From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f169.google.com (mail-wi0-f169.google.com [209.85.212.169]) by kanga.kvack.org (Postfix) with ESMTP id 06E156B0254 for ; Mon, 12 Oct 2015 06:13:23 -0400 (EDT) Received: by wicgb1 with SMTP id gb1so44166522wic.1 for ; Mon, 12 Oct 2015 03:13:22 -0700 (PDT) Received: from mail-wi0-f175.google.com (mail-wi0-f175.google.com. [209.85.212.175]) by mx.google.com with ESMTPS id y2si14935687wib.45.2015.10.12.03.13.21 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 12 Oct 2015 03:13:22 -0700 (PDT) Received: by wicgb1 with SMTP id gb1so142702514wic.1 for ; Mon, 12 Oct 2015 03:13:21 -0700 (PDT) Date: Mon, 12 Oct 2015 13:13:20 +0300 From: "Kirill A. Shutemov" Subject: Re: [PATCH] thp: use is_zero_pfn after pte_present check Message-ID: <20151012101320.GB2544@node> References: <1444614856-18543-1-git-send-email-minchan@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1444614856-18543-1-git-send-email-minchan@kernel.org> Sender: owner-linux-mm@kvack.org List-ID: To: Minchan Kim Cc: Andrew Morton , Mel Gorman , Vlastimil Babka , Andrea Arcangeli , Hugh Dickins , Rik van Riel , linux-kernel@vger.kernel.org, linux-mm@kvack.org On Mon, Oct 12, 2015 at 10:54:16AM +0900, 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 Did you acctually steped on the bug? If yes it's subject for stable@, I think. > Signed-off-by: Minchan Kim > --- > > I found this bug with MADV_FREE hard test. Sometime, I saw > "Bad rss-counter" message with MM_SWAPENTS but it's really > rare, once a day if I was luck or once in five days if I was > unlucky so I am doing test still and just pass a few days but > I hope it will fix the issue. > > mm/huge_memory.c | 12 +++++++++++- > 1 file changed, 11 insertions(+), 1 deletion(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 4b06b8db9df2..349590aa4533 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -2665,15 +2665,25 @@ static int khugepaged_scan_pmd(struct mm_struct *mm, > for (_address = address, _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)) { In -mm tree we have is_swap_pte() check before this point in khugepaged_scan_pmd() Also, what about similar pattern in __collapse_huge_page_isolate() and __collapse_huge_page_copy()? Shouldn't they be fixed as well? > if (!userfaultfd_armed(vma) && > ++none_or_zero <= khugepaged_max_ptes_none) > continue; > else > goto out_unmap; > } > + > if (!pte_present(pteval)) > goto out_unmap; > + > + if (is_zero_pfn(pte_pfn(pteval))) { > + if (!userfaultfd_armed(vma) && > + ++none_or_zero <= khugepaged_max_ptes_none) > + continue; > + else > + goto out_unmap; > + } > + > if (pte_write(pteval)) > writable = true; > > -- > 1.9.1 > -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org