linux-kernel - Re: [PATCH v2 1/2] hugetlbfs: use i_mmap_rwsem for more pmd sharing synchronization

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Date:   Mon, 30 Mar 2020 16:35:18 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Naresh Kamboju <naresh.kamboju@...aro.org>
Cc:     linux-mm <linux-mm@...ck.org>,
        open list <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...nel.org>,
        Hugh Dickins <hughd@...gle.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "Kirill A.Shutemov" <kirill.shutemov@...ux.intel.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Prakash Sangappa <prakash.sangappa@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        lkft-triage@...ts.linaro.org
Subject: Re: [PATCH v2 1/2] hugetlbfs: use i_mmap_rwsem for more pmd sharing
 synchronization

On 3/30/20 7:01 AM, Naresh Kamboju wrote:
> FYI,
> 
> The device is x86_64 device running i386 kernel image.
> 
> - Naresh
> 
> On Mon, 30 Mar 2020 at 19:00, Naresh Kamboju <naresh.kamboju@...aro.org> wrote:
>>
>> On i386 running LTP hugetlb tests found kernel BUG at fs/hugetlbfs/inode.c:458
>> Running Linux version 5.6.0-rc7-next-20200330
>> And hugemmap test failed due to ENOMEM.
>>
>> steps to reproduce:
>>         # cd /opt/ltp
>>         # ./runltp -f hugetlb

It took me a while to set up an environment to reproduce.  I was finally
able to reproduce on an x86_64 VM running a 32 bit OS/5.6.0-rc7-next-20200330
kernel.

My first attempt with PAE enabled and 8GB of memory did not reproduce.  When
I disabled PAE and dropped memory to 4GB, the problem reproduced.

After reverting this patch, and the followup in the series I was still able
to recreate the issue.  So, the patches are not the root cause.

One 'interesting' thing are the messages,
mm/pgtable-generic.c:50: bad pgd ...
These show up before the hugetlbfs BUG.

I will continue to investigate.  However, if the 'bad pgd ..' message provides
a hint to someone please let us know.
-- 
Mike Kravetz