The patch titled
Subject: mm/damon/core: avoid overflow in damon_feed_loop_next_input()
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-damon-core-avoid-overflow-in-damon_feed_loop_next_input.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-damon-core-avoid-overflow-in-damon_feed_loop_next_input.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: SeongJae Park <sj@xxxxxxxxxx>
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.
Link: https://lkml.kernel.org/r/20241031161203.47751-1-sj@xxxxxxxxxx
Fixes: 9294a037c015 ("mm/damon/core: implement goal-oriented feedback-driven quota auto-tuning")
Signed-off-by: SeongJae Park <sj@xxxxxxxxxx>
Reported-by: Guenter Roeck <linux@xxxxxxxxxxxx>
Closes: https://lore.kernel.org/944f3d5b-9177-48e7-8ec9-7f1331a3fea3@xxxxxxxxxxxx
Tested-by: Guenter Roeck <linux@xxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [6.8.x]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/damon/core.c | 28 +++++++++++++++++++++-------
1 file changed, 21 insertions(+), 7 deletions(-)
--- a/mm/damon/core.c~mm-damon-core-avoid-overflow-in-damon_feed_loop_next_input
+++ a/mm/damon/core.c
@@ -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 sj@xxxxxxxxxx are
mm-damon-core-handle-zero-aggregationops_update-intervals.patch
mm-damon-core-handle-zero-schemes-apply-interval.patch
mm-damon-core-avoid-overflow-in-damon_feed_loop_next_input.patch
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
