diff --git a/mm/damon/dbgfs.c b/mm/damon/dbgfs.c
index afb4e9ebc842..3181692d34d2 100644
--- a/mm/damon/dbgfs.c
+++ b/mm/damon/dbgfs.c
@@ -894,6 +894,7 @@ static ssize_t dbgfs_monitor_on_write(struct file *file,
 		for (i = 0; i < dbgfs_nr_ctxs; i++) {
 			if (damon_targets_empty(dbgfs_ctxs[i])) {
 				kfree(kbuf);
+				mutex_unlock(&damon_dbgfs_lock);
 				return -EINVAL;
 			}
 		}