linux-kernel - Re: [PATCH] cpufreq: intel_pstate: Use raw_smp_processor_id() in hwp_get_cpu

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Message-ID: <5dd2e5c6abb39dfafee91247cd8473ec643280ac.camel@linux.intel.com>
Date: Mon, 14 Apr 2025 08:26:18 -0700
From: srinivas pandruvada <srinivas.pandruvada@...ux.intel.com>
To: "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc: Xi Ruoyao <xry111@...111.site>, "Rafael J. Wysocki" <rafael@...nel.org>,
  Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>, Dave Hansen
 <dave.hansen@...ux.intel.com>,  linux-pm@...r.kernel.org,
 linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] cpufreq: intel_pstate: Use raw_smp_processor_id() in
 hwp_get_cpu_scaling()

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@...111.site>
> > 
> > Acked-by: Srinivas Pandruvada <srinivas.pandruvada@...ux.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.

That is correct. The below patch should work.

Thanks,
Srinivas

> 
> The patch below should fix it.
> 
> ===
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.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@...111.site>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.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;
>  
>  		/*
> 
> 
> 
>