vlan: free percpu stats in device destructor

Madalin-Cristian reported crashs happening after a recent commit
(5a4ae5f6e7d4 "vlan: unnecessary to check if vlan_pcpu_stats is NULL")

-----------------------------------------------------------------------
root@p5040ds:~# vconfig add eth8 1
root@p5040ds:~# vconfig rem eth8.1
Unable to handle kernel paging request for data at address 0x2bc88028
Faulting instruction address: 0xc058e950
Oops: Kernel access of bad area, sig: 11 [#1]
SMP NR_CPUS=8 CoreNet Generic
Modules linked in:
CPU: 3 PID: 2167 Comm: vconfig Tainted: G        W     3.16.0-rc3-00346-g65e85bf #2
task: e7264d90 ti: e2c2c000 task.ti: e2c2c000
NIP: c058e950 LR: c058ea30 CTR: c058e900
REGS: e2c2db20 TRAP: 0300   Tainted: G        W      (3.16.0-rc3-00346-g65e85bf)
MSR: 00029002 <CE,EE,ME>  CR: 48000428  XER: 20000000
DEAR: 2bc88028 ESR: 00000000
GPR00: c047299c e2c2dbd0 e7264d90 00000000 2bc88000 00000000 ffffffff 00000000
GPR08: 0000000f 00000000 000000ff 00000000 28000422 10121928 10100000 10100000
GPR16: 10100000 00000000 c07c5968 00000000 00000000 00000000 e2c2dc48 e7838000
GPR24: c07c5bac c07c58a8 e77290cc c07b0000 00000000 c05de6c0 e7838000 e2c2dc48
NIP [c058e950] vlan_dev_get_stats64+0x50/0x170
LR [c058ea30] vlan_dev_get_stats64+0x130/0x170
Call Trace:
[e2c2dbd0] [ffffffea] 0xffffffea (unreliable)
[e2c2dc20] [c047299c] dev_get_stats+0x4c/0x140
[e2c2dc40] [c0488ca8] rtnl_fill_ifinfo+0x3d8/0x960
[e2c2dd70] [c0489f4c] rtmsg_ifinfo+0x6c/0x110
[e2c2dd90] [c04731d4] rollback_registered_many+0x344/0x3b0
[e2c2ddd0] [c047332c] rollback_registered+0x2c/0x50
[e2c2ddf0] [c0476058] unregister_netdevice_queue+0x78/0xf0
[e2c2de00] [c058d800] unregister_vlan_dev+0xc0/0x160
[e2c2de20] [c058e360] vlan_ioctl_handler+0x1c0/0x550
[e2c2de90] [c045d11c] sock_ioctl+0x28c/0x2f0
[e2c2deb0] [c010d070] do_vfs_ioctl+0x90/0x7b0
[e2c2df20] [c010d7d0] SyS_ioctl+0x40/0x80
[e2c2df40] [c000f924] ret_from_syscall+0x0/0x3c

Fix this problem by freeing percpu stats from dev->destructor() instead
of ndo_uninit()

Reported-by: Madalin-Cristian Bucur <madalin.bucur@freescale.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Tested-by: Madalin-Cristian Bucur <madalin.bucur@freescale.com>
Fixes: 5a4ae5f6e7d4 ("vlan: unnecessary to check if vlan_pcpu_stats is NULL")
Cc: Li RongQing <roy.qing.li@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/8021q/vlan_dev.c

@@ -627,8 +627,6 @@ static void vlan_dev_uninit(struct net_device *dev)
 	struct vlan_dev_priv *vlan = vlan_dev_priv(dev);
 	int i;
 
-	free_percpu(vlan->vlan_pcpu_stats);
-	vlan->vlan_pcpu_stats = NULL;
 	for (i = 0; i < ARRAY_SIZE(vlan->egress_priority_map); i++) {
 		while ((pm = vlan->egress_priority_map[i]) != NULL) {
 			vlan->egress_priority_map[i] = pm->next;
@@ -785,6 +783,15 @@ static const struct net_device_ops vlan_netdev_ops = {
 	.ndo_get_lock_subclass  = vlan_dev_get_lock_subclass,
 };
 
+static void vlan_dev_free(struct net_device *dev)
+{
+	struct vlan_dev_priv *vlan = vlan_dev_priv(dev);
+
+	free_percpu(vlan->vlan_pcpu_stats);
+	vlan->vlan_pcpu_stats = NULL;
+	free_netdev(dev);
+}
+
 void vlan_setup(struct net_device *dev)
 {
 	ether_setup(dev);
@@ -794,7 +801,7 @@ void vlan_setup(struct net_device *dev)
 	dev->tx_queue_len	= 0;
 
 	dev->netdev_ops		= &vlan_netdev_ops;
-	dev->destructor		= free_netdev;
+	dev->destructor		= vlan_dev_free;
 	dev->ethtool_ops	= &vlan_ethtool_ops;
 
 	memset(dev->broadcast, 0, ETH_ALEN);