Re: [RFC PATCH v2.2 22/28] mm/damon/core: introduce DAMON_FILTER_TYPE_MEMCG

[SeongJae Park <sj@kernel.org>]

On Fri, 15 May 2026 01:22:21 +0000 sashiko-bot@kernel.org wrote:

> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [High] Newly appended DAMON filters in `damon_commit_filters()` fail to copy the `memcg_id` field, leaving it uninitialized.
> --
> 
> commit 01e48275cc904a624a318c3fbc6c7313978207ef
> Author: SeongJae Park <sj@kernel.org>
> 
> mm/damon/core: introduce DAMON_FILTER_TYPE_MEMCG
> 
> This commit introduces a new DAMON filter type, DAMON_FILTER_TYPE_MEMCG,
> which allows monitoring and filtering based on specific memory cgroups.
> 
> > diff --git a/mm/damon/core.c b/mm/damon/core.c
> > index ab8ac9ec8450d..2d4a63dcc47fe 100644
> > --- a/mm/damon/core.c
> > +++ b/mm/damon/core.c
> > @@ -1422,6 +1422,13 @@ static void damon_commit_filter(struct damon_filter *dst,
> >  	dst->type = src->type;
> >  	dst->matching = src->matching;
> >  	dst->allow = src->allow;
> > +	switch (dst->type) {
> > +	case DAMON_FILTER_TYPE_MEMCG:
> > +		dst->memcg_id = src->memcg_id;
> > +		break;
> > +	default:
> > +		break;
> > +	}
> >  }
> >  
> >  static int damon_commit_filters(struct damon_probe *dst,
> 
> When new filters are appended during probe synchronization, does the
> memcg_id field remain uninitialized?
> 
> Looking at damon_commit_filters() which immediately follows this function,
> it creates new filters for any remaining source filters:
> 
> static int damon_commit_filters(...)
> {
> ...
> 	damon_for_each_filter_safe(src_filter, next, src) {
> 		if (j++ < i)
> 			continue;
> 
> 		new_filter = damon_new_filter(src_filter->type,
> 				src_filter->matching, src_filter->allow);
> 		if (!new_filter)
> 			return -ENOMEM;
> 		damon_add_filter(dst, new_filter);
> 	}
> ...
> }
> 
> Since damon_new_filter() only initializes the type, matching, and allow
> fields, and memcg_id is not manually copied here like it is in
> damon_commit_filter(), could this leave the newly appended filter's
> memcg_id with uninitialized memory?

Good finding.  I will set the new_filter->memcg_id as src_filter->memcg_id when
the type is DAMON_FILTER_TYPE_MEMCG.


Thanks,
SJ

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