6.11-stable review patch. If anyone has any objections, please let me know.
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From: SeongJae Park sj@kernel.org
commit 4401e9d10ab0281a520b9f8c220f30f60b5c248f upstream.
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@kernel.org Fixes: 9294a037c015 ("mm/damon/core: implement goal-oriented feedback-driven quota auto-tuning") Signed-off-by: SeongJae Park sj@kernel.org Reported-by: Guenter Roeck linux@roeck-us.net Closes: https://lore.kernel.org/944f3d5b-9177-48e7-8ec9-7f1331a3fea3@roeck-us.net Tested-by: Guenter Roeck linux@roeck-us.net Cc: stable@vger.kernel.org [6.8.x] Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/damon/core.c | 28 +++++++++++++++++++++------- 1 file changed, 21 insertions(+), 7 deletions(-)
--- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -1450,17 +1450,31 @@ 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