macvlan: remove one synchronize_rcu() call

When one macvlan device is dismantled, we can avoid one
synchronize_rcu() call done after deletion from hash list, since caller
will perform a synchronize_net() call after its ndo_stop() call.

Add a new netdev->dismantle field to signal this dismantle intent.

Reduces RTNL hold time.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
CC: Patrick McHardy <kaber@trash.net>
CC: Ben Greear <greearb@candelatech.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 9 insertions, 6 deletions

diff --git a/drivers/net/macvlan.c b/drivers/net/macvlan.c
index d7c0bc62da7f..07bcb8084d78 100644
--- a/drivers/net/macvlan.c
+++ b/drivers/net/macvlan.c
@@ -70,16 +70,17 @@ static void macvlan_hash_add(struct macvlan_dev *vlan)
         hlist_add_head_rcu(&vlan->hlist, &port->vlan_hash[addr[5]]);
 }
 
-static void macvlan_hash_del(struct macvlan_dev *vlan)
+static void macvlan_hash_del(struct macvlan_dev *vlan, bool sync)
 {
         hlist_del_rcu(&vlan->hlist);
-        synchronize_rcu();
+        if (sync)
+                synchronize_rcu();
 }
 
 static void macvlan_hash_change_addr(struct macvlan_dev *vlan,
                                         const unsigned char *addr)
 {
-        macvlan_hash_del(vlan);
+        macvlan_hash_del(vlan, true);
         /* Now that we are unhashed it is safe to change the device
          * address without confusing packet delivery.
          */
@@ -345,7 +346,7 @@ static int macvlan_stop(struct net_device *dev)
         dev_uc_del(lowerdev, dev->dev_addr);
 
 hash_del:
-        macvlan_hash_del(vlan);
+        macvlan_hash_del(vlan, !dev->dismantle);
         return 0;
 }
 
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index a134d809125b..ca333e79e10f 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1293,7 +1293,9 @@ struct net_device {
                NETREG_UNREGISTERED,     /* completed unregister todo */
                NETREG_RELEASED,         /* called free_netdev */
                NETREG_DUMMY,            /* dummy device for NAPI poll */
-        } reg_state:16;
+        } reg_state:8;
+
+        bool dismantle; /* device is going do be freed */
 
         enum {
                 RTNL_LINK_INITIALIZED,
diff --git a/net/core/dev.c b/net/core/dev.c
index 155de2094e71..d94537914a71 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5126,7 +5126,7 @@ static void rollback_registered_many(struct list_head *head)
                         list_del(&dev->unreg_list);
                         continue;
                 }
-
+                dev->dismantle = true;
                 BUG_ON(dev->reg_state != NETREG_REGISTERED);
         }