xc_tailp < xc_headp panic during boot (Was: Adding pool_cache_invalidate_local() to pool_cache(9) API)

[Geoff Wing <mason%primenet.com.au@localhost>]

Jason Thorpe <thorpej%shagadelic.org@localhost> typed:
: I'll go ahead and check it in now.

This gives me a panic during boot.
  ...
  mainbus0 (root)
  cpu0 at mainbus0 apid 0: Intel 686-class, 3005MHz, id 0x6fb
  cpu1 at mainbus0 apid 1: Intel 686-class, 3005MHz, id 0x6fb
  ioapic0 at mainbus0 apid 2: pa 0xfec00000, version 20, 24 pins
  ...
  hdafg0 at hdaudio0 vendor 0x11D4 product 0x198B nid 0x01 (firmware 
configuration)
  audio0 at hdafg0: full duplex, playback, capture, independent
  .. diagnostic assertion: xc_tailp < xc_headp .. at .../subr_xcall.c:199
  cpu0: Begin traceback
  cpu0: End traceback
  ...

Normally after audio0 would be
 "ppb1 at pci0 dev 28 function 0: Intel 82801I PCI Express Port #1 (rev. 0x02)
  pci2 at ppb1 bus 4
  pci2: memory space enabled, rd/line, wr/inv ok"

Regards,
Geoff