 }
 
 static void ip6mr_vif_seq_stop(struct seq_file *seq, void *v)
-	__releases(mrt_lock)
+	__releases(RCU)
 {
-	read_unlock(&mrt_lock);
+	rcu_read_unlock();
 }
 
 static int ip6mr_vif_seq_show(struct seq_file *seq, void *v)
@@ -430,7 +435,11 @@ static int ip6mr_vif_seq_show(struct seq_file *seq, void *v)
 			 "Interface      BytesIn  PktsIn  BytesOut PktsOut Flags\n");
 	} else {
 		const struct vif_device *vif = v;
-		const char *name = vif->dev ? vif->dev->name : "none";
+		const struct net_device *vif_dev;
+		const char *name;
+
+		vif_dev = vif_dev_read(vif);
+		name = vif_dev ? vif_dev->name : "none";
 
 		seq_printf(seq,
 			   "%2td %-10s %8ld %7ld  %8ld %7ld %05X\n",
@@ -549,13 +558,11 @@ static int pim6_rcv(struct sk_buff *skb)
 
 	if (ip6mr_fib_lookup(net, &fl6, &mrt) < 0)
 		goto drop;
-	reg_vif_num = mrt->mroute_reg_vif_num;
 
-	read_lock(&mrt_lock);
+	/* Pairs with WRITE_ONCE() in mif6_add()/mif6_delete() */
+	reg_vif_num = READ_ONCE(mrt->mroute_reg_vif_num);
 	if (reg_vif_num >= 0)
-		reg_dev = mrt->vif_table[reg_vif_num].dev;
-	dev_hold(reg_dev);
-	read_unlock(&mrt_lock);
+		reg_dev = vif_dev_read(&mrt->vif_table[reg_vif_num]);
 
 	if (!reg_dev)
 		goto drop;
@@ -570,7 +577,6 @@ static int pim6_rcv(struct sk_buff *skb)
 
 	netif_rx(skb);
 
-	dev_put(reg_dev);
 	return 0;
  drop:
 	kfree_skb(skb);
@@ -600,11 +606,12 @@ static netdev_tx_t reg_vif_xmit(struct sk_buff *skb,
 	if (ip6mr_fib_lookup(net, &fl6, &mrt) < 0)
 		goto tx_err;
 
-	read_lock(&mrt_lock);
 	dev->stats.tx_bytes += skb->len;
 	dev->stats.tx_packets++;
-	ip6mr_cache_report(mrt, skb, mrt->mroute_reg_vif_num, MRT6MSG_WHOLEPKT);
-	read_unlock(&mrt_lock);
+	rcu_read_lock();
+	ip6mr_cache_report(mrt, skb, READ_ONCE(mrt->mroute_reg_vif_num),
+			   MRT6MSG_WHOLEPKT);
+	rcu_read_unlock();
 	kfree_skb(skb);
 	return NETDEV_TX_OK;
 
@@ -670,10 +677,11 @@ failure:
 static int call_ip6mr_vif_entry_notifiers(struct net *net,
 					  enum fib_event_type event_type,
 					  struct vif_device *vif,
+					  struct net_device *vif_dev,
 					  mifi_t vif_index, u32 tb_id)
 {
 	return mr_call_vif_notifiers(net, RTNL_FAMILY_IP6MR, event_type,
-				     vif, vif_index, tb_id,
+				     vif, vif_dev, vif_index, tb_id,
 				     &net->ipv6.ipmr_seq);
 }
 
@@ -698,23 +706,21 @@ static int mif6_delete(struct mr_table *mrt, int vifi, int notify,
 
 	v = &mrt->vif_table[vifi];
 
