kern/108581: [sysctl] sysctl: hw.acpi.cpu.cx_lowest: Invalid argument

[Nate Lawson]

Stephane E. Potvin wrote:
> Andriy Gapon wrote:
>> on 26/03/2009 17:10 Bruce Cran said the following:
>>> On Thu, 26 Mar 2009 17:04:19 +0200
>>> Andriy Gapon <avg at icyb.net.ua> wrote:
>>>
>>>> on 26/03/2009 16:41 Bruce Cran said the following:
>>>>> I added lots of printfs to acpi_cpu.c and found that it's occuring
>>>>> in acpi_cpu_startup; initializing it to 3 in that function (which I
>>>>> wrongly assumed was the lowest Cx state supported in ACPI) fixed
>>>>> the problem on my Athlon XP PC because the generic cx handling code
>>>>> then lowered cpu_cx_count to 1 based on the fact that
>>>>> sc->cpu_cx_count was also 1.
>>>>>
>>>> Ok, yes, the real issue is in acpi_cpu_generic_cx_probe, namely in
>>>> early exits from it. So,  sc->cpu_cx_count is always set to at least
>>>> 1, but if we exit via one of the returns before the end of function,
>>>> then global cpu_cx_count is never updated.
>>>>
>>> Exactly:
>>>
>>> acpi: acpi_cpu_startup: initializing cpu_cx_count to 0
>>> acpi_cpu_generic_cx_probe
>>> if sc->cpu_p_blk_len < 5  [sc->cpu_p_blk_len = 0]
>>> acpi: acpi_cpu_startup: cpu 0,cpu_cx_count = 0,sc->cpu_cx_count = 1
>>>
>>> So we're hitting an early exit in acpi_cpu_generic_cx_probe.
>>>
>> John, what would be a better fix - initialize the global variable to 1 or use goto
>> in acpi_cpu_generic_cx_probe?
>> I think the latter is more consistent and obvious, the former is simpler and
>> safer, though.
>>
> 
> Your right, it seems that I need to order some more pointy hats. There
> should have been a goto there to jump at the end in order to initialize
> the global cpu_cx_count. The following patch should fix your issue.
> John, is this ok with you?

John's patch does the same thing without a goto (see message
<200903261129.50419.jhb at freebsd.org>)

-- 
Nate