[PATCH V2] vlan:return error when real dev is enslaved

[Weiping Pan <wpan@redhat.com>]

Qinhuibin reported a kernel panic when he do some operation about vlan.
https://lkml.org/lkml/2011/11/6/218

The operation is as below:
ifconfig eth2 up
modprobe bonding
modprobe 8021q
ifconfig bond0 up
ifenslave bond0 eth2
vconfig add eth2 3300
vconfig add bond0 33
vconfig rem eth2.3300

the panic stack is as below:
[<ffffffffa002f1c9>] panic_event+0x49/0x70 [ipmi_msghandler]
[<ffffffff80378917>] notifier_call_chain+0x37/0x70
[<ffffffff80372122>] panic+0xa2/0x195
[<ffffffff80376ed8>] oops_end+0xd8/0x140
[<ffffffff8001bea7>] no_context+0xf7/0x280
[<ffffffff8001c1a5>] __bad_area_nosemaphore+0x175/0x250
[<ffffffff80376318>] page_fault+0x28/0x30
[<ffffffffa039dabd>] igb_vlan_rx_kill_vid+0x4d/0x100 [igb]
[<ffffffffa044045f>] bond_vlan_rx_kill_vid+0x9f/0x290 [bonding]
[<ffffffffa047e636>] unregister_vlan_dev+0x136/0x180 [8021q]
[<ffffffffa047ed20>] vlan_ioctl_handler+0x170/0x3f0 [8021q]
[<ffffffff802c1d3f>] sock_ioctl+0x21f/0x280
[<ffffffff800e6d7f>] vfs_ioctl+0x2f/0xb0
[<ffffffff800e726b>] do_vfs_ioctl+0x3cb/0x5a0
[<ffffffff800e74e1>] sys_ioctl+0xa1/0xb0
[<ffffffff80007388>] system_call_fastpath+0x16/0x1b
[<00007f108a2b8bd7>] 0x7f108a2b8bd7
And the nic is as below:
[root@localhost ~]# ethtool -i eth2
driver: igb
version: 3.0.6-k2
firmware-version: 1.2-1
bus-info: 0000:04:00.0
kernel version：
2.6.32.12-0.7 also happen in 2.6.32-131

For kernel 2.6.32, the reason of this bug is that when we do "vconfig add bond0 33",
adapter->vlgrp is overwritten in igb_vlan_rx_register. So when we do "vconfig rem
eth2.3300", it can't find the correct vlgrp.

And this bug is avoided by vlan cleanup patchset from Jiri Pirko
<jpirko@redhat.com>, especially commit b2cb09b1a772(igb: do vlan cleanup).

But it is not a correct operation to creat a vlan interface on eth2
when it have been enslaved by bond0, so this patch is to return error
when the real dev is already enslaved.

Changelog:
V2: use pr_err instead of pr_info

Signed-off-by: Weiping Pan <wpan@redhat.com>
---
 net/8021q/vlan.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/net/8021q/vlan.c b/net/8021q/vlan.c
index 5471628..7ce50ba 100644
--- a/net/8021q/vlan.c
+++ b/net/8021q/vlan.c
@@ -148,6 +148,11 @@ int vlan_check_real_dev(struct net_device *real_dev, u16 vlan_id)
 	const char *name = real_dev->name;
 	const struct net_device_ops *ops = real_dev->netdev_ops;
 
+	if (real_dev->flags & IFF_SLAVE) {
+		pr_err("Error, %s was already enslaved\n", name);
+		return -EOPNOTSUPP;
+	}
+
 	if (real_dev->features & NETIF_F_VLAN_CHALLENGED) {
 		pr_info("VLANs not supported on %s\n", name);
 		return -EOPNOTSUPP;
-- 
1.7.4.4