From mboxrd@z Thu Jan  1 00:00:00 1970
From: =?UTF-8?Q?Mika_Penttil=c3=a4?= <mika.penttila@nextfour.com>
Subject: Re: [PATCH v5 01/12] mm: support madvise(MADV_FREE)
Date: Mon, 30 Nov 2015 10:20:25 +0200
Message-ID: <565C06C9.7040906@nextfour.com>
References: <1448865583-2446-1-git-send-email-minchan@kernel.org>
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To: Minchan Kim <minchan@kernel.org>, Andrew Morton <akpm@linux-foundation.org>
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> +		 * If pmd isn't transhuge but the page is THP and
> +		 * is owned by only this process, split it and
> +		 * deactivate all pages.
> +		 */
> +		if (PageTransCompound(page)) {
> +			if (page_mapcount(page) != 1)
> +				goto out;
> +			get_page(page);
> +			if (!trylock_page(page)) {
> +				put_page(page);
> +				goto out;
> +			}
> +			pte_unmap_unlock(orig_pte, ptl);
> +			if (split_huge_page(page)) {
> +				unlock_page(page);
> +				put_page(page);
> +				pte_offset_map_lock(mm, pmd, addr, &ptl);
> +				goto out;
> +			}
> +			pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
> +			pte--;
> +			addr -= PAGE_SIZE;
> +			continue;
> +		}

looks like this leaks page count if split_huge_page() is succesfull
(returns zero).

--Mika