IB/ipoib: Fix memory leak in create child syscall

commit 4542d66b upstream.

The flow of creating a new child goes through ipoib_vlan_add
which allocates a new interface and checks the rtnl_lock.

If the lock is taken, restart_syscall will be called to restart
the system call again. In this case we are not releasing the
already allocated interface, causing a leak.

Fixes: 9baa0b03 ("IB/ipoib: Add rtnl_link_ops support")
Signed-off-by: Feras Daoud <ferasda@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/infiniband/ulp/ipoib/ipoib_vlan.c

@@ -133,13 +133,14 @@ int ipoib_vlan_add(struct net_device *pdev, unsigned short pkey)
 
 	snprintf(intf_name, sizeof intf_name, "%s.%04x",
 		 ppriv->dev->name, pkey);
-	priv = ipoib_intf_alloc(intf_name);
-	if (!priv)
-		return -ENOMEM;
 
 	if (!rtnl_trylock())
 		return restart_syscall();
 
+	priv = ipoib_intf_alloc(intf_name);
+	if (!priv)
+		return -ENOMEM;
+
 	down_write(&ppriv->vlan_rwsem);
 
 	/*