linux-kernel - Re: [PATCH v1] hugetlb: pass head page to remove_hugetlb

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Date:   Thu, 27 May 2021 14:12:21 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     Naoya Horiguchi <nao.horiguchi@...il.com>, linux-mm@...ck.org,
        Oscar Salvador <osalvador@...e.de>,
        Muchun Song <songmuchun@...edance.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] hugetlb: pass head page to remove_hugetlb_page()

On 5/27/21 12:54 PM, Michal Hocko wrote:
> On Thu 27-05-21 09:28:51, Mike Kravetz wrote:
>> On 5/26/21 4:52 PM, Naoya Horiguchi wrote:
>>> From: Naoya Horiguchi <naoya.horiguchi@....com>
>>>
>>> remove_hugetlb_page() dereferences page->lru, so it's assumed that the
>>> page points to a head page, but one of the caller,
>>> dissolve_free_huge_page(), provides remove_hugetlb_page() with 'page'
>>> which could be a tail page.  So pass 'head' to it, instead.
>>>
>>
>> I believe we have the same problem later in the routine when calling
>> add_hugetlb_page()?
> 
> Can we ever get a tail page there?
> 

Yes.  Actually alloc_huge_page_vmemmap() and add_hugetlb_page() calls
later in the same block of code expect head page but we pass 'page' which
could be a tail page.

>> If so, should we combine the changes?  Or, do we need two patches as
>> the bugs were introduced with different commits?
> 
> If there is an issue then I would go with a separate patch.
> 

The calls to alloc_huge_page_vmemmap() and add_hugetlb_page() are only
in Andrew's tree (and next).  So, they can be fixed there.

I'll send a patch shortly.
-- 
Mike Kravetz