hwmon: (fam15h_power) Disable preemption when reading registers

We need to read a bunch of registers on each compute unit and possibly
on the current CPU too. Disable preemption around it. Otherwise, you
get:

BUG: using smp_processor_id() in preemptible [00000000] code: systemd-udevd/327
caller is read_registers+0x6a/0x110 [fam15h_power]
CPU: 3 PID: 327 Comm: systemd-udevd Not tainted 4.7.0-rc1+ #4
Hardware name: HP HP EliteBook 745 G3/807E, BIOS N73 Ver. 01.08 01/28/2016
...

Suggested-by: Thomas Gleixner <[e-mail]>
Signed-off-by: Borislav Petkov <[e-mail]>
Cc: Rui Huang <[e-mail]>
Cc: Sherry Hurwitz <[e-mail]>
Cc: Guenter Roeck <[e-mail]>
Acked-by: Huang Rui <[e-mail]>
Tested-by: Huang Rui <[e-mail]>
Fixes: fa7943449943 ("hwmon: (fam15h_power) Add compute unit accumulated power")
Signed-off-by: Guenter Roeck <[e-mail]>

drivers/hwmon/fam15h_power.c

···
  */
 static int read_registers(struct fam15h_power_data *data)
 {
-	int this_cpu, ret, cpu;
 	int core, this_core;
 	cpumask_var_t mask;
+	int ret, cpu;
 
 	ret = zalloc_cpumask_var(&mask, GFP_KERNEL);
 	if (!ret)
···
 	memset(data->cu_on, 0, sizeof(int) * MAX_CUS);
 
 	get_online_cpus();
-	this_cpu = smp_processor_id();
 
 	/*
 	 * Choose the first online core of each compute unit, and then
···
 		cpumask_set_cpu(cpumask_any(topology_sibling_cpumask(cpu)), mask);
 	}
 
-	if (cpumask_test_cpu(this_cpu, mask))
-		do_read_registers_on_cu(data);
+	on_each_cpu_mask(mask, do_read_registers_on_cu, data, true);
 
-	smp_call_function_many(mask, do_read_registers_on_cu, data, true);
 	put_online_cpus();
-
 	free_cpumask_var(mask);
 
 	return 0;