Allow dynamic enabling/disabling of KStackWatch through user input of proc.
With this patch, the entire system becomes functional.

Signed-off-by: Jinchao Wang <wangjinchao600@gmail.com>
---
 mm/kstackwatch/kernel.c | 60 +++++++++++++++++++++++++++++++++++++++--
 1 file changed, 58 insertions(+), 2 deletions(-)

diff --git a/mm/kstackwatch/kernel.c b/mm/kstackwatch/kernel.c
index 898ebb2966fe..57628bace365 100644
--- a/mm/kstackwatch/kernel.c
+++ b/mm/kstackwatch/kernel.c
@@ -14,6 +14,43 @@ static struct ksw_config *ksw_config;
 static struct dentry *dbgfs_config;
 static struct dentry *dbgfs_dir;
 
+static bool watching_active;
+
+static int ksw_start_watching(void)
+{
+	int ret;
+
+	/*
+	 * Watch init will preallocate the HWBP,
+	 * so it must happen before stack init
+	 */
+	ret = ksw_watch_init();
+	if (ret) {
+		pr_err("ksw_watch_init ret: %d\n", ret);
+		return ret;
+	}
+
+	ret = ksw_stack_init();
+	if (ret) {
+		pr_err("ksw_stack_init ret: %d\n", ret);
+		ksw_watch_exit();
+		return ret;
+	}
+	watching_active = true;
+
+	pr_info("start watching: %s\n", ksw_config->user_input);
+	return 0;
+}
+
+static void ksw_stop_watching(void)
+{
+	ksw_stack_exit();
+	ksw_watch_exit();
+	watching_active = false;
+
+	pr_info("stop watching: %s\n", ksw_config->user_input);
+}
+
 struct param_map {
 	const char *name;       /* long name */
 	const char *short_name; /* short name (2 letters) */
@@ -117,8 +154,18 @@ static int ksw_parse_config(char *buf, struct ksw_config *config)
 static ssize_t ksw_dbgfs_read(struct file *file, char __user *buf, size_t count,
 			      loff_t *ppos)
 {
-	return simple_read_from_buffer(buf, count, ppos, ksw_config->user_input,
-		ksw_config->user_input ? strlen(ksw_config->user_input) : 0);
+	const char *out;
+	size_t len;
+
+	if (watching_active && ksw_config->user_input) {
+		out = ksw_config->user_input;
+		len = strlen(out);
+	} else {
+		out = "not watching\n";
+		len = strlen(out);
+	}
+
+	return simple_read_from_buffer(buf, count, ppos, out, len);
 }
 
 static ssize_t ksw_dbgfs_write(struct file *file, const char __user *buffer,
@@ -133,6 +180,9 @@ static ssize_t ksw_dbgfs_write(struct file *file, const char __user *buffer,
 	if (copy_from_user(input, buffer, count))
 		return -EFAULT;
 
+	if (watching_active)
+		ksw_stop_watching();
+
 	input[count] = '\0';
 	strim(input);
 
@@ -147,6 +197,12 @@ static ssize_t ksw_dbgfs_write(struct file *file, const char __user *buffer,
 		return ret;
 	}
 
+	ret = ksw_start_watching();
+	if (ret) {
+		pr_err("Failed to start watching with %d\n", ret);
+		return ret;
+	}
+
 	return count;
 }
 
-- 
2.43.0