Re: [PATCH 6.1.y v3 1/2] mm/damon/core: do non-safe region walk on kdamond_apply_schemes()

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] mm/damon: double-application of earlier schemes to newly split regions
--

commit 01d768c4d318527360ef5913771d20f22a99984a
Author: SeongJae Park <sj@kernel.org>

mm/damon/core: do non-safe region walk on kdamond_apply_schemes()

kdamond_apply_schemes() is using damon_for_each_region_safe(), which is
safe for deallocation of the region inside the loop. However, the loop
internal logic does not deallocate regions. Hence it is only wasting the
next pointer.

Link: https://lkml.kernel.org/r/20260227170623.95384-3-sj@kernel.org

> diff --git a/mm/damon/core.c b/mm/damon/core.c
> index 7afbc20833ea4..b5c85e6488596 100644
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c

[ ... ]

> @@ -912,7 +911,7 @@ static void kdamond_apply_schemes(struct damon_ctx *c)
>  	}
>  
>  	damon_for_each_target(t, c) {
> -		damon_for_each_region_safe(r, next_r, t)
> +		damon_for_each_region(r, t)
>  			damon_do_apply_schemes(c, t, r);

[Severity: High]
Does this code cause earlier schemes to be applied twice to newly split
regions?

If multiple schemes are configured, an earlier scheme (e.g. Scheme 0) might
apply its action to a full, un-split region. If a later scheme (e.g.
Scheme 1) then decides to split the region, damon_split_region_at() inserts
the newly split part into the list immediately after the current region.

Because this loop in kdamond_apply_schemes() now uses
damon_for_each_region() instead of the safe variant, the outer loop will
advance to this newly split region and call damon_do_apply_schemes() on it
again.

Will this cause damon_do_apply_schemes() to evaluate the new region from
the beginning of the scheme list, resulting in Scheme 0 executing its
memory management actions (like madvise) and counting statistics a second
time on the same memory range?

>  	}
>  }

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261010063042.8611-1-sj@kernel.org?part=1