# DF-2392 - machdep.acpi_timer_freq=0 divide-by-zero panic

## Reproduce (STOCK kernel, root)
  sysctl -w machdep.acpi_timer_freq=0
-> Fatal trap 18: integer divide fault while in kernel mode
   Stopped at cputimer_set_frequency+0x10: divq %rsi,%eax

The only validation in acpi_timer_sysctl_freq (acpi_timer.c:310-311)
checks the CURRENT acpi_cputimer.freq, never the user-supplied new value.

## Fixed kernel (fix.diff: reject freq==0 with EINVAL)
  sysctl machdep.acpi_timer_freq=0 -> Invalid argument (no panic)