linux-kernel - Re: [PATCH] mm: hugetlb_vmemmap: fix a race between vmemmap pmd split

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Date:   Mon, 14 Aug 2023 15:28:39 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     muchun.song@...ux.dev, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: hugetlb_vmemmap: fix a race between vmemmap pmd split

On 07/07/23 11:38, Muchun Song wrote:
> The local variable @page in __split_vmemmap_huge_pmd() to obtain a pmd
> page without holding page_table_lock may possiblely get the page table
> page instead of a huge pmd page.  The effect may be in set_pte_at()
> since we may pass an invalid page struct, if set_pte_at() wants to
> access the page struct (e.g. CONFIG_PAGE_TABLE_CHECK is enabled), it
> may crash the kernel.  So fix it. And inline __split_vmemmap_huge_pmd()
> since it only has one user.
> 
> Fixes: d8d55f5616cf ("mm: sparsemem: use page table lock to protect kernel pmd operations")
> Signed-off-by: Muchun Song <songmuchun@...edance.com>
> ---
>  mm/hugetlb_vmemmap.c | 34 ++++++++++++++--------------------
>  1 file changed, 14 insertions(+), 20 deletions(-)

Sorry, for the very late reply!

This code looks fine to me,
Reviewed-by: Mike Kravetz <mike.kravetz@...cle.com>

The discussion about 'open code' or inline' has me a bit confused.  I am
perfectly happy with the code as it is.

When I hear/see inline, I think of the inline function keyword.  Since that
is not happening in this patch, the mention of 'inline
__split_vmemmap_huge_pmd()' does cause me to think a bit more than usual.

Yes, the backports will need to be modified.
-- 
Mike Kravetz