mm-damon-stat-detect-and-use-fresh-enabled-value.patch removed from -mm tree

The quilt patch titled
Subject: mm/damon/stat: detect and use fresh enabled value
has been removed from the -mm tree. Its filename was
mm-damon-stat-detect-and-use-fresh-enabled-value.patch

This patch was dropped because it was merged into the mm-hotfixes-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: SeongJae Park <[email protected]>
Subject: mm/damon/stat: detect and use fresh enabled value
Date: Sun, 19 Apr 2026 09:10:02 -0700

DAMON_STAT updates 'enabled' parameter value, which represents the running status of its kdamond, when the user explicitly requests start/stop of the kdamond. The kdamond can, however, be stopped even if the user explicitly requested the stop, if ctx->regions_score_histogram allocation failure at beginning of the execution of the kdamond. Hence, if the kdamond is stopped by the allocation failure, the value of the parameter can be stale.

Users could show the stale value and be confused. The problem will only rarely happen in real and common setups because the allocation is arguably too small to fail. Also, unlike the similar bugs that are now fixed in DAMON_RECLAIM and DAMON_LRU_SORT, kdamond can be restarted in this case, because DAMON_STAT force-updates the enabled parameter value for user inputs. The bug is a bug, though.

The issue stems from the fact that there are multiple events that can change the status, and following all the events is challenging. Dynamically detect and use the fresh status for the parameters when those are requested.

The issue was dicovered [1] by Sashiko.

---

 mm/damon/stat.c |   30 ++++++++++++++++++++----------
 1 file changed, 20 insertions(+), 10 deletions(-)

@@ -19,14 +19,17 @@
 static int damon_stat_enabled_store(
 		const char *val, const struct kernel_param *kp);
 
+static int damon_stat_enabled_load(char *buffer,
+		const struct kernel_param *kp);
+
 static const struct kernel_param_ops enabled_param_ops = {
 	.set = damon_stat_enabled_store,
-	.get = param_get_bool,
+	.get = damon_stat_enabled_load,
 };
 
 static bool enabled __read_mostly = IS_ENABLED(
 	CONFIG_DAMON_STAT_ENABLED_DEFAULT);
-module_param_cb(enabled, &enabled_param_ops, &enabled, 0600);
+module_param_cb(enabled, &enabled_param_ops, NULL, 0600);
 MODULE_PARM_DESC(enabled, "Enable of disable DAMON_STAT");
 
 static unsigned long estimated_memory_bandwidth __read_mostly;

@@ -273,17 +276,23 @@ static void damon_stat_stop(void)
 	damon_stat_context = NULL;
 }
 
+static bool damon_stat_enabled(void)
+{
+	if (!damon_stat_context)
+		return false;
+	return damon_is_running(damon_stat_context);
+}
+
 static int damon_stat_enabled_store(
 		const char *val, const struct kernel_param *kp)
 {
-	bool is_enabled = enabled;
 	int err;
 
 	err = kstrtobool(val, &enabled);
 	if (err)
 		return err;
 
-	if (is_enabled == enabled)
+	if (damon_stat_enabled() == enabled)
 		return 0;
 
 	if (!damon_initialized())

@@ -293,16 +302,17 @@ static int damon_stat_enabled_store(
 		 */
 		return 0;
 
-	if (enabled) {
-		err = damon_stat_start();
-		if (err)
-			enabled = false;
-		return err;
-	}
+	if (enabled)
+		return damon_stat_start();
 	damon_stat_stop();
 	return 0;
 }
 
+static int damon_stat_enabled_load(char *buffer, const struct kernel_param *kp)
+{
+	return sprintf(buffer, "%c\n", damon_stat_enabled() ? 'Y' : 'N');
+}
+
 static int __init damon_stat_init(void)
 {
 	int err = 0;

_

Patches currently in -mm which might be from [email protected] are

mm-damon-sysfs-schemes-call-missing-mem_cgroup_iter_break.patch mm-damon-fix-damos_stat-tracepoint-format-for-sz_applied.patch docs-mm-damon-maintainer-profile-add-ai-review-usage-guideline.patch