Re: [RFC PATCH] mm/damon/core: filter out damos address filter-split failed region

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] mm/damon: unchecked damon_split_region_at() error in damos_filter_match()
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commit 881e287348e01011e3ec5442e7deb6f9c112db9c
Author: SJ Park <sj@kernel.org>

mm/damon/core: filter out damos address filter-split failed region

This commit updates damos_filter_match() and damos_core_filter_out() to
propagate errors from damon_split_region_at() and filter out the region if
splitting fails during DAMOS_FILTER_TYPE_ADDR evaluation.

> diff --git a/mm/damon/core.c b/mm/damon/core.c
> index b63e60ef89901..4d34587387456 100644
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c
> @@ -2551,13 +2551,14 @@ static void damos_update_stat(struct damos *s,
>  
>  static bool damos_filter_match(struct damon_ctx *ctx, struct damon_target *t,
>  		struct damon_region *r, struct damos_filter *filter,
> -		unsigned long min_region_sz)
> +		unsigned long min_region_sz, int *err)
>  {
>  	bool matched = false;
>  	struct damon_target *ti;
>  	int target_idx = 0;
>  	unsigned long start, end, wsum;
>  
> +	*err = 0;
>  	switch (filter->type) {
>  	case DAMOS_FILTER_TYPE_TARGET:
>  		damon_for_each_target(ti, ctx) {
> @@ -2588,7 +2589,9 @@ static bool damos_filter_match(struct damon_ctx *ctx, struct damon_target *t,
>  			break;
>  		}
>  		/* start inside the range */
> -		damon_split_region_at(t, r, end - r->ar.start);
> +		*err = damon_split_region_at(t, r, end - r->ar.start);
> +		if (*err)
> +			return false;
>  		matched = true;
>  		break;

[Severity: Medium]
Should the earlier damon_split_region_at() call in damos_filter_match()
when r->ar.start < start also propagate its return value via *err?

mm/damon/core.c:damos_filter_match() {
	case DAMOS_FILTER_TYPE_ADDR:
		...
		/* start before the range and overlap */
		if (r->ar.start < start) {
			damon_split_region_at(t, r, start - r->ar.start);
			matched = false;
			break;
		}
}

When a region starts before the filter range and overlaps it (r->ar.start <
start and r->ar.end > start), if damon_split_region_at(t, r, start -
r->ar.start) fails with -ENOMEM, r remains unsplit across [r->ar.start,
r->ar.end) while matched is set to false and *err remains 0.

If the filter is configured to exclude [start, end) (for example,
filter->matching == true and filter->allow == false with
s->core_filters_default_reject == false, or filter->matching == false and
filter->allow == true), kdamond_apply_schemes() -> damos_apply_scheme() ->
damos_core_filter_out() sees err == 0, does not reject r, and proceeds to
call c->ops.apply_scheme() on the entire unsplit region including the
excluded address range.

[ ... ]

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Sashiko AI review · https://sashiko.dev/#/patchset/20261018220253.158238-1-sj@kernel.org?part=1