Re: [RFC PATCH 2/3] mm/damon/core: avoid overflows in monitoring results calculations

[sashiko-bot@kernel.org]

> When monitoring intervals change, DAMON converts region ages and sample
> counts for the new intervals.  The conversions overflow before division:
> 
> - damon_age_for_new_attrs() multiplies the age by the old aggregation
>   interval in unsigned long.  On 32-bit kernels, the default 100 ms
>   interval makes this overflow after about 72 minutes.
> - The sample ratio conversions multiply unsigned int values.  They can
>   overflow on every architecture when an aggregation has more than
>   429,496 samples, such as a 1 ms sample interval and a 430 second
>   aggregation interval.
> 
> The moving sums also use mult_frac() for the fraction of an aggregation
> window that remains and for the previous window's contribution.  On
> 32-bit kernels, both can overflow with long aggregation intervals.  For
> example, 500,000 remaining samples of a 600,000-sample window are
> [ ... ]
> 
> Fixes: 2f5bef5a590b ("mm/damon/core: update monitoring results for new monitoring attributes")
> Fixes: 9f3786d8602f ("mm/damon/core: introduce damon_nr_accesses_mvsum()")
> Fixes: 2ec26dd341d1 ("mm/damon/core: introduce damon_probe_hits_mvsum()")
> Signed-off-by: DaeMyung Kang <charsyam@gmail.com>

Sashiko has reviewed this patch and found no issues.

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