Re: [PATCH v5 06/23] mm/ksw: add singleton /proc/kstackwatch interface

[Jinchao Wang <wangjinchao600@gmail.com>]

On Wed, Sep 24, 2025 at 10:49:35PM +0200, Marco Elver wrote:
> On Wed, 24 Sept 2025 at 13:51, Jinchao Wang <wangjinchao600@gmail.com> wrote:
> >
> > Provide the /proc/kstackwatch file to read or update the configuration.
> > Only a single process can open this file at a time, enforced using atomic
> > config_file_busy, to prevent concurrent access.
> 
> Why is this in /proc and not debugfs?
Thanks, will fix in next version.
> 
> > ksw_get_config() exposes the configuration pointer as const.
> >
> > Signed-off-by: Jinchao Wang <wangjinchao600@gmail.com>
> > ---
> >  mm/kstackwatch/kernel.c      | 77 +++++++++++++++++++++++++++++++++++-
> >  mm/kstackwatch/kstackwatch.h |  3 ++
> >  2 files changed, 79 insertions(+), 1 deletion(-)
> >
> > diff --git a/mm/kstackwatch/kernel.c b/mm/kstackwatch/kernel.c
> > index 3b7009033dd4..4a06ddadd9c7 100644
> > --- a/mm/kstackwatch/kernel.c
> > +++ b/mm/kstackwatch/kernel.c
> > @@ -3,11 +3,15 @@
> >
> >  #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"
> >
> >  static struct ksw_config *ksw_config;
> > +static atomic_t config_file_busy = ATOMIC_INIT(0);
> >
> >  struct param_map {
> >         const char *name;       /* long name */
> > @@ -74,7 +78,7 @@ static int ksw_parse_param(struct ksw_config *config, const char *key,
> >   * - sp_offset  |so (u16) : offset from stack pointer at func_offset
> >   * - watch_len  |wl (u16) : watch length (1,2,4,8)
> >   */
> > -static int __maybe_unused ksw_parse_config(char *buf, struct ksw_config *config)
> > +static int ksw_parse_config(char *buf, struct ksw_config *config)
> >  {
> >         char *part, *key, *val;
> >         int ret;
> > @@ -109,18 +113,89 @@ static int __maybe_unused ksw_parse_config(char *buf, struct ksw_config *config)
> >         return 0;
> >  }
> >
> > +static ssize_t kstackwatch_proc_write(struct file *file,
> > +                                     const char __user *buffer, size_t count,
> > +                                     loff_t *pos)
> > +{
> > +       char input[MAX_CONFIG_STR_LEN];
> > +       int ret;
> > +
> > +       if (count == 0 || count >= sizeof(input))
> > +               return -EINVAL;
> > +
> > +       if (copy_from_user(input, buffer, count))
> > +               return -EFAULT;
> > +
> > +       input[count] = '\0';
> > +       strim(input);
> > +
> > +       if (!strlen(input)) {
> > +               pr_info("config cleared\n");
> > +               return count;
> > +       }
> > +
> > +       ret = ksw_parse_config(input, ksw_config);
> > +       if (ret) {
> > +               pr_err("Failed to parse config %d\n", ret);
> > +               return ret;
> > +       }
> > +
> > +       return count;
> > +}
> > +
> > +static int kstackwatch_proc_show(struct seq_file *m, void *v)
> > +{
> > +       seq_printf(m, "%s\n", ksw_config->user_input);
> > +       return 0;
> > +}
> > +
> > +static int kstackwatch_proc_open(struct inode *inode, struct file *file)
> > +{
> > +       if (atomic_cmpxchg(&config_file_busy, 0, 1))
> > +               return -EBUSY;
> > +
> > +       return single_open(file, kstackwatch_proc_show, NULL);
> > +}
> > +
> > +static int kstackwatch_proc_release(struct inode *inode, struct file *file)
> > +{
> > +       atomic_set(&config_file_busy, 0);
> > +       return single_release(inode, file);
> > +}
> > +
> > +static const struct proc_ops kstackwatch_proc_ops = {
> > +       .proc_open = kstackwatch_proc_open,
> > +       .proc_read = seq_read,
> > +       .proc_write = kstackwatch_proc_write,
> > +       .proc_lseek = seq_lseek,
> > +       .proc_release = kstackwatch_proc_release,
> > +};
> > +
> > +const struct ksw_config *ksw_get_config(void)
> > +{
> > +       return ksw_config;
> > +}
> >  static int __init kstackwatch_init(void)
> >  {
> >         ksw_config = kzalloc(sizeof(*ksw_config), GFP_KERNEL);
> >         if (!ksw_config)
> >                 return -ENOMEM;
> >
> > +       if (!proc_create("kstackwatch", 0600, NULL, &kstackwatch_proc_ops)) {
> > +               pr_err("create proc kstackwatch fail");
> > +               kfree(ksw_config);
> > +               return -ENOMEM;
> > +       }
> > +
> >         pr_info("module loaded\n");
> >         return 0;
> >  }
> >
> >  static void __exit kstackwatch_exit(void)
> >  {
> > +       remove_proc_entry("kstackwatch", NULL);
> > +       kfree(ksw_config->func_name);
> > +       kfree(ksw_config->user_input);
> >         kfree(ksw_config);
> >
> >         pr_info("module unloaded\n");
> > diff --git a/mm/kstackwatch/kstackwatch.h b/mm/kstackwatch/kstackwatch.h
> > index a7bad207f863..983125d5cf18 100644
> > --- a/mm/kstackwatch/kstackwatch.h
> > +++ b/mm/kstackwatch/kstackwatch.h
> > @@ -29,4 +29,7 @@ struct ksw_config {
> >         char *user_input;
> >  };
> >
> > +// singleton, only modified in kernel.c
> > +const struct ksw_config *ksw_get_config(void);
> > +
> >  #endif /* _KSTACKWATCH_H */
> > --
> > 2.43.0
> >
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-- 
Jinchao