linux-kernel - Re: [PATCH] hugetlb: fix uninitialized subpool pointer

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Message-ID: <ef62ac45-9ec9-2582-3e58-7efc0609221f@oracle.com>
Date:   Tue, 23 Feb 2021 15:21:58 -0800
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Oscar Salvador <osalvador@...e.de>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
        Michal Hocko <mhocko@...e.com>,
        Muchun Song <songmuchun@...edance.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] hugetlb: fix uninitialized subpool pointer

On 2/23/21 2:58 PM, Oscar Salvador wrote:
> On 2021-02-23 23:55, Mike Kravetz wrote:
>> Yes, that is the more common case where the once active hugetlb page
>> will be simply added to the free list via enqueue_huge_page().  This
>> path does not go through prep_new_huge_page.
> 
> Right, I see.
> 
> Thanks

You got me thinking ...
When we dynamically allocate gigantic pages via alloc_contig_pages, we
will not use the buddy allocator.  Therefore, the usual 'page prepping'
will not take place.  Specifically, I could not find anything in that
path which clears page->private of the head page.
Am I missing that somewhere?  If not, then we need to clear that as well
in prep_compound_gigantic_page.  Or, just clear it in prep_new_huge_page
to handle any change in assumptions about the buddy allocator.

This is not something introduced with the recent field shuffling, it
looks like something that existed for some time.
-- 
Mike Kravetz