linux-kernel - Re: [syzbot] [damon?] divide error in damon_set

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Date:   Sat, 27 May 2023 10:02:38 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     SeongJae Park <sj@...nel.org>
CC:     syzbot <syzbot+841a46899768ec7bec67@...kaller.appspotmail.com>,
        <akpm@...ux-foundation.org>, <damon@...ts.linux.dev>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        <syzkaller-bugs@...glegroups.com>
Subject: Re: [syzbot] [damon?] divide error in damon_set_attrs



On 2023/5/27 9:46, SeongJae Park wrote:
> Hi Kefeng,
> 
> On Sat, 27 May 2023 09:15:01 +0800 Kefeng Wang <wangkefeng.wang@...wei.com> 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
> 
> [...]