selftests/cpu-hotplug: Reserve one cpu online at least

Considering that we can not offline all cpus in any cases,
we need to reserve one cpu online when the test offline all
hotpluggable online cpus, otherwise the test will fail forever.

Fixes: d89dffa976bc ("fault-injection: add selftests for cpu and memory hotplug")

Signed-off-by: Zhao Gongyi <[e-mail]>
Signed-off-by: Shuah Khan <[e-mail]>

tools/testing/selftests/cpu-hotplug/cpu-on-off-test.sh

···
 	fi
 }
 
+online_all_hot_pluggable_cpus()
+{
+	for cpu in `hotplaggable_offline_cpus`; do
+		online_cpu_expect_success $cpu
+	done
+}
+
+offline_all_hot_pluggable_cpus()
+{
+	local reserve_cpu=$online_max
+	for cpu in `hotpluggable_online_cpus`; do
+		# Reserve one cpu oneline at least.
+		if [ $cpu -eq $reserve_cpu ];then
+			continue
+		fi
+		offline_cpu_expect_success $cpu
+	done
+}
+
 allcpus=0
 online_cpus=0
 online_max=0
···
 	echo -e "\t online all offline cpus"
 fi
 
-#
-# Online all hot-pluggable CPUs
-#
-for cpu in `hotplaggable_offline_cpus`; do
-	online_cpu_expect_success $cpu
-done
+online_all_hot_pluggable_cpus
 
-#
-# Offline all hot-pluggable CPUs
-#
-for cpu in `hotpluggable_online_cpus`; do
-	offline_cpu_expect_success $cpu
-done
+offline_all_hot_pluggable_cpus
 
-#
-# Online all hot-pluggable CPUs again
-#
-for cpu in `hotplaggable_offline_cpus`; do
-	online_cpu_expect_success $cpu
-done
+online_all_hot_pluggable_cpus
 
 exit $retval