[PATCH v7 17/23] mm/ksw: add test module

[Jinchao Wang <wangjinchao600@gmail.com>]

Add a standalone test module for KStackWatch to validate functionality
in controlled scenarios.

The module exposes a simple interface via debugfs
(/sys/kernel/debug/kstackwatch/test), allowing specific test cases to
be triggered with commands such as:

  echo test0 > /sys/kernel/debug/kstackwatch/test

To ensure predictable behavior during testing, the module is built with
optimizations disabled.

Signed-off-by: Jinchao Wang <wangjinchao600@gmail.com>
---
 mm/Kconfig.debug             |  10 +++
 mm/kstackwatch/Makefile      |   6 ++
 mm/kstackwatch/kernel.c      |   5 ++
 mm/kstackwatch/kstackwatch.h |   2 +
 mm/kstackwatch/test.c        | 121 +++++++++++++++++++++++++++++++++++
 5 files changed, 144 insertions(+)
 create mode 100644 mm/kstackwatch/test.c

diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
index 24f4c4254f01..224bd561dcbb 100644
--- a/mm/Kconfig.debug
+++ b/mm/Kconfig.debug
@@ -317,3 +317,13 @@ config KSTACK_WATCH
 	  A lightweight real-time debugging tool to detect stack corruption.
 
 	  If unsure, say N.
+
+config KSTACK_WATCH_TEST
+	tristate "KStackWatch Test Module"
+	depends on KSTACK_WATCH
+	help
+	  This module provides controlled stack corruption scenarios to verify
+	  the functionality of KStackWatch. It is useful for development and
+	  validation of KStackWatch mechanism.
+
+	  If unsure, say N.
diff --git a/mm/kstackwatch/Makefile b/mm/kstackwatch/Makefile
index 84a46cb9a766..d007b8dcd1c6 100644
--- a/mm/kstackwatch/Makefile
+++ b/mm/kstackwatch/Makefile
@@ -1,2 +1,8 @@
 obj-$(CONFIG_KSTACK_WATCH)	+= kstackwatch.o
 kstackwatch-y := kernel.o stack.o watch.o
+
+obj-$(CONFIG_KSTACK_WATCH_TEST)	+= kstackwatch_test.o
+kstackwatch_test-y := test.o
+CFLAGS_test.o := -fno-inline \
+		-fno-optimize-sibling-calls \
+		-fno-pic -fno-pie -O0 -Og
diff --git a/mm/kstackwatch/kernel.c b/mm/kstackwatch/kernel.c
index 57628bace365..12b2f5ceb5d4 100644
--- a/mm/kstackwatch/kernel.c
+++ b/mm/kstackwatch/kernel.c
@@ -233,6 +233,11 @@ const struct ksw_config *ksw_get_config(void)
 	return ksw_config;
 }
 
+struct dentry *ksw_get_dbgdir(void)
+{
+	return dbgfs_dir;
+}
+
 static int __init kstackwatch_init(void)
 {
 	int ret = 0;
diff --git a/mm/kstackwatch/kstackwatch.h b/mm/kstackwatch/kstackwatch.h
index 528001534047..b7361d5d071d 100644
--- a/mm/kstackwatch/kstackwatch.h
+++ b/mm/kstackwatch/kstackwatch.h
@@ -34,6 +34,8 @@ struct ksw_config {
 
 // singleton, only modified in kernel.c
 const struct ksw_config *ksw_get_config(void);
+struct dentry *ksw_get_dbgdir(void);
+
 
 /* stack management */
 int ksw_stack_init(void);
diff --git a/mm/kstackwatch/test.c b/mm/kstackwatch/test.c
new file mode 100644
index 000000000000..80fec9cf3243
--- /dev/null
+++ b/mm/kstackwatch/test.c
@@ -0,0 +1,121 @@
+// SPDX-License-Identifier: GPL-2.0
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/debugfs.h>
+#include <linux/delay.h>
+#include <linux/kthread.h>
+#include <linux/list.h>
+#include <linux/module.h>
+#include <linux/prandom.h>
+#include <linux/printk.h>
+#include <linux/random.h>
+#include <linux/spinlock.h>
+#include <linux/string.h>
+#include <linux/uaccess.h>
+
+#include "kstackwatch.h"
+
+static struct dentry *test_file;
+
+#define BUFFER_SIZE 32
+
+static void test_watch_fire(void)
+{
+	u64 buffer[BUFFER_SIZE] = { 0 };
+
+	pr_info("entry of %s\n", __func__);
+	ksw_watch_show();
+	ksw_watch_fire();
+	pr_info("buf[0]:%lld\n", buffer[0]);
+
+	barrier_data(buffer);
+	pr_info("exit of %s\n", __func__);
+}
+
+static ssize_t test_dbgfs_write(struct file *file, const char __user *buffer,
+				size_t count, loff_t *pos)
+{
+	char cmd[256];
+	int test_num;
+
+	if (count >= sizeof(cmd))
+		return -EINVAL;
+
+	if (copy_from_user(cmd, buffer, count))
+		return -EFAULT;
+
+	cmd[count] = '\0';
+	strim(cmd);
+
+	pr_info("received command: %s\n", cmd);
+
+	if (sscanf(cmd, "test%d", &test_num) == 1) {
+		switch (test_num) {
+		case 0:
+			test_watch_fire();
+			break;
+		default:
+			pr_err("Unknown test number %d\n", test_num);
+			return -EINVAL;
+		}
+	} else {
+		pr_err("invalid command format. Use 'testN'.\n");
+		return -EINVAL;
+	}
+
+	return count;
+}
+
+static ssize_t test_dbgfs_read(struct file *file, char __user *buffer,
+			       size_t count, loff_t *ppos)
+{
+	static const char usage[] =
+		"KStackWatch Simplified Test Module\n"
+		"============ usage ===============\n"
+		"Usage:\n"
+		"echo test{i} > /sys/kernel/debug/kstackwatch/test\n"
+		" test0 - test watch fire\n";
+
+	return simple_read_from_buffer(buffer, count, ppos, usage,
+				       strlen(usage));
+}
+
+static const struct file_operations test_dbgfs_fops = {
+	.owner = THIS_MODULE,
+	.read = test_dbgfs_read,
+	.write = test_dbgfs_write,
+	.llseek = noop_llseek,
+};
+
+static int __init kstackwatch_test_init(void)
+{
+	struct dentry *ksw_dir = ksw_get_dbgdir();
+
+	if (!ksw_dir) {
+		pr_err("kstackwatch must be loaded first\n");
+		return -ENODEV;
+	}
+
+	test_file = debugfs_create_file("test", 0600, ksw_dir, NULL,
+					&test_dbgfs_fops);
+	if (!test_file) {
+		pr_err("Failed to create debugfs test file\n");
+		return -ENOMEM;
+	}
+
+	pr_info("module loaded\n");
+	return 0;
+}
+
+static void __exit kstackwatch_test_exit(void)
+{
+	debugfs_remove(test_file);
+	pr_info("module unloaded\n");
+}
+
+module_init(kstackwatch_test_init);
+module_exit(kstackwatch_test_exit);
+
+MODULE_AUTHOR("Jinchao Wang");
+MODULE_DESCRIPTION("KStackWatch Test Module");
+MODULE_LICENSE("GPL");
-- 
2.43.0