Use readlocking now that assertions on vm_page_lookup() are relaxed.
Use readlocking now that assertions on vm_page_lookup() are relaxed.

Sponsored by:	EMC / Isilon storage division
Reviewed by:	alc
Tested by:	flo, pho

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase