fault-injection: add CPU notifier error injection module

I used this module to test the series of modification to the cpu notifiers
code.

Example1: inject CPU offline error (-1 == -EPERM)

# modprobe cpu-notifier-error-inject cpu_down_prepare_error=-1
# echo 0 > /sys/devices/system/cpu/cpu1/online
bash: echo: write error: Operation not permitted

Example2: inject CPU online error (-2 == -ENOENT)

# modprobe cpu-notifier-error-inject cpu_up_prepare_error=-2
# echo 1 > /sys/devices/system/cpu/cpu1/online
bash: echo: write error: No such file or directory

[[e-mail]: fix Kconfig help text]
Signed-off-by: Akinobu Mita <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

lib/Kconfig.debug

···
 	Documentation on how to use the module can be found in
 	Documentation/fault-injection/provoke-crashes.txt
 
+config CPU_NOTIFIER_ERROR_INJECT
+	tristate "CPU notifier error injection module"
+	depends on HOTPLUG_CPU && DEBUG_KERNEL
+	help
+	  This option provides a kernel module that can be used to test
+	  the error handling of the cpu notifiers
+
+	  To compile this code as a module, choose M here: the module will
+	  be called cpu-notifier-error-inject.
+
+	  If unsure, say N.
+
 config FAULT_INJECTION
 	bool "Fault-injection framework"
 	depends on DEBUG_KERNEL

lib/Makefile

···
 obj-$(CONFIG_SWIOTLB) += swiotlb.o
 obj-$(CONFIG_IOMMU_HELPER) += iommu-helper.o
 obj-$(CONFIG_FAULT_INJECTION) += fault-inject.o
+obj-$(CONFIG_CPU_NOTIFIER_ERROR_INJECT) += cpu-notifier-error-inject.o
 
 lib-$(CONFIG_GENERIC_BUG) += bug.o
 

lib/cpu-notifier-error-inject.c

···
+#include <linux/kernel.h>
+#include <linux/cpu.h>
+#include <linux/module.h>
+#include <linux/notifier.h>
+
+static int priority;
+static int cpu_up_prepare_error;
+static int cpu_down_prepare_error;
+
+module_param(priority, int, 0);
+MODULE_PARM_DESC(priority, "specify cpu notifier priority");
+
+module_param(cpu_up_prepare_error, int, 0644);
+MODULE_PARM_DESC(cpu_up_prepare_error,
+		"specify error code to inject CPU_UP_PREPARE action");
+
+module_param(cpu_down_prepare_error, int, 0644);
+MODULE_PARM_DESC(cpu_down_prepare_error,
+		"specify error code to inject CPU_DOWN_PREPARE action");
+
+static int err_inject_cpu_callback(struct notifier_block *nfb,
+				unsigned long action, void *hcpu)
+{
+	int err = 0;
+
+	switch (action) {
+	case CPU_UP_PREPARE:
+	case CPU_UP_PREPARE_FROZEN:
+		err = cpu_up_prepare_error;
+		break;
+	case CPU_DOWN_PREPARE:
+	case CPU_DOWN_PREPARE_FROZEN:
+		err = cpu_down_prepare_error;
+		break;
+	}
+	if (err)
+		printk(KERN_INFO "Injecting error (%d) at cpu notifier\n", err);
+
+	return notifier_from_errno(err);
+}
+
+static struct notifier_block err_inject_cpu_notifier = {
+	.notifier_call = err_inject_cpu_callback,
+};
+
+static int err_inject_init(void)
+{
+	err_inject_cpu_notifier.priority = priority;
+
+	return register_hotcpu_notifier(&err_inject_cpu_notifier);
+}
+
+static void err_inject_exit(void)
+{
+	unregister_hotcpu_notifier(&err_inject_cpu_notifier);
+}
+
+module_init(err_inject_init);
+module_exit(err_inject_exit);
+
+MODULE_DESCRIPTION("CPU notifier error injection module");
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Akinobu Mita <[e-mail]>");