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

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Message-ID: <aLlFDQkWBF0N7xmk@kernel.org>
Date: Thu, 4 Sep 2025 10:51:41 +0300
From: Mike Rapoport <rppt@...nel.org>
To: Jinchao Wang <wangjinchao600@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	"Naveen N . Rao" <naveen@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	"Liang, Kan" <kan.liang@...ux.intel.com>,
	David Hildenbrand <david@...hat.com>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Michal Hocko <mhocko@...e.com>, linux-perf-users@...r.kernel.org,
	linux-mm@...ck.org, linux-trace-kernel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 03/18] mm/ksw: add /proc/kstackwatch interface

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@...il.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.