-	if (VIF_EXISTS(mrt, vifi))
-		call_ip6mr_vif_entry_notifiers(read_pnet(&mrt->net),
-					       FIB_EVENT_VIF_DEL, v, vifi,
-					       mrt->id);
-
-	write_lock_bh(&mrt_lock);
-	dev = v->dev;
-	v->dev = NULL;
-
-	if (!dev) {
-		write_unlock_bh(&mrt_lock);
+	dev = rtnl_dereference(v->dev);
+	if (!dev)
 		return -EADDRNOTAVAIL;
-	}
+
+	call_ip6mr_vif_entry_notifiers(read_pnet(&mrt->net),
+				       FIB_EVENT_VIF_DEL, v, dev,
+				       vifi, mrt->id);
+	spin_lock(&mrt_lock);
+	RCU_INIT_POINTER(v->dev, NULL);
 
 #ifdef CONFIG_IPV6_PIMSM_V2
-	if (vifi == mrt->mroute_reg_vif_num)
-		mrt->mroute_reg_vif_num = -1;
+	if (vifi == mrt->mroute_reg_vif_num) {
+		/* Pairs with READ_ONCE() in ip6mr_cache_report() and reg_vif_xmit() */
+		WRITE_ONCE(mrt->mroute_reg_vif_num, -1);
+	}
 #endif
 
 	if (vifi + 1 == mrt->maxvif) {
@@ -723,10 +729,10 @@ static int mif6_delete(struct mr_table *mrt, int vifi, int notify,
 			if (VIF_EXISTS(mrt, tmp))
 				break;
 		}
-		mrt->maxvif = tmp + 1;
+		WRITE_ONCE(mrt->maxvif, tmp + 1);
 	}
 
-	write_unlock_bh(&mrt_lock);
+	spin_unlock(&mrt_lock);
 
 	dev_set_allmulti(dev, -1);
 
@@ -826,7 +832,7 @@ static void ipmr_expire_process(struct timer_list *t)
 	spin_unlock(&mfc_unres_lock);
 }
 
-/* Fill oifs list. It is called under write locked mrt_lock. */
+/* Fill oifs list. It is called under locked mrt_lock. */
 
 static void ip6mr_update_thresholds(struct mr_table *mrt,
 				    struct mr_mfc *cache,
@@ -912,18 +918,18 @@ static int mif6_add(struct net *net, struct mr_table *mrt,
 			MIFF_REGISTER);
 
 	/* And finish update writing critical data */
-	write_lock_bh(&mrt_lock);
-	v->dev = dev;
+	spin_lock(&mrt_lock);
+	rcu_assign_pointer(v->dev, dev);
 	netdev_tracker_alloc(dev, &v->dev_tracker, GFP_ATOMIC);
 #ifdef CONFIG_IPV6_PIMSM_V2
 	if (v->flags & MIFF_REGISTER)
-		mrt->mroute_reg_vif_num = vifi;
+		WRITE_ONCE(mrt->mroute_reg_vif_num, vifi);
 #endif
 	if (vifi + 1 > mrt->maxvif)
-		mrt->maxvif = vifi + 1;
-	write_unlock_bh(&mrt_lock);
+		WRITE_ONCE(mrt->maxvif, vifi + 1);
+	spin_unlock(&mrt_lock);
 	call_ip6mr_vif_entry_notifiers(net, FIB_EVENT_VIF_ADD,
-				       v, vifi, mrt->id);
+				       v, dev, vifi, mrt->id);
 	return 0;
 }
 
@@ -1028,10 +1034,10 @@ static void ip6mr_cache_resolve(struct net *net, struct mr_table *mrt,
 /*
  *	Bounce a cache query up to pim6sd and netlink.
  *
- *	Called under mrt_lock.
+ *	Called under rcu_read_lock()
  */
 
-static int ip6mr_cache_report(struct mr_table *mrt, struct sk_buff *pkt,
+static int ip6mr_cache_report(const struct mr_table *mrt, struct sk_buff *pkt,
 			      mifi_t mifi, int assert)
 {
 	struct sock *mroute6_sk;
@@ -1072,7 +1078,7 @@ static int ip6mr_cache_report(struct mr_table *mrt, struct sk_buff *pkt,
 		if (assert == MRT6MSG_WRMIFWHOLE)
 			msg->im6_mif = mifi;
 		else
-			msg->im6_mif = mrt->mroute_reg_vif_num;
+			msg->im6_mif = READ_ONCE(mrt->mroute_reg_vif_num);
 		msg->im6_pad = 0;
 		msg->im6_src = ipv6_hdr(pkt)->saddr;
 		msg->im6_dst = ipv6_hdr(pkt)->daddr;
@@ -1107,10 +1113,8 @@ static int ip6mr_cache_report(struct mr_table *mrt, struct sk_buff *pkt,
 	skb->ip_summed = CHECKSUM_UNNECESSARY;
 	}
 
