torture: Replace cpu_up/down() with add/remove_cpu()

The core device API performs extra housekeeping bits that are missing
from directly calling cpu_up/down().

See commit a6717c01dd ("powerpc/rtas: use device model APIs and
serialization during LPM") for an example description of what might go
wrong.

This also prepares to make cpu_up/down() a private interface of the CPU
subsystem.

Signed-off-by: Qais Yousef <qais.yousef@arm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: "Paul E. McKenney" <paulmck@kernel.org>
Link: https://lkml.kernel.org/r/20200323135110.30522-16-qais.yousef@arm.com

kernel/torture.c

@@ -97,7 +97,7 @@ bool torture_offline(int cpu, long *n_offl_attempts, long *n_offl_successes,
 			 torture_type, cpu);
 	starttime = jiffies;
 	(*n_offl_attempts)++;
-	ret = cpu_down(cpu);
+	ret = remove_cpu(cpu);
 	if (ret) {
 		if (verbose)
 			pr_alert("%s" TORTURE_FLAG
@@ -148,7 +148,7 @@ bool torture_online(int cpu, long *n_onl_attempts, long *n_onl_successes,
 			 torture_type, cpu);
 	starttime = jiffies;
 	(*n_onl_attempts)++;
-	ret = cpu_up(cpu);
+	ret = add_cpu(cpu);
 	if (ret) {
 		if (verbose)
 			pr_alert("%s" TORTURE_FLAG
@@ -192,17 +192,18 @@ torture_onoff(void *arg)
 	for_each_online_cpu(cpu)
 		maxcpu = cpu;
 	WARN_ON(maxcpu < 0);
-	if (!IS_MODULE(CONFIG_TORTURE_TEST))
+	if (!IS_MODULE(CONFIG_TORTURE_TEST)) {
 		for_each_possible_cpu(cpu) {
 			if (cpu_online(cpu))
 				continue;
-			ret = cpu_up(cpu);
+			ret = add_cpu(cpu);
 			if (ret && verbose) {
 				pr_alert("%s" TORTURE_FLAG
 					 "%s: Initial online %d: errno %d\n",
 					 __func__, torture_type, cpu, ret);
 			}
 		}
+	}
 
 	if (maxcpu == 0) {
 		VERBOSE_TOROUT_STRING("Only one CPU, so CPU-hotplug testing is disabled");