Created attachment 150294 [details]
This is a bug that may have been present in earlier versions of FreeBSD, but since upgrading to FreeBSD 10.1-RELEASE I can regularly reproduce.
The environment is a custom live CD, configured with a preloaded ufs.gz base bootstrap image that mounts a ufs.uzip file as the new root, creates a malloc-based virtual disk, and overlays it over the existing RO ufs.uzip image via unionfs.
Fatal trap 12: page fault while in kernel mode
cpuid = 0; apic id = 00
fault virtual address= 0x0
fault code= supervisor read, page not present
current process= 2626 (rmdir)
[ thread pid 2626 tid 100065 ]
Stopped at strlen+0xd: movl 0(%ecx),%eax
tracing pid 2626 tid 100065 td 0xc8dfe620
--- syscall (137, FreeBSD ELF32, sys_rmdir)
Created attachment 150295 [details]
Caused by kernel module mismatch.