-	rcu_read_lock();
 	mroute6_sk = rcu_dereference(mrt->mroute_sk);
 	if (!mroute6_sk) {
-		rcu_read_unlock();
 		kfree_skb(skb);
 		return -EINVAL;
 	}
@@ -1119,7 +1123,7 @@ static int ip6mr_cache_report(struct mr_table *mrt, struct sk_buff *pkt,
 
 	/* Deliver to user space multicast routing algorithms */
 	ret = sock_queue_rcv_skb(mroute6_sk, skb);
-	rcu_read_unlock();
+
 	if (ret < 0) {
 		net_warn_ratelimited("mroute6: pending queue full, dropping entries\n");
 		kfree_skb(skb);
@@ -1243,7 +1247,7 @@ static int ip6mr_device_event(struct notifier_block *this,
 	ip6mr_for_each_table(mrt, net) {
 		v = &mrt->vif_table[0];
 		for (ct = 0; ct < mrt->maxvif; ct++, v++) {
-			if (v->dev == dev)
+			if (rcu_access_pointer(v->dev) == dev)
 				mif6_delete(mrt, ct, 1, NULL);
 		}
 	}
@@ -1262,7 +1266,7 @@ static int ip6mr_dump(struct net *net, struct notifier_block *nb,
 		      struct netlink_ext_ack *extack)
 {
 	return mr_dump(net, nb, RTNL_FAMILY_IP6MR, ip6mr_rules_dump,
-		       ip6mr_mr_table_iter, &mrt_lock, extack);
+		       ip6mr_mr_table_iter, extack);
 }
 
 static struct notifier_block ip6_mr_notifier = {
@@ -1437,12 +1441,12 @@ static int ip6mr_mfc_add(struct net *net, struct mr_table *mrt,
 				    &mfc->mf6cc_mcastgrp.sin6_addr, parent);
 	rcu_read_unlock();
 	if (c) {
-		write_lock_bh(&mrt_lock);
+		spin_lock(&mrt_lock);
 		c->_c.mfc_parent = mfc->mf6cc_parent;
 		ip6mr_update_thresholds(mrt, &c->_c, ttls);
 		if (!mrtsock)
 			c->_c.mfc_flags |= MFC_STATIC;
-		write_unlock_bh(&mrt_lock);
+		spin_unlock(&mrt_lock);
 		call_ip6mr_mfc_entry_notifiers(net, FIB_EVENT_ENTRY_REPLACE,
 					       c, mrt->id);
 		mr6_netlink_event(mrt, c, RTM_NEWROUTE);
@@ -1560,7 +1564,7 @@ static int ip6mr_sk_init(struct mr_table *mrt, struct sock *sk)
 	struct net *net = sock_net(sk);
 
 	rtnl_lock();
-	write_lock_bh(&mrt_lock);
+	spin_lock(&mrt_lock);
 	if (rtnl_dereference(mrt->mroute_sk)) {
 		err = -EADDRINUSE;
 	} else {
@@ -1568,7 +1572,7 @@ static int ip6mr_sk_init(struct mr_table *mrt, struct sock *sk)
 		sock_set_flag(sk, SOCK_RCU_FREE);
 		atomic_inc(&net->ipv6.devconf_all->mc_forwarding);
 	}
-	write_unlock_bh(&mrt_lock);
+	spin_unlock(&mrt_lock);
 
