net: Fix high overhead of vlan sub-device teardown.

When a networking device is taken down that has a non-trivial number
of VLAN devices configured under it, we eat a full synchronize_net()
for every such VLAN device.

This is because of the call chain:

	NETDEV_DOWN notifier
	--> vlan_device_event()
		--> dev_change_flags()
		--> __dev_change_flags()
		--> __dev_close()
		--> __dev_close_many()
		--> dev_deactivate_many()
			--> synchronize_net()

This is kind of rediculous because we already have infrastructure for
batching doing operation X to a list of net devices so that we only
incur one sync.

So make use of that by exporting dev_close_many() and adjusting it's
interfaace so that the caller can fully manage the batch list.  Use
this in vlan_device_event() and all the overhead goes away.

Reported-by: Salam Noureddine <noureddine@arista.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 20 insertions, 7 deletions

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index ec8f9b5f6500..76951c5fbedf 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -2156,6 +2156,7 @@ struct net_device *__dev_get_by_name(struct net *net, const char *name);
 int dev_alloc_name(struct net_device *dev, const char *name);
 int dev_open(struct net_device *dev);
 int dev_close(struct net_device *dev);
+int dev_close_many(struct list_head *head, bool unlink);
 void dev_disable_lro(struct net_device *dev);
 int dev_loopback_xmit(struct sk_buff *newskb);
 int dev_queue_xmit(struct sk_buff *skb);
diff --git a/net/8021q/vlan.c b/net/8021q/vlan.c
index 64c6bed4a3d3..98a30a5b8664 100644
--- a/net/8021q/vlan.c
+++ b/net/8021q/vlan.c
@@ -413,7 +413,10 @@ static int vlan_device_event(struct notifier_block *unused, unsigned long event,
                         vlan_transfer_features(dev, vlandev);
                 break;
 
-        case NETDEV_DOWN:
+        case NETDEV_DOWN: {
+                struct net_device *tmp;
+                LIST_HEAD(close_list);
+
                 if (dev->features & NETIF_F_HW_VLAN_CTAG_FILTER)
                         vlan_vid_del(dev, htons(ETH_P_8021Q), 0);
 
@@ -425,11 +428,18 @@ static int vlan_device_event(struct notifier_block *unused, unsigned long event,
 
                         vlan = vlan_dev_priv(vlandev);
                         if (!(vlan->flags & VLAN_FLAG_LOOSE_BINDING))
-                                dev_change_flags(vlandev, flgs & ~IFF_UP);
+                                list_add(&vlandev->close_list, &close_list);
+                }
+
+                dev_close_many(&close_list, false);
+
+                list_for_each_entry_safe(vlandev, tmp, &close_list, close_list) {
                         netif_stacked_transfer_operstate(dev, vlandev);
+                        list_del_init(&vlandev->close_list);
                 }
+                list_del(&close_list);
                 break;
-
+        }
         case NETDEV_UP:
                 /* Put all VLANs for this dev in the up state too.  */
                 vlan_group_for_each_dev(grp, i, vlandev) {
diff --git a/net/core/dev.c b/net/core/dev.c
index a1f24151db5b..5d43e010ef87 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1385,7 +1385,7 @@ static int __dev_close(struct net_device *dev)
         return retval;
 }
 
-static int dev_close_many(struct list_head *head)
+int dev_close_many(struct list_head *head, bool unlink)
 {
         struct net_device *dev, *tmp;
 
@@ -1399,11 +1399,13 @@ static int dev_close_many(struct list_head *head)
         list_for_each_entry_safe(dev, tmp, head, close_list) {
                 rtmsg_ifinfo(RTM_NEWLINK, dev, IFF_UP|IFF_RUNNING, GFP_KERNEL);
                 call_netdevice_notifiers(NETDEV_DOWN, dev);
-                list_del_init(&dev->close_list);
+                if (unlink)
+                        list_del_init(&dev->close_list);
         }
 
         return 0;
 }
+EXPORT_SYMBOL(dev_close_many);
 
 /**
  *      dev_close - shutdown an interface.
@@ -1420,7 +1422,7 @@ int dev_close(struct net_device *dev)
                 LIST_HEAD(single);
 
                 list_add(&dev->close_list, &single);
-                dev_close_many(&single);
+                dev_close_many(&single, true);
                 list_del(&single);
         }
         return 0;
@@ -5986,7 +5988,7 @@ static void rollback_registered_many(struct list_head *head)
         /* If device is running, close it first. */
         list_for_each_entry(dev, head, unreg_list)
                 list_add_tail(&dev->close_list, &close_head);
-        dev_close_many(&close_head);
+        dev_close_many(&close_head, true);
 
         list_for_each_entry(dev, head, unreg_list) {
                 /* And unlink it from device chain. */