Re: [syzbot] [damon?] divide error in damon_set_attrs

[Kefeng Wang]

On 2023/5/27 9:46, SeongJae Park wrote:
> Hi Kefeng,
>
> On Sat, 27 May 2023 09:15:01 +0800 Kefeng Wang <wangkefeng.wang@xxxxxxxxxx> wrote:
>
> [...]
> > > Nice and effective fix!  Nevertheless, I think aggregation interval smaller
> > > than sample interval is just a wrong input.  How about adding the check in
> > > damon_set_attrs()'s already existing attributes validation, like below?
> >
> > Yes, move the check into damon_set_attrs() is better
>
> Thank you for this kind comment!
>
> > , and it seems that
> > we could move all the check into it, and drop the old_attrs check in
> > damon_update_monitoring_results(), what's you option?
> >
> >
> > diff --git a/mm/damon/core.c b/mm/damon/core.c
> > index d9ef62047bf5..1647f7f1f708 100644
> > --- a/mm/damon/core.c
> > +++ b/mm/damon/core.c
> > @@ -523,12 +523,6 @@ static void damon_update_monitoring_results(struct
> > damon_ctx *ctx,
> >           struct damon_target *t;
> >           struct damon_region *r;
> >
> > -       /* if any interval is zero, simply forgive conversion */
> > -       if (!old_attrs->sample_interval || !old_attrs->aggr_interval ||
> > -                       !new_attrs->sample_interval ||
> > -                       !new_attrs->aggr_interval)
> > -               return;
> > -
> >           damon_for_each_target(t, ctx)
> >                   damon_for_each_region(r, t)
> >                           damon_update_monitoring_result(
> > @@ -551,6 +545,10 @@ int damon_set_attrs(struct damon_ctx *ctx, struct
> > damon_attrs *attrs)
> >                   return -EINVAL;
> >           if (attrs->min_nr_regions > attrs->max_nr_regions)
> >                   return -EINVAL;
> > +       if (attrs->sample_interval > attrs->aggr_interval)
> > +               return -EINVAL;
> > +       if (!attrs->sample_interval || !attrs->aggr_interval)
> > +               return -EINVAL;
>
> In my humble opinion, the validation for monitoring results and for general
> monitoring could be different.  For example, zero aggreation/sampling intervals
> might make sense for fixed granularity working set size monitoring.  Hence, I'd
> prefer keeping those checks in the damon_update_monitoring_results().


ok, will keep that, I check the damon_set_attrs() called by 
lru_sort/reclaim monitor and sysfs/dbgfs, the above changes should be 
ok, maybe missing something, the working set size monitoring is not 
public for now?

> Thanks,
> SJ
>
> [...]