[PATCH v4 06/21] mm/ksw: add singleton /proc/kstackwatch interface

Jinchao Wang
2025-09-12T10:12:27Z

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.

ksw_get_config() exposes the configuration pointer as const.

Signed-off-by: Jinchao Wang <wangjinchao600@gmail.com>
---
mm/kstackwatch/kernel.c | 75 +++++++++++++++++++++++++++++++++++-
mm/kstackwatch/kstackwatch.h | 3 ++
2 files changed, 77 insertions(+), 1 deletion(-)

diff --git a/mm/kstackwatch/kernel.c b/mm/kstackwatch/kernel.c
index 1502795e02af..8e1dca45003e 100644
--- a/mm/kstackwatch/kernel.c
+++ b/mm/kstackwatch/kernel.c
@@ -3,7 +3,10 @@

#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"

@@ -12,6 +15,7 @@ MODULE_DESCRIPTION("Kernel Stack Watch");
MODULE_LICENSE("GPL");

static struct ksw_config *ksw_config;
+static atomic_t config_file_busy = ATOMIC_INIT(0);

/*
* Format of the configuration string:
@@ -23,7 +27,7 @@ static struct ksw_config *ksw_config;
* - local_var_offset : offset from the stack pointer at function+ip_offset
* - local_var_len : length of the local variable(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 *func_part, *local_var_part = NULL;
char *token;
@@ -92,18 +96,87 @@ static int __maybe_unused ksw_parse_config(char *buf, struct ksw_config *config)
return -EINVAL;
}

+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->config_str);
+ 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);

pr_info("module unloaded\n");
diff --git a/mm/kstackwatch/kstackwatch.h b/mm/kstackwatch/kstackwatch.h
index 7c595c5c24d1..277b192f80fa 100644
--- a/mm/kstackwatch/kstackwatch.h
+++ b/mm/kstackwatch/kstackwatch.h
@@ -35,4 +35,7 @@ struct ksw_config {
char config_str[MAX_CONFIG_STR_LEN];
};

+// singleton, only modified in kernel.c
+const struct ksw_config *ksw_get_config(void);
+
#endif /* _KSTACKWATCH_H */
--
2.43.0