panic: backing_object was somehow re-referenced during collapse!

[Peter Holm]

With GENERIC current from Jan 5 12:28 UTC I got:

panic(c0844f31,c28114a4,c28114a4,c2a098c4,c2b6794c) at panic+0xd8
vm_object_collapse(c2a098c4,c1c18000,c2bb0b6c,cfa4ac60,c076af7b)
	at vm_object_collapse+0x2ce
vm_object_deallocate(c1c18000,e,0,e,0) at
	vm_object_deallocate+0x270
vm_map_delete(c27b7bb8,0,bfc00000,c27b7bb8,0) at
	vm_map_delete+0x24f
vm_map_remove(c27b7bb8,0,bfc00000) at vm_map_remove+0x42
exit1(c2a82450,0,cfa4ad40,c07c0bf0,c2a82450) at exit1+0xb28
sysctl_kern_randompid(c2a82450,cfa4ad14,1,1,296) at
	sysctl_kern_randompid
syscall(2f,2f,2f,2804f6c0,0) at syscall+0x128

More info at http://www.holm.cc/stress/log/cons102.html 
-- 
Peter Holm