Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S936644Ab3DJUVe (ORCPT ); Wed, 10 Apr 2013 16:21:34 -0400 Received: from mail-ee0-f48.google.com ([74.125.83.48]:64440 "EHLO mail-ee0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S936370Ab3DJUVb (ORCPT ); Wed, 10 Apr 2013 16:21:31 -0400 Date: Wed, 10 Apr 2013 22:21:27 +0200 From: Michal Hocko To: Naoya Horiguchi Cc: Andrew Morton , Mel Gorman , Hugh Dickins , Rik van Riel , KOSAKI Motohiro , Konstantin Khlebnikov , HATAYAMA Daisuke , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [RESEND][PATCH v5 3/3] hugetlbfs: add swap entry check in follow_hugetlb_page() Message-ID: <20130410202127.GA30063@dhcp22.suse.cz> References: <1365610669-16625-1-git-send-email-n-horiguchi@ah.jp.nec.com> <1365610669-16625-4-git-send-email-n-horiguchi@ah.jp.nec.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1365610669-16625-4-git-send-email-n-horiguchi@ah.jp.nec.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3613 Lines: 92 On Wed 10-04-13 12:17:49, Naoya Horiguchi wrote: > # I suspended Reviewed and Acked given for the previous version, because > # it has a non-minor change. If you want to restore it, please let me know. > ----- > With applying the previous patch "hugetlbfs: stop setting VM_DONTDUMP in > initializing vma(VM_HUGETLB)" to reenable hugepage coredump, if a memory > error happens on a hugepage and the affected processes try to access > the error hugepage, we hit VM_BUG_ON(atomic_read(&page->_count) <= 0) > in get_page(). > > The reason for this bug is that coredump-related code doesn't recognise > "hugepage hwpoison entry" with which a pmd entry is replaced when a memory > error occurs on a hugepage. > In other words, physical address information is stored in different bit layout > between hugepage hwpoison entry and pmd entry, so follow_hugetlb_page() > which is called in get_dump_page() returns a wrong