[VLAN] spin lock question

[ajz at cambridgebroadband.com (Alex Zeffertt)]

Hi list,

I've been reading through the 8021q.o module source recently and
I am confused by the choice of spin lock used in the following
code:


int vlan_skb_recv(struct sk_buff *skb, struct net_device *dev,
                   struct packet_type* ptype)
{
	...
	spin_lock_bh(&vlan_group_lock);
	skb->dev = __find_vlan_dev(dev, vid);
	if (!skb->dev) {
		spin_unlock_bh(&vlan_group_lock);
	...



Now, I may have this wrong but as I understand it spin_lock_bh()
will disable softIRQs and spin_unlock_bh() will enable softIRQs (*).
But vlan_skb_recv() is called from within a softIRQ, and so it
should execute with softIRQs disabled.  Calling spin_unlock_bh()
will re-enable softIRQs, possibly having undesired consequences.

Should we be using spin_lock_irqsave/spin_lock_irqrestore instead?
I know that this is more heavy handed in that it stops *all* IRQs,
but there doesn't seem to be a spin_lock_bhsave/spin_lock_bhrestore!

Regards,

Alex


(*) This is my interpretation of what I read in
     http://www.linuxjournal.com/article/5833