Re: [PATCH v2 03/18] mm/ksw: add /proc/kstackwatch interface

Mike Rapoport
2025-09-04T07:51:58Z

On Thu, Sep 04, 2025 at 08:21:00AM +0800, Jinchao Wang wrote:
> Provide the /proc/kstackwatch file to read or update the KSW configuration.
> Writing a valid config string starts watching; empty input stops watching.
> Invalid input stops watching and reports an error.
>
> Allocate a ksw_config struct on module init and free it on exit.
> Manage watching state with ksw_start_watching() and ksw_stop_watching().
>
> Signed-off-by: Jinchao Wang <wangjinchao600@gmail.com>
> ---
> mm/kstackwatch/kernel.c | 140 ++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 140 insertions(+)
>
> diff --git a/mm/kstackwatch/kernel.c b/mm/kstackwatch/kernel.c
> index 4a6dc49449fe..95ade95abde1 100644
> --- a/mm/kstackwatch/kernel.c
> +++ b/mm/kstackwatch/kernel.c
> @@ -1,7 +1,10 @@
> // SPDX-License-Identifier: GPL-2.0
> #include <linux/kstrtox.h>
> #include <linux/module.h>
> +#include <linux/proc_fs.h>
> +#include <linux/seq_file.h>
> #include <linux/string.h>
> +#include <linux/uaccess.h>
>
> #include "kstackwatch.h"
>
> @@ -9,6 +12,29 @@ MODULE_AUTHOR("Jinchao Wang");
> MODULE_DESCRIPTION("Kernel Stack Watch");
> MODULE_LICENSE("GPL");
>
> +struct ksw_config *ksw_config;

Does a global ksw_config imply that this is a singleton?
What happens when there are several "echo .. > /proc/kstackwatch"?
And even more interesting what happens if they are parallel?

> +bool watching_active;
> +
> +bool panic_on_catch;
> +module_param(panic_on_catch, bool, 0644);
> +MODULE_PARM_DESC(panic_on_catch,
> + "Trigger a kernel panic immediately on corruption catch");
> +
> +static int ksw_start_watching(void)
> +{
> + watching_active = true;
> +
> + pr_info("KSW: start watching %s\n", ksw_config->config_str);
> + return 0;
> +}
> +
> +static void ksw_stop_watching(void)
> +{
> + watching_active = false;
> +
> + pr_info("KSW: stop watching %s\n", ksw_config->config_str);

This module is overly verbose. Do you really need all the printks?

> +}

...

> static int __init kstackwatch_init(void)
> {
> + ksw_config = kmalloc(sizeof(*ksw_config), GFP_KERNEL);
> + if (!ksw_config)
> + return -ENOMEM;
> +
> + /* Create proc interface */
> + if (!proc_create("kstackwatch", 0644, NULL, &kstackwatch_proc_ops)) {

ksw_config must be freed here

> + pr_err("KSW: create proc kstackwatch fail");
> + return -ENOMEM;
> + }
> +
> pr_info("KSW: module loaded\n");
> pr_info("KSW: usage:\n");
> pr_info("KSW: echo 'function+ip_offset[+depth] [local_var_offset:local_var_len]' > /proc/kstackwatch\n");
> @@ -85,6 +217,14 @@ static int __init kstackwatch_init(void)
>
> static void __exit kstackwatch_exit(void)
> {
> + /* Cleanup active watching */
> + if (watching_active)
> + ksw_stop_watching();
> +
> + /* Remove proc interface */
> + remove_proc_entry("kstackwatch", NULL);
> + kfree(ksw_config);
> +
> pr_info("KSW: Module unloaded\n");
> }
>
> --
> 2.43.0
>

--
Sincerely yours,
Mike.