From: Vlastimil Babka <vbabka@suse.cz>
To: Minchan Kim <minchan@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>,
Mel Gorman <mgorman@suse.de>,
Andrea Arcangeli <aarcange@redhat.com>,
Hugh Dickins <hughd@google.com>, Rik van Riel <riel@redhat.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
stable@vger.kernel.org,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [PATCH v2] thp: use is_zero_pfn only after pte_present check
Date: Tue, 13 Oct 2015 09:28:23 +0200 [thread overview]
Message-ID: <561CB297.9080600@suse.cz> (raw)
In-Reply-To: <1444703918-16597-1-git-send-email-minchan@kernel.org>
On 10/13/2015 04:38 AM, Minchan Kim wrote:
> Use is_zero_pfn on pteval only after pte_present check on pteval
> (It might be better idea to introduce is_zero_pte where checks
> pte_present first). Otherwise, it could work with swap or
> migration entry and if pte_pfn's result is equal to zero_pfn
> by chance, we lose user's data in __collapse_huge_page_copy.
> So if you're luck, the application is segfaulted and finally you
> could see below message when the application is exit.
>
> BUG: Bad rss-counter state mm:ffff88007f099300 idx:2 val:3
>
> Cc: <stable@vger.kernel.org>
More specific:
Cc: <stable@vger.kernel.org> # 4.1+
Fixes: ca0984caa823 ("mm: incorporate zero pages into transparent huge
pages")
> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
> Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
> Signed-off-by: Minchan Kim <minchan@kernel.org>
> ---
> Hello Greg,
>
> This patch should go to -stable but when you will apply it
> after merging of linus tree, it will be surely conflicted due
> to userfaultfd part.
>
> I want to know how to handle it.
>
> Thanks.
>
> mm/huge_memory.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 4b06b8db9df2..bbac913f96bc 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2206,7 +2206,8 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
> for (_pte = pte; _pte < pte+HPAGE_PMD_NR;
> _pte++, address += PAGE_SIZE) {
> pte_t pteval = *_pte;
> - if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
> + if (pte_none(pteval) || (pte_present(pteval) &&
> + is_zero_pfn(pte_pfn(pteval)))) {
> if (!userfaultfd_armed(vma) &&
> ++none_or_zero <= khugepaged_max_ptes_none)
> continue;
>
--
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next prev parent reply other threads:[~2015-10-13 7:28 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-13 2:38 [PATCH v2] thp: use is_zero_pfn only after pte_present check Minchan Kim
2015-10-13 5:41 ` Greg Kroah-Hartman
2015-10-13 6:26 ` Minchan Kim
2015-10-13 7:28 ` Vlastimil Babka [this message]
2015-10-13 9:10 ` Minchan Kim
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