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

From: Philippe Longepe
Date: Thu Mar 17 2016 - 10:33:14 EST


The wmsrl is supposed to write on the MSR corresponding to the cpu that is executing it.

However, it seems that the following commit done by Joe Konno already fixed this bug on BYT.


Now, we need to figure out why the wmsrl is not executed on the current cpu!



On 17/03/2016 15:07, Rafael J. Wysocki wrote:
On Thursday, March 17, 2016 09:02:29 AM Josh Boyer wrote:

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

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)