Re: intel_pstate oopses and lockdep report with Linux v4.5-1822-g63e30271b04c

[Josh Boyer]

On Thu, Mar 17, 2016 at 10:07 AM, Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote:
> On Thursday, March 17, 2016 09:02:29 AM Josh Boyer wrote:
>> Hello,
>
> Hi,
>
>> I have an Intel Atom based NUC that is producing the following
>> backtraces on boot of Linus' tree as of last evening.  This does not
>> happen with a tree with top level commit 271ecc5253e2, but does happen
>> when using the tree mentioned in the subject with top level commit
>> 63e30271b04c.
>>
>> The first backtrace appears to be a warning because the intel_pstate
>> driver is calling wrmsrl_on_cpu when interrupts are disabled?  Not
>> sure on that one.
>>
>> The second backtrace is a lockdep report.  Both are from the same boot.
>
> OK, thanks for the report.
>
> Can you please try the patch below?
>
> I'm actually unsure if we can do that safely in general for Atom because
> of the initialization, but that's what Core does anyway.
>
> Srinivas, Philippe, why exactly do we need the wrmsrl_on_cpu() in
> atom_set_pstate()?  core_set_pstate() uses wrmsrl() and seems to be doing fine.
>
> ---
>  drivers/cpufreq/intel_pstate.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> Index: linux-pm/drivers/cpufreq/intel_pstate.c
> ===================================================================
> --- linux-pm.orig/drivers/cpufreq/intel_pstate.c
> +++ linux-pm/drivers/cpufreq/intel_pstate.c
> @@ -587,7 +587,7 @@ static void atom_set_pstate(struct cpuda
>
>         val |= vid;
>
> -       wrmsrl_on_cpu(cpudata->cpu, MSR_IA32_PERF_CTL, val);
> +       wrmsrl(MSR_IA32_PERF_CTL, val);
>  }
>
>  static int silvermont_get_scaling(void)
>

I applied this on top of commit 09fd671ccb24 and the backtrace and
lockdep report both go away.  So yes, this seems to clear up the
issue.  I tested it on a variety of different CPU types and didn't
notice anything wrong on them either.

josh