linux-kernel - Re: [PATCH 2/2] PM / arch: x86: MSR_IA32_ENERGY_PERF

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Date:   Thu, 09 May 2019 19:18:28 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Ido Schimmel <idosch@...sch.org>
Cc:     x86 <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
        Len Brown <len.brown@...el.com>,
        Linux PM <linux-pm@...r.kernel.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Laura Abbott <labbott@...oraproject.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Simon Schricker <sschricker@...e.de>,
        Borislav Petkov <bp@...e.de>, Hannes Reinecke <hare@...e.de>
Subject: Re: [PATCH 2/2] PM / arch: x86: MSR_IA32_ENERGY_PERF_BIAS sysfs interface

On Thursday, May 9, 2019 12:23:15 PM CEST Ido Schimmel wrote:
> On Thu, Mar 21, 2019 at 11:20:17PM +0100, Rafael J. Wysocki wrote:
> > +static struct attribute *intel_epb_attrs[] = {
> > +	&dev_attr_energy_perf_bias.attr,
> > +	NULL
> > +};
> > +
> > +static const struct attribute_group intel_epb_attr_group = {
> > +	.name = power_group_name,
> > +	.attrs =  intel_epb_attrs
> > +};
> > +
> >  static int intel_epb_online(unsigned int cpu)
> >  {
> > +	struct device *cpu_dev = get_cpu_device(cpu);
> > +
> >  	intel_epb_restore();
> > +	if (!cpuhp_tasks_frozen)
> > +		sysfs_merge_group(&cpu_dev->kobj, &intel_epb_attr_group);
> > +
> >  	return 0;
> >  }
> >  
> >  static int intel_epb_offline(unsigned int cpu)
> >  {
> > -	return intel_epb_save();
> > +	struct device *cpu_dev = get_cpu_device(cpu);
> > +
> > +	if (!cpuhp_tasks_frozen)
> > +		sysfs_unmerge_group(&cpu_dev->kobj, &intel_epb_attr_group);
> > +
> > +	intel_epb_save();
> > +	return 0;
> >  }
> 
> Hi,
> 
> I just booted net-next and got the following NULL pointer dereference
> [1] during boot. I believe it is caused by this patch.

I think you're right, sorry about this.

> CONFIG_PM is disabled in my config which means 'power_group_name' is
> defined as NULL. When I enable CONFIG_PM the issue is not reproduced.

So does the patch below fix it for you?

---
 arch/x86/kernel/cpu/intel_epb.c |   22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

Index: linux-pm/arch/x86/kernel/cpu/intel_epb.c
===================================================================
--- linux-pm.orig/arch/x86/kernel/cpu/intel_epb.c
+++ linux-pm/arch/x86/kernel/cpu/intel_epb.c
@@ -97,6 +97,7 @@ static void intel_epb_restore(void)
 	wrmsrl(MSR_IA32_ENERGY_PERF_BIAS, (epb & ~EPB_MASK) | val);
 }
 
+#ifdef CONFIG_PM
 static struct syscore_ops intel_epb_syscore_ops = {
 	.suspend = intel_epb_save,
 	.resume = intel_epb_restore,
@@ -193,6 +194,25 @@ static int intel_epb_offline(unsigned in
 	return 0;
 }
 
+static inline void register_intel_ebp_syscore_ops(void)
+{
+	register_syscore_ops(&intel_epb_syscore_ops);
+}
+#else /* !CONFIG_PM */
+static int intel_epb_online(unsigned int cpu)
+{
+	intel_epb_restore();
+	return 0;
+}
+
+static int intel_epb_offline(unsigned int cpu)
+{
+	return intel_epb_save();
+}
+
+static inline void register_intel_ebp_syscore_ops(void) {}
+#endif
+
 static __init int intel_epb_init(void)
 {
 	int ret;
@@ -206,7 +226,7 @@ static __init int intel_epb_init(void)
 	if (ret < 0)
 		goto err_out_online;
 
-	register_syscore_ops(&intel_epb_syscore_ops);
+	register_intel_ebp_syscore_ops();
 	return 0;
 
 err_out_online: