Re: [PATCH 15/19] mm/damon/core: implement damon_has_probe_weight()

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Setting probe weights unconditionally disables access checks without validating if the active operation set supports data attribute probes (`apply_probes`), silently breaking monitoring.
--

--- Patch [15]: [PATCH 15/19] mm/damon/core: implement damon_has_probe_weight() ---
commit 7b3dfd9b2d27b35cdf18598b48bc4927675cb47a
Author: SJ Park <sj@kernel.org>

mm/damon/core: implement damon_has_probe_weight()

This commit updates damon_has_probe_weights() to properly iterate over the
probes and return true if any probe has a weight configured. This enables the
data attribute monitoring mode that previously returned false intentionally
during incremental development.

> diff --git a/mm/damon/core.c b/mm/damon/core.c
> index 91964336ce31e..806a67d02a6e9 100644
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c
> @@ -211,6 +211,12 @@ static struct damon_probe *damon_nth_probe(int n, struct damon_ctx *ctx)
>  
>  static bool damon_has_probe_weights(struct damon_ctx *c)
>  {
> +	struct damon_probe *p;
> +
> +	damon_for_each_probe(p, c) {
> +		if (p->weight)
> +			return true;
> +	}

[Severity: High]
If a user configures a DAMON context with an operation set that does not
implement apply_probes (e.g. vaddr operations) and adds a probe with a
non-zero weight, will this silently break monitoring?

With this change, damon_has_probe_weights() returning true will skip
standard access monitoring in kdamond_fn():

mm/damon/core.c:kdamond_fn() {
...
	bool access_check_disabled = damon_has_probe_weights(ctx);
	unsigned int max_merge_score = 0;
...
	if (!access_check_disabled && ctx->ops.check_accesses)
		max_merge_score = ctx->ops.check_accesses(ctx);

	if (ctx->ops.apply_probes) {
		/* bypassed if apply_probes is not implemented */
		...
	}
...
	/* max_merge_score remains 0 */
	if (time_after_eq(ctx->passed_sample_intervals,
				next_aggregation_sis)) {
		kdamond_merge_regions(ctx, max_merge_score / 10, sz_limit);
...
}

Should damon_valid_probe_params() or damon_has_probe_weights() also verify
that ctx->ops.apply_probes is implemented before allowing this mode, to
prevent kdamond_merge_regions() from unconditionally merging regions with
a threshold of 0?

>  	return false;
>  }

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260710134651.18084-1-sj@kernel.org?part=15