Re: [PATCH v5 17/23] mm/ksw: add test module

[Marco Elver <elver@google.com>]

On Wed, 24 Sept 2025 at 14:00, Jinchao Wang <wangjinchao600@gmail.com> wrote:
>
> Introduce a separate test module to validate functionality in controlled
> scenarios.
>
> The module provides a proc interface (/proc/kstackwatch_test) that allows
> triggering specific test cases via simple commands:
>
>   echo test0 > /proc/kstackwatch_test

This should not be in /proc/ - if anything, it should go into debugfs.

> Test module is built with optimizations disabled to ensure predictable
> behavior.
>
> Signed-off-by: Jinchao Wang <wangjinchao600@gmail.com>
> ---
>  mm/Kconfig.debug        |  10 ++++
>  mm/kstackwatch/Makefile |   6 ++
>  mm/kstackwatch/test.c   | 122 ++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 138 insertions(+)
>  create mode 100644 mm/kstackwatch/test.c
>
> diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
> index 89be351c0be5..291dd8a78b98 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 corrupting.
>
>           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/test.c b/mm/kstackwatch/test.c
> new file mode 100644
> index 000000000000..1ed98931cc51
> --- /dev/null
> +++ b/mm/kstackwatch/test.c
> @@ -0,0 +1,122 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +
> +#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/proc_fs.h>
> +#include <linux/random.h>
> +#include <linux/spinlock.h>
> +#include <linux/string.h>
> +#include <linux/uaccess.h>
> +
> +#include "kstackwatch.h"
> +
> +static struct proc_dir_entry *test_proc;
> +
> +#define BUFFER_SIZE 16
> +#define MAX_DEPTH 6
> +
> +struct work_node {
> +       ulong *ptr;
> +       struct completion done;
> +       struct list_head list;
> +};
> +
> +static DECLARE_COMPLETION(work_res);
> +static DEFINE_MUTEX(work_mutex);
> +static LIST_HEAD(work_list);
> +
> +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_proc_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_proc_read(struct file *file, char __user *buffer,
> +                             size_t count, loff_t *pos)
> +{
> +       static const char usage[] = "KStackWatch Simplified Test Module\n"
> +                                   "============ usage ==============\n"
> +                                   "Usage:\n"
> +                                   "echo test{i} > /proc/kstackwatch_test\n"
> +                                   " test0 - test watch fire\n";
> +
> +       return simple_read_from_buffer(buffer, count, pos, usage,
> +                                      strlen(usage));
> +}
> +
> +static const struct proc_ops test_proc_ops = {
> +       .proc_read = test_proc_read,
> +       .proc_write = test_proc_write,
> +};
> +
> +static int __init kstackwatch_test_init(void)
> +{
> +       test_proc = proc_create("kstackwatch_test", 0600, NULL, &test_proc_ops);
> +       if (!test_proc) {
> +               pr_err("Failed to create proc entry\n");
> +               return -ENOMEM;
> +       }
> +       pr_info("module loaded\n");
> +       return 0;
> +}
> +
> +static void __exit kstackwatch_test_exit(void)
> +{
> +       if (test_proc)
> +               remove_proc_entry("kstackwatch_test", NULL);
> +       pr_info("module unloaded\n");
> +}
> +
> +module_init(kstackwatch_test_init);
> +module_exit(kstackwatch_test_exit);
> +
> +MODULE_AUTHOR("Jinchao Wang");
> +MODULE_DESCRIPTION("Simple KStackWatch Test Module");
> +MODULE_LICENSE("GPL");
> --
> 2.43.0
>
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