Re: [PATCH] cpufreq: intel_pstate: Use raw_smp_processor_id() in hwp_get_cpu_scaling()

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

On Sunday, April 13, 2025 4:44:56 PM CEST srinivas pandruvada wrote:
> On Sat, 2025-04-12 at 18:34 +0800, Xi Ruoyao wrote:
> > Use raw_smp_processor_id() instead of plain smp_processor_id() in
> > hwp_get_cpu_scaling(), otherwise we get some errors on a Lenovo
> > Thinkpad
> > T14P Gen 2:
> > 
> >     BUG: using smp_processor_id() in preemptible [00000000] code:
> > swapper/0/1
> >     caller is hwp_get_cpu_scaling+0x7f/0xc0
> > 
> > Fixes: b52aaeeadfac ("cpufreq: intel_pstate: Avoid SMP calls to get
> > cpu-type")
> > Signed-off-by: Xi Ruoyao <xry111@xry111.site>
>
> Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>

It's still broken after this patch though because the function should
use the cpu_data() of the target CPU and not of the CPU running the code.

The patch below should fix it.

===
From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Subject: [PATCH v1] cpufreq: intel_pstate: Fix hwp_get_cpu_scaling()

Commit b52aaeeadfac ("cpufreq: intel_pstate: Avoid SMP calls to get
cpu-type") introduced two issues into hwp_get_cpu_scaling().  First,
it made that function use the CPU type of the CPU running the code
even though the target CPU is passed as the argument to it and second,
it used smp_processor_id() for that even though hwp_get_cpu_scaling()
runs in preemptible context.

Fix both of these problems by simply passing "cpu" to cpu_data().

Fixes: b52aaeeadfac ("cpufreq: intel_pstate: Avoid SMP calls to get cpu-type")
Link: https://lore.kernel.org/linux-pm/20250412103434.5321-1-xry111@xry111.site/
Reported-by: Xi Ruoyao <xry111@xry111.site>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
 drivers/cpufreq/intel_pstate.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -2336,7 +2336,7 @@
 static int hwp_get_cpu_scaling(int cpu)
 {
 	if (hybrid_scaling_factor) {
-		struct cpuinfo_x86 *c = &cpu_data(smp_processor_id());
+		struct cpuinfo_x86 *c = &cpu_data(cpu);
 		u8 cpu_type = c->topo.intel_type;
 
 		/*