 	if (!err)
 		inet6_netconf_notify_devconf(net, RTM_NEWNETCONF,
@@ -1598,14 +1602,14 @@ int ip6mr_sk_done(struct sock *sk)
 	rtnl_lock();
 	ip6mr_for_each_table(mrt, net) {
 		if (sk == rtnl_dereference(mrt->mroute_sk)) {
-			write_lock_bh(&mrt_lock);
+			spin_lock(&mrt_lock);
 			RCU_INIT_POINTER(mrt->mroute_sk, NULL);
 			/* Note that mroute_sk had SOCK_RCU_FREE set,
 			 * so the RCU grace period before sk freeing
 			 * is guaranteed by sk_destruct()
 			 */
 			atomic_dec(&devconf->mc_forwarding);
-			write_unlock_bh(&mrt_lock);
+			spin_unlock(&mrt_lock);
 			inet6_netconf_notify_devconf(net, RTM_NEWNETCONF,
 						     NETCONFA_MC_FORWARDING,
 						     NETCONFA_IFINDEX_ALL,
@@ -1891,20 +1895,20 @@ int ip6mr_ioctl(struct sock *sk, int cmd, void __user *arg)
 		if (vr.mifi >= mrt->maxvif)
 			return -EINVAL;
 		vr.mifi = array_index_nospec(vr.mifi, mrt->maxvif);
-		read_lock(&mrt_lock);
+		rcu_read_lock();
 		vif = &mrt->vif_table[vr.mifi];
 		if (VIF_EXISTS(mrt, vr.mifi)) {
-			vr.icount = vif->pkt_in;
-			vr.ocount = vif->pkt_out;
-			vr.ibytes = vif->bytes_in;
-			vr.obytes = vif->bytes_out;
-			read_unlock(&mrt_lock);
+			vr.icount = READ_ONCE(vif->pkt_in);
+			vr.ocount = READ_ONCE(vif->pkt_out);
+			vr.ibytes = READ_ONCE(vif->bytes_in);
+			vr.obytes = READ_ONCE(vif->bytes_out);
+			rcu_read_unlock();
 
 			if (copy_to_user(arg, &vr, sizeof(vr)))
 				return -EFAULT;
 			return 0;
 		}
-		read_unlock(&mrt_lock);
+		rcu_read_unlock();
 		return -EADDRNOTAVAIL;
 	case SIOCGETSGCNT_IN6:
 		if (copy_from_user(&sr, arg, sizeof(sr)))
@@ -1966,20 +1970,20 @@ int ip6mr_compat_ioctl(struct sock *sk, unsigned int cmd, void __user *arg)
 		if (vr.mifi >= mrt->maxvif)
 			return -EINVAL;
 		vr.mifi = array_index_nospec(vr.mifi, mrt->maxvif);
-		read_lock(&mrt_lock);
+		rcu_read_lock();
 		vif = &mrt->vif_table[vr.mifi];
 		if (VIF_EXISTS(mrt, vr.mifi)) {
-			vr.icount = vif->pkt_in;
-			vr.ocount = vif->pkt_out;
-			vr.ibytes = vif->bytes_in;
-			vr.obytes = vif->bytes_out;
-			read_unlock(&mrt_lock);
+			vr.icount = READ_ONCE(vif->pkt_in);
+			vr.ocount = READ_ONCE(vif->pkt_out);
+			vr.ibytes = READ_ONCE(vif->bytes_in);
+			vr.obytes = READ_ONCE(vif->bytes_out);
+			rcu_read_unlock();
 
 			if (copy_to_user(arg, &vr, sizeof(vr)))
 				return -EFAULT;
 			return 0;
 		}
-		read_unlock(&mrt_lock);
+		rcu_read_unlock();
 		return -EADDRNOTAVAIL;
 	case SIOCGETSGCNT_IN6:
 		if (copy_from_user(&sr, arg, sizeof(sr)))
@@ -2021,21 +2025,22 @@ static inline int ip6mr_forward2_finish(struct net *net, struct sock *sk, struct
 static int ip6mr_forward2(struct net *net, struct mr_table *mrt,
 			  struct sk_buff *skb, int vifi)
 {
-	struct ipv6hdr *ipv6h;
 	struct vif_device *vif = &mrt->vif_table[vifi];
-	struct net_device *dev;
+	struct net_device *vif_dev;
+	struct ipv6hdr *ipv6h;
 	struct dst_entry *dst;
 	struct flowi6 fl6;
 
