linux-kernel - Re: cgroup and FALLOC_FL_PUNCH_HOLE: WARNING: CPU: 13 PID: 2438 at mm/page_counter.c:57 page_counter

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Message-Id: <FF106FE1-E3DD-4A9B-B844-B04D0C26C403@redhat.com>
Date:   Wed, 21 Oct 2020 19:30:23 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     David Hildenbrand <david@...hat.com>,
        Michal Privoznik <mprivozn@...hat.com>,
        Mina Almasry <almasrymina@...gle.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Michal Hocko <mhocko@...nel.org>,
        Muchun Song <songmuchun@...edance.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Tejun Heo <tj@...nel.org>
Subject: Re: cgroup and FALLOC_FL_PUNCH_HOLE: WARNING: CPU: 13 PID: 2438 at mm/page_counter.c:57 page_counter_uncharge+0x4b/0x5


> Am 21.10.2020 um 18:58 schrieb Mike Kravetz <mike.kravetz@...cle.com>:
> 
>> 
>>> On 21.10.20 15:11, David Hildenbrand wrote:
>>> On 21.10.20 14:57, Michal Privoznik wrote:
>>>> On 10/21/20 5:35 AM, Mike Kravetz wrote:
>>>>> On 10/20/20 6:38 AM, David Hildenbrand wrote:
>>>>> It would be good if Mina (at least) would look these over.  Would also
>>>>> be interesting to know if these fixes address the bug seen with the qemu
>>>>> use case.
>>>>> I'm still doing more testing and code inspection to look for other issues.
> ...
> ...
>>>> I've applied, rebuilt and tested, but unfortunately I still hit the problem:
>>>> [ 6472.719047] ------------[ cut here ]------------
>>>> [ 6472.719052] WARNING: CPU: 6 PID: 11773 at mm/page_counter.c:57
> ...
> ...
>>> Agreed, same over here. :(
>> 
>> I *think* the following on top makes it fly
>> 
>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>> index 67fc6383995b..5cf7f6a6c1a6 100644
>> --- a/mm/hugetlb.c
>> +++ b/mm/hugetlb.c
>> @@ -656,6 +656,9 @@ static long region_del(struct resv_map *resv, long
>> f, long t)
>> 
>>                        del += t - f;
>> 
>> +                       hugetlb_cgroup_uncharge_file_region(
>> +                               resv, rg, t - f);
>> +
>>                        /* New entry for end of split region */
>>                        nrg->from = t;
>>                        nrg->to = rg->to;
>> @@ -667,9 +670,6 @@ static long region_del(struct resv_map *resv, long
>> f, long t)
>>                        /* Original entry is trimmed */
>>                        rg->to = f;
>> 
>> -                       hugetlb_cgroup_uncharge_file_region(
>> -                               resv, rg, nrg->to - nrg->from);
>> -
>>                        list_add(&nrg->link, &rg->link);
>>                        nrg = NULL;
>>                        break;
> 
> Thanks, yes that certainly does look like a bug in that code.
> 
> Does that resolve the issue with quemu?

I was not able to reproduce, so I guess we found all issues!

Thanks!

> 
> I want to do a little more testing/research before sending a patch later
> today.
> -- 
> Mike Kravetz