On Fri, 29 Sep 2006 18:29:11 -0500
linas@austin.ibm.com (Linas Vepstas) wrote:

The transmit side of the spider ethernet driver currently
places locks around some very large chunks of code. This
results in a fair amount of lock contention is some cases. 
This patch makes the locks much more fine-grained, protecting
only the cirtical sections. One lock is used to protect 
three locations: the queue head and tail pointers, and the 
queue low-watermark location.

You have spider_net_set_low_watermark() walking the tx_chain outside
tx_chain.lock.  Are you sure about that?