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

[Rafael J. Wysocki]

On Mon, Apr 14, 2025 at 5:26 PM srinivas pandruvada
<srinivas.pandruvada@xxxxxxxxxxxxxxx> wrote:
>
> On Mon, 2025-04-14 at 17:19 +0200, Rafael J. Wysocki wrote:
> > 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@xxxxxxxxxxx>
> > >
> > > Acked-by: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>
> >
> > 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.
>
> That is correct. The below patch should work.

OK, I'll add an ACK from you to it then if you don't mind.

> >
> > The patch below should fix it.
> >
> > ===
> > From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> > 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@xxxxxxxxxxx/
> > Reported-by: Xi Ruoyao <xry111@xxxxxxxxxxx>
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> > ---
> >  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;
> >
> >               /*
> >
> >
> >
> >
>
>