Re: [PATCH 1/8] mm/damon/core: introduce damos_quota_goal->complement

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] damon: integer overflow in psi complement calculation on 32-bit
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commit 194cde60eb24e43a85afddadebba1bd09c82f1e0
Author: SJ Park <sj@kernel.org>

mm/damon/core: introduce damos_quota_goal->complement

This commit introduces the complement flag to the damos_quota_goal structure
to specify whether to use a complemented value of the goal target metric. It
also implements the core logic to handle this flag during quota goal commit
and metric retrieval.

> diff --git a/mm/damon/core.c b/mm/damon/core.c
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c
[ ... ]
> @@ -2960,10 +2961,18 @@ 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: Low]
Does this calculation overflow on 32-bit systems?

On 32-bit architectures, s->quota.reset_interval is a 32-bit unsigned long.
Multiplying it by the integer literal 1000 will overflow before the
comparison and subtraction if the user configures a reset_interval_ms
greater than 4,294,967 (around 71.5 minutes).

While such a high interval is atypical for DAMON's continuous monitoring,
it is technically reachable via sysfs since the sysfs store function does
not bound the value beyond the maximum unsigned long value.

> +			else
> +				val = 0;
> +		}
> +		goal->current_value = val;
>  		return;
>  	}

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260929080113.41708-1-sj@kernel.org?part=1