Re: [RFC PATCH v5 8/8] Docs/ABI/damon: update for quota goal metric complement sysfs file

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] mm: integer overflow in damos_set_psi_current_val() on 32-bit
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commit 5d7327c0afcb5fe144677a675b1eea685917f61e
Author: SJ Park <sj@kernel.org>
Docs/ABI/damon: update for quota goal metric complement sysfs file

This commit introduces a complement flag for the quota auto-tuning goal metric
and updates the sysfs ABI documentation to reflect this addition. It also
modifies the core DAMON tuning logic to support the complement calculation.

> diff --git a/mm/damon/core.c b/mm/damon/core.c
> index 733025b367457..86f13411b91fa 100644
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c

[ ... ]

> @@ -2960,10 +2962,18 @@ static void damos_set_psi_current_val(u64 now_psi_total,
>  		struct damos_quota_goal *goal, struct damos *s)
>  {
>  	u64 last_psi_total = goal->last_psi_total;
> +	unsigned long val;
>  
>  	goal->last_psi_total = now_psi_total;
>  	if (last_psi_total != U64_MAX) {
> -		goal->current_value = now_psi_total - last_psi_total;
> +		val = now_psi_total - last_psi_total;
> +		if (goal->complement) {
> +			if (val < s->quota.reset_interval * 1000)
> +				val = s->quota.reset_interval * 1000 - val;

[Severity: Medium]
Could this multiplication in mm/damon/core.c:damos_set_psi_current_val()
overflow on 32-bit systems?  If reset_interval is configured to a value
greater than 4,294,967 (about 71 minutes) via sysfs,
s->quota.reset_interval * 1000 will exceed the maximum value of a 32-bit
unsigned long.

This could cause the complement calculation to yield corrupted values or
premature zeros, breaking the auto-tuning logic.

> +			else
> +				val = 0;
> +		}
> +		goal->current_value = val;
>  		return;
>  	}
>  	/* uninitialized last_psi_total; make no effect this round */

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260928093342.16584-1-sj@kernel.org?part=8