-	if (!vif->dev)
+	vif_dev = vif_dev_read(vif);
+	if (!vif_dev)
 		goto out_free;
 
 #ifdef CONFIG_IPV6_PIMSM_V2
 	if (vif->flags & MIFF_REGISTER) {
-		vif->pkt_out++;
-		vif->bytes_out += skb->len;
-		vif->dev->stats.tx_bytes += skb->len;
-		vif->dev->stats.tx_packets++;
+		WRITE_ONCE(vif->pkt_out, vif->pkt_out + 1);
+		WRITE_ONCE(vif->bytes_out, vif->bytes_out + skb->len);
+		vif_dev->stats.tx_bytes += skb->len;
+		vif_dev->stats.tx_packets++;
 		ip6mr_cache_report(mrt, skb, vifi, MRT6MSG_WHOLEPKT);
 		goto out_free;
 	}
@@ -2068,14 +2073,13 @@ static int ip6mr_forward2(struct net *net, struct mr_table *mrt,
 	 * not mrouter) cannot join to more than one interface - it will
 	 * result in receiving multiple packets.
 	 */
-	dev = vif->dev;
-	skb->dev = dev;
-	vif->pkt_out++;
-	vif->bytes_out += skb->len;
+	skb->dev = vif_dev;
+	WRITE_ONCE(vif->pkt_out, vif->pkt_out + 1);
+	WRITE_ONCE(vif->bytes_out, vif->bytes_out + skb->len);
 
 	/* We are about to write */
 	/* XXX: extension headers? */
-	if (skb_cow(skb, sizeof(*ipv6h) + LL_RESERVED_SPACE(dev)))
+	if (skb_cow(skb, sizeof(*ipv6h) + LL_RESERVED_SPACE(vif_dev)))
 		goto out_free;
 
 	ipv6h = ipv6_hdr(skb);
@@ -2084,7 +2088,7 @@ static int ip6mr_forward2(struct net *net, struct mr_table *mrt,
 	IP6CB(skb)->flags |= IP6SKB_FORWARDED;
 
 	return NF_HOOK(NFPROTO_IPV6, NF_INET_FORWARD,
-		       net, NULL, skb, skb->dev, dev,
+		       net, NULL, skb, skb->dev, vif_dev,
 		       ip6mr_forward2_finish);
 
 out_free:
@@ -2092,17 +2096,20 @@ out_free:
 	return 0;
 }
 
+/* Called with rcu_read_lock() */
 static int ip6mr_find_vif(struct mr_table *mrt, struct net_device *dev)
 {
 	int ct;
 
-	for (ct = mrt->maxvif - 1; ct >= 0; ct--) {
-		if (mrt->vif_table[ct].dev == dev)
+	/* Pairs with WRITE_ONCE() in mif6_delete()/mif6_add() */
+	for (ct = READ_ONCE(mrt->maxvif) - 1; ct >= 0; ct--) {
+		if (rcu_access_pointer(mrt->vif_table[ct].dev) == dev)
 			break;
 	}
 	return ct;
 }
 
+/* Called under rcu_read_lock() */
 static void ip6_mr_forward(struct net *net, struct mr_table *mrt,
 			   struct net_device *dev, struct sk_buff *skb,
 			   struct mfc6_cache *c)
@@ -2122,20 +2129,18 @@ static void ip6_mr_forward(struct net *net, struct mr_table *mrt,
 		/* For an (*,G) entry, we only check that the incoming
 		 * interface is part of the static tree.
 		 */
-		rcu_read_lock();
 		cache_proxy = mr_mfc_find_any_parent(mrt, vif);
 		if (cache_proxy &&
 		    cache_proxy->_c.mfc_un.res.ttls[true_vifi] < 255) {
 			rcu_read_unlock();
 			goto forward;
 		}
-		rcu_read_unlock();
 	}
 
