mm-damon-core-avoid-overflow-in-damon_feed_loop_next_input.patch removed from -mm tree

The quilt patch titled
Subject: mm/damon/core: avoid overflow in damon_feed_loop_next_input()
has been removed from the -mm tree. Its filename was
mm-damon-core-avoid-overflow-in-damon_feed_loop_next_input.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/core: avoid overflow in damon_feed_loop_next_input()
Date: Thu, 31 Oct 2024 09:12:03 -0700

damon_feed_loop_next_input() is inefficient and fragile to overflows. Specifically, 'score_goal_diff_bp' calculation can overflow when 'score' is high. The calculation is actually unnecessary at all because 'goal' is a constant of value 10,000. Calculation of 'compensation' is again fragile to overflow. Final calculation of return value for under-achiving case is again fragile to overflow when the current score is under-achieving the target.

Add two corner cases handling at the beginning of the function to make the body easier to read, and rewrite the body of the function to avoid overflows and the unnecessary bp value calcuation.

---

 mm/damon/core.c |   28 +++++++++++++++++++++-------
 1 file changed, 21 insertions(+), 7 deletions(-)

@@ -1456,17 +1456,31 @@ static unsigned long damon_feed_loop_nex
 		unsigned long score)
 {
 	const unsigned long goal = 10000;
-	unsigned long score_goal_diff = max(goal, score) - min(goal, score);
-	unsigned long score_goal_diff_bp = score_goal_diff * 10000 / goal;
-	unsigned long compensation = last_input * score_goal_diff_bp / 10000;
 	/* Set minimum input as 10000 to avoid compensation be zero */
 	const unsigned long min_input = 10000;
+	unsigned long score_goal_diff, compensation;
+	bool over_achieving = score > goal;
 
-	if (goal > score)
+	if (score == goal)
+		return last_input;
+	if (score >= goal * 2)
+		return min_input;
+
+	if (over_achieving)
+		score_goal_diff = score - goal;
+	else
+		score_goal_diff = goal - score;
+
+	if (last_input < ULONG_MAX / score_goal_diff)
+		compensation = last_input * score_goal_diff / goal;
+	else
+		compensation = last_input / goal * score_goal_diff;
+
+	if (over_achieving)
+		return max(last_input - compensation, min_input);
+	if (last_input < ULONG_MAX - compensation)
 		return last_input + compensation;
-	if (last_input > compensation + min_input)
-		return last_input - compensation;
-	return min_input;
+	return ULONG_MAX;
 }
 
 #ifdef CONFIG_PSI

_

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

selftests-damon-huge_count_read_write-remove-unnecessary-debugging-message.patch selftests-damon-_debugfs_common-hide-expected-error-message-from-test_write_result.patch selftests-damon-debugfs_duplicate_context_creation-hide-errors-from-expected-file-write-failures.patch mm-damon-kconfig-update-dbgfs_kunit-prompt-copy-for-sysfs_kunit.patch mm-damon-tests-dbgfs-kunit-fix-the-header-double-inclusion-guarding-ifdef-comment.patch docs-mm-damon-recommend-academic-papers-to-read-and-or-cite.patch maintainers-memory-management-add-document-files-for-mm.patch