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

[Jinchao Wang <wangjinchao600@gmail.com>]

On Thu, Sep 04, 2025 at 10:51:41AM +0300, Mike Rapoport wrote:
> 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?
Yes, it is.
> What happens when there are several "echo .. > /proc/kstackwatch"?
> And even more interesting what happens if they are parallel?
I did not consider this deeply enough.
I will address it properly in the next series.
Thank you for pointing it out.
> 
> > +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?
You’re right — many of these printks are for early debugging and not
needed for production. I will remove or downgrade them to pr_debug() in
the next version.

For critical paths, I’ll ensure only actionable or WARN-level messages
remain.

Appreciate the push for cleaner logging.
> 
> > +}
> 
> ...
> 
> >  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.