[PATCH v8 21/27] mm/ksw: add test module

Jinchao Wang
2025-11-10T16:38:15Z

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>

show addr of buf and watch_addr of test case
---
include/linux/kstackwatch.h | 2 +
mm/kstackwatch/Kconfig | 10 +++
mm/kstackwatch/Makefile | 6 ++
mm/kstackwatch/kernel.c | 5 ++
mm/kstackwatch/test.c | 121 ++++++++++++++++++++++++++++++++++++
5 files changed, 144 insertions(+)
create mode 100644 mm/kstackwatch/test.c

diff --git a/include/linux/kstackwatch.h b/include/linux/kstackwatch.h
index 6daded932ba6..7711efe85240 100644
--- a/include/linux/kstackwatch.h
+++ b/include/linux/kstackwatch.h
@@ -40,6 +40,8 @@ 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/Kconfig b/mm/kstackwatch/Kconfig
index 3c9385a15c33..343b492ddbd3 100644
--- a/mm/kstackwatch/Kconfig
+++ b/mm/kstackwatch/Kconfig
@@ -22,3 +22,13 @@ config KSTACKWATCH_PROFILING
stopping. Useful for performance tuning, not for production use.

If unsure, say N.
+
+config KSTACKWATCH_TEST
+ tristate "KStackWatch Test Module"
+ depends on KSTACKWATCH
+ 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 c99c621eac02..a2c7cd647f69 100644
--- a/mm/kstackwatch/Makefile
+++ b/mm/kstackwatch/Makefile
@@ -1,2 +1,8 @@
obj-$(CONFIG_KSTACKWATCH) += kstackwatch.o
kstackwatch-y := kernel.o stack.o watch.o
+
+obj-$(CONFIG_KSTACKWATCH_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 a0e676e60692..b25cf6830b15 100644
--- a/mm/kstackwatch/kernel.c
+++ b/mm/kstackwatch/kernel.c
@@ -235,6 +235,11 @@ 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/test.c b/mm/kstackwatch/test.c
new file mode 100644
index 000000000000..2969564b1a00
--- /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/kstackwatch.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>
+
+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();
+ pr_info("buf: 0x%px\n", buffer);
+
+ ksw_watch_fire();
+
+ 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