kfree_skb query

I'm writing a driver that provides an ethernet like interface to a WAN link. The device DMA's the data from me, then tells me when it's finished. At that point I free the skb. However I get the following warning

kernel: Warning: kfree_skb on hard IRQ d092c301

What is bad about calling kfree_skb from within a hard IRQ? I'm afraid looking at the code that spat out the error message didn't help me, and since it's only a warning I'm assuming it's not fatal, but shouldn't be done for some reason.

Thanks.

Bill

Bill Leckey - Senior Software Design Engineer
TPG Research and Development
Ph: +61 2 62851711
Fax: +61 2 62853939