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

[SJ Park <sj@kernel.org>]

On Wed, 08 Jul 2026 14:03:47 +0000 sashiko-bot@kernel.org wrote:

> 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.
> --
> 
> --- 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.

Known low priority issue.

> 
> >  
> > -/* 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.

Known low priorrity issue.

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


Thanks,
SJ