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SubjectRe: [PATCH 2/2] PM / arch: x86: MSR_IA32_ENERGY_PERF_BIAS sysfs interface
Date
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:


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