linux-kernel - Re: [PATCH] hugetlb: fix pages per hugetlb calculation

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Message-ID: <20200629185434.GI25523@casper.infradead.org>
Date:   Mon, 29 Jun 2020 19:54:34 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Michal Hocko <mhocko@...nel.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>, stable@...nel.org
Subject: Re: [PATCH] hugetlb: fix pages per hugetlb calculation

On Mon, Jun 29, 2020 at 11:50:03AM -0700, Mike Kravetz wrote:
> The routine hpage_nr_pages() was incorrectly used to calculate the
> number of base pages in a hugetlb page.  hpage_nr_pages is designed
> to be called for THP pages and will return HPAGE_PMD_NR for hugetlb
> pages of any size.
> 
> Due to the context in which hpage_nr_pages was called, it is unlikely
> to produce a user visible error.  The routine with the incorrect call
> is only exercised in the case of hugetlb memory error or migration.
> In addition, this would need to be on an architecture which supports
> huge page sizes less than PMD_SIZE.  And, the vma containing the huge
> page would also need to smaller than PMD_SIZE.
> 
> Fixes: c0d0381ade79 ("hugetlbfs: use i_mmap_rwsem for more pmd sharing synchronization")
> Cc: stable@...nel.org
> Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>

Reviewed-by: Matthew Wilcox (Oracle) <willy@...radead.org>
Inadvertently-Reported-by: Matthew Wilcox (Oracle) <willy@...radead.org>