for the s2io module, a large enough rx_ring_rz will attempt to claim all memory on the system. A stupid admin <cough, cough> might naively assume rx_ring_sz could take as input the output of ethtool -g's rx ring max. The tx_fifo_sz parameter works exactly this way.

The documentation points out that:

 d. rx_ring_sz
 Size of each receive ring(in 4K blocks)
 Valid range: Limited by memory on system

but this could be a a bit more ... expected. In the vary least, maybe check if the requested rx_ring_sz exceeds current physical memory.

eg:

ahecox@intel-bensley ~ $ sudo ethtool -g eth1
Ring parameters for eth1:
Pre-set maximums:
RX:             152400
RX Mini:        0
RX Jumbo:       152400
TX:             8192
Current hardware settings:
RX:             3840
RX Mini:        0
RX Jumbo:       3840
TX:             8192

ahecox@intel-bensley ~ $ sudo rmmod s2io
ahecox@intel-bensley ~ $ modinfo s2io | grep rx
parm:           rx_ring_num:uint
parm:           rx_ring_mode:uint
parm:           rxsync_frequency:uint
parm:           rx_ring_sz:array of uint
ahecox@intel-bensley ~ $ sudo modprobe s2io rx_ring_num=1 rx_ring_sz=152400

Message from syslogd@ at Mon Mar 23 22:48:32 2009 ...
intel-bensley kernel: Unable to handle kernel paging request at 000000011fbdd290 RIP: 
Message from syslogd@ at Mon Mar 23 22:48:32 2009 ...
intel-bensley kernel:  [<ffffffff80021bee>] dma_alloc_coherent+0x2d/0x1ca