 	/*
 	 * Wrong interface: drop packet and (maybe) send PIM assert.
 	 */
-	if (mrt->vif_table[vif].dev != dev) {
+	if (rcu_access_pointer(mrt->vif_table[vif].dev) != dev) {
 		c->_c.mfc_un.res.wrong_if++;
 
 		if (true_vifi >= 0 && mrt->mroute_do_assert &&
@@ -2159,8 +2164,10 @@ static void ip6_mr_forward(struct net *net, struct mr_table *mrt,
 	}
 
 forward:
-	mrt->vif_table[vif].pkt_in++;
-	mrt->vif_table[vif].bytes_in += skb->len;
+	WRITE_ONCE(mrt->vif_table[vif].pkt_in,
+		   mrt->vif_table[vif].pkt_in + 1);
+	WRITE_ONCE(mrt->vif_table[vif].bytes_in,
+		   mrt->vif_table[vif].bytes_in + skb->len);
 
 	/*
 	 *	Forward the frame
@@ -2238,7 +2245,6 @@ int ip6_mr_input(struct sk_buff *skb)
 		return err;
 	}
 
-	read_lock(&mrt_lock);
 	cache = ip6mr_cache_find(mrt,
 				 &ipv6_hdr(skb)->saddr, &ipv6_hdr(skb)->daddr);
 	if (!cache) {
@@ -2259,19 +2265,15 @@ int ip6_mr_input(struct sk_buff *skb)
 		vif = ip6mr_find_vif(mrt, dev);
 		if (vif >= 0) {
 			int err = ip6mr_cache_unresolved(mrt, vif, skb, dev);
-			read_unlock(&mrt_lock);
 
 			return err;
 		}
-		read_unlock(&mrt_lock);
 		kfree_skb(skb);
 		return -ENODEV;
 	}
 
 	ip6_mr_forward(net, mrt, dev, skb, cache);
 
-	read_unlock(&mrt_lock);
-
 	return 0;
 }
 
@@ -2287,7 +2289,7 @@ int ip6mr_get_route(struct net *net, struct sk_buff *skb, struct rtmsg *rtm,
 	if (!mrt)
 		return -ENOENT;
 
-	read_lock(&mrt_lock);
+	rcu_read_lock();
 	cache = ip6mr_cache_find(mrt, &rt->rt6i_src.addr, &rt->rt6i_dst.addr);
 	if (!cache && skb->dev) {
 		int vif = ip6mr_find_vif(mrt, skb->dev);
@@ -2305,14 +2307,14 @@ int ip6mr_get_route(struct net *net, struct sk_buff *skb, struct rtmsg *rtm,
 
 		dev = skb->dev;
 		if (!dev || (vif = ip6mr_find_vif(mrt, dev)) < 0) {
-			read_unlock(&mrt_lock);
+			rcu_read_unlock();
 			return -ENODEV;
 		}
 
 		/* really correct? */
 		skb2 = alloc_skb(sizeof(struct ipv6hdr), GFP_ATOMIC);
 		if (!skb2) {
-			read_unlock(&mrt_lock);
+			rcu_read_unlock();
 			return -ENOMEM;
 		}
 
@@ -2335,13 +2337,13 @@ int ip6mr_get_route(struct net *net, struct sk_buff *skb, struct rtmsg *rtm,
 		iph->daddr = rt->rt6i_dst.addr;
 
 		err = ip6mr_cache_unresolved(mrt, vif, skb2, dev);
-		read_unlock(&mrt_lock);
+		rcu_read_unlock();
 
 		return err;
 	}
 
 	err = mr_fill_mroute(mrt, skb, &cache->_c, rtm);
-	read_unlock(&mrt_lock);
+	rcu_read_unlock();
 	return err;
 }
 
@@ -2460,7 +2462,7 @@ static size_t mrt6msg_netlink_msgsize(size_t payloadlen)
 	return len;
 }
 
-static void mrt6msg_netlink_event(struct mr_table *mrt, struct sk_buff *pkt)
+static void mrt6msg_netlink_event(const struct mr_table *mrt, struct sk_buff *pkt)
 {
 	struct net *net = read_pnet(&mrt->net);
 	struct nlmsghdr *nlh;