Re: [PATCH 4/7] mm/damon/core: s/nr_accesses_to_accesses_bp/sample_count_to_bp/

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [High] The functions `damon_sample_bp_to_count` and `damon_sample_count_to_bp` are susceptible to 32-bit integer overflows when evaluating large aggregation intervals.
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--- Patch [4]: [PATCH 4/7] mm/damon/core: s/nr_accesses_to_accesses_bp/sample_count_to_bp/ ---
commit 75d19025f9846da2b8b1718a4f36d8064a4aa832
Author: SJ Park <sj@kernel.org>

mm/damon/core: s/nr_accesses_to_accesses_bp/sample_count_to_bp/

This commit renames damon_nr_accesses_to_accesses_bp to
damon_sample_count_to_bp to better describe its actual behavior of
converting a positive sample count to a ratio.

> diff --git a/mm/damon/core.c b/mm/damon/core.c
> index dea63083917b0..718268df27fa7 100644
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c
> @@ -883,19 +883,18 @@ static unsigned int damon_sample_bp_to_count(
>  	return bp * damon_nr_samples_per_aggr(attrs) / 10000;
>  }

[Severity: High]
This is a pre-existing issue, but does this multiplication overflow if the
total samples in an aggregation interval is large?

If an administrator configures a large aggr_interval compared to
sample_interval, making the sample ratio exceed 429,496, multiplying bp
(up to 10,000) by the number of samples could exceed the 32-bit limit of
unsigned int, causing incorrect bound calculations.

>  
> -/* Convert nr_accesses to access ratio in bp (per 10,000) */
> -static unsigned int damon_nr_accesses_to_accesses_bp(
> -		unsigned int nr_accesses, struct damon_attrs *attrs)
> +/* convert sample count to ratio in bp (per 10,000) */
> +static unsigned int damon_sample_count_to_bp(
> +		unsigned int count, struct damon_attrs *attrs)
>  {
> -	return mult_frac(nr_accesses, 10000, damon_nr_samples_per_aggr(attrs));
> +	return mult_frac(count, 10000, damon_nr_samples_per_aggr(attrs));
>  }

[Severity: High]
This is also a pre-existing issue, but can this use of mult_frac result in
an integer overflow?

The mult_frac macro evaluates (count % samples) * 10000 in 32-bit
arithmetic, which might overflow and produce an incorrect basis point
ratio when the sample count is very large.

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Sashiko AI review · https://sashiko.dev/#/patchset/20260708135359.122587-1-sj@kernel.org?part=4