cpufreq: powernv: Hot-plug safe the kworker thread

In the kworker_thread powernv_cpufreq_work_fn(), we can end up
sending an IPI to a cpu going offline. This is a rare corner case
which is fixed using {get/put}_online_cpus(). Along with this fix,
this patch adds changes to do oneshot cpumask_{clear/and} operation.

Suggested-by: Shreyas B Prabhu <[e-mail]>
Suggested-by: Gautham R Shenoy <[e-mail]>
Signed-off-by: Shilpasri G Bhat <[e-mail]>
Reviewed-by: Gautham R. Shenoy <[e-mail]>
Acked-by: Viresh Kumar <[e-mail]>
Signed-off-by: Rafael J. Wysocki <[e-mail]>

drivers/cpufreq/powernv-cpufreq.c

···
 #include <linux/of.h>
 #include <linux/reboot.h>
 #include <linux/slab.h>
+#include <linux/cpu.h>
 
 #include <asm/cputhreads.h>
 #include <asm/firmware.h>
···
 {
 	struct chip *chip = container_of(work, struct chip, throttle);
 	unsigned int cpu;
-	cpumask_var_t mask;
+	cpumask_t mask;
 
-	smp_call_function_any(&chip->mask,
+	get_online_cpus();
+	cpumask_and(&mask, &chip->mask, cpu_online_mask);
+	smp_call_function_any(&mask,
 			      powernv_cpufreq_throttle_check, NULL, 0);
 
 	if (!chip->restore)
-		return;
+		goto out;
 
 	chip->restore = false;
-	cpumask_copy(mask, &chip->mask);
-	for_each_cpu_and(cpu, mask, cpu_online_mask) {
-		int index, tcpu;
+	for_each_cpu(cpu, &mask) {
+		int index;
 		struct cpufreq_policy policy;
 
 		cpufreq_get_policy(&policy, cpu);
···
 					       policy.cur,
 					       CPUFREQ_RELATION_C, &index);
 		powernv_cpufreq_target_index(&policy, index);
-		for_each_cpu(tcpu, policy.cpus)
-			cpumask_clear_cpu(tcpu, mask);
+		cpumask_andnot(&mask, &mask, policy.cpus);
 	}
+out:
+	put_online_cpus();
 }
 
 static char throttle_reason[][30] = {