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Date: Tue, 13 Oct 2015 18:10:53 +0900
From: Minchan Kim <minchan@kernel.org>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        "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
Message-ID: <20151013091053.GA6630@bbox>
References: <1444703918-16597-1-git-send-email-minchan@kernel.org>
 <561CB297.9080600@suse.cz>
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On Tue, Oct 13, 2015 at 09:28:23AM +0200, Vlastimil Babka wrote:
> 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>

Thanks for the detail and review, Vlastimil.