Re: [RFC PATCH 3/8] mm/damon/ops-common: support hugepage_size damon filter matching

[SJ Park <sj@kernel.org>]

On Sun, 13 Sep 2026 17:24:42 +0000 sashiko-bot@kernel.org wrote:

> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [High] damon_commit_filters() leaves range_min and range_max uninitialized for appended hugepage_size filters.
> --
> 
> commit 377608c283881250a794879309e80b931825b0d3
> Author: SJ Park <sj@kernel.org>
> 
> mm/damon/ops-common: support hugepage_size damon filter matching
> 
> Update ops-common data attribute filter matching logic to support
> hugepage_size filter type.
> 
> > diff --git a/mm/damon/ops-common.c b/mm/damon/ops-common.c
> > index c36cc39cd2c70..77366f42b3e5b 100644
> > --- a/mm/damon/ops-common.c
> > +++ b/mm/damon/ops-common.c
> 
> [ ... ]
> 
> > @@ -558,6 +559,15 @@ bool damon_ops_filter_match(struct damon_filter *filter, struct folio *folio)
> >  			matched = filter->memcg_id == mem_cgroup_id(memcg);
> >  		rcu_read_unlock();
> >  		break;
> > +	case DAMON_FILTER_TYPE_HUGEPAGE_SIZE:
> > +		if (!folio) {
> > +			matched = false;
> > +			break;
> > +		}
> > +		folio_sz = folio_size(folio);
> > +		matched = filter->range_min <= folio_sz &&
> > +			folio_sz <= filter->range_max;
> > +		break;
> 
> [Severity: High]
> Does this new filter type need to be explicitly copied when a newly appended
> filter is committed?
> 
> When userspace adds a new filter to an existing DAMON probe via sysfs,
> damon_commit_filters() in mm/damon/core.c invokes damon_new_filter() which
> allocates memory without zeroing it. The attributes are then copied in a
> switch block:
> 
> mm/damon/core.c:damon_commit_filters() {
> 	...
> 	new_filter = damon_new_filter(src_filter->type,
> 			src_filter->matching, src_filter->allow);
> 	if (!new_filter)
> 		return -ENOMEM;
> 	switch (src_filter->type) {
> 	case DAMON_FILTER_TYPE_MEMCG:
> 		new_filter->memcg_id = src_filter->memcg_id;
> 		break;
> 	default:
> 		break;
> 	}
> 	damon_add_filter(dst, new_filter);
> 	...
> }
> 
> Because DAMON_FILTER_TYPE_HUGEPAGE_SIZE is missing from this switch block,
> range_min and range_max will be left uninitialized for appended filters. This
> could result in the filtering logic using garbage memory values.
> 
> Should DAMON_FILTER_TYPE_HUGEPAGE_SIZE be added to this switch statement
> so the range boundaries are properly copied to the new filter?

No issue.  DAMON sysfs is not allowing hugepage_size probe filter at this
moment.  Later, it will add the support with proper range setup.

> 
> >  	default:
> >  		break;
> >  	}
> 
> -- 
> Sashiko AI review · https://sashiko.dev/#/patchset/20260913171133.102366-1-sj@kernel.org?part=3


Thanks,
SJ