vlan: remove one synchronize_net() call

At VLAN dismantle phase, unregister_vlan_dev() makes one
synchronize_net() call after vlan_group_set_device(grp, vlan_id, NULL).

This call can be safely removed because we are calling
unregister_netdevice_queue() to queue device for deletion, and this
process needs at least one rcu grace period to complete.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Ben Greear <greearb@candelatech.com>
Cc: Patrick McHardy <kaber@trash.net>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Jesse Gross <jesse@nicira.com>
Cc: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Acked-by: Jesse Gross <jesse@nicira.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 4 insertions, 7 deletions

diff --git a/include/linux/if_vlan.h b/include/linux/if_vlan.h
index 546d9d35fbd4..290bd8ac94cf 100644
--- a/include/linux/if_vlan.h
+++ b/include/linux/if_vlan.h
@@ -86,7 +86,6 @@ struct vlan_group {
                                             * the vlan is attached to.
                                             */
         unsigned int            nr_vlans;
-        int                     killall;
         struct hlist_node       hlist;  /* linked list */
         struct net_device **vlan_devices_arrays[VLAN_GROUP_ARRAY_SPLIT_PARTS];
         struct rcu_head         rcu;
diff --git a/net/8021q/vlan.c b/net/8021q/vlan.c
index 969e7004cf86..718d635d3379 100644
--- a/net/8021q/vlan.c
+++ b/net/8021q/vlan.c
@@ -120,9 +120,10 @@ void unregister_vlan_dev(struct net_device *dev, struct list_head *head)
         grp->nr_vlans--;
 
         vlan_group_set_device(grp, vlan_id, NULL);
-        if (!grp->killall)
-                synchronize_net();
-
+        /* Because unregister_netdevice_queue() makes sure at least one rcu
+         * grace period is respected before device freeing,
+         * we dont need to call synchronize_net() here.
+         */
         unregister_netdevice_queue(dev, head);
 
         /* If the group is now empty, kill off the group. */
@@ -478,9 +479,6 @@ static int vlan_device_event(struct notifier_block *unused, unsigned long event,
                 if (dev->reg_state != NETREG_UNREGISTERING)
                         break;
 
-                /* Delete all VLANs for this dev. */
-                grp->killall = 1;
-
                 for (i = 0; i < VLAN_N_VID; i++) {
                         vlandev = vlan_group_get_device(grp, i);
                         if (!vlandev)