panic with em(4) in current

Something with the latest e1000 update in current causes a panic during
attach on my laptop.  Rolling sys/dev/e1000 back to the previous version
fixes the problem.  Here's the hand transcribed panic:

panic: mtx_lock() of spin mutex &dev_spec->swflag_mutex _at_ ../../../dev/e1000/e1000_ich8lan.c:651

The back trace places me at: e1000_acquire_swflag_ich8lan()+0x30

The device in question is in my lenovo x61s laptop and the pciconf
output is:

em0_at_pci0:0:25:0:        class=0x020000 card=0x20de17aa chip=0x10498086 rev=0x03 hdr=0x00
    vendor     = 'Intel Corporation'
    device     = 'Gigabit Network Connection Interface Controller (82566MM NIC)'
    class      = network
    subclass   = ethernet

Thanks,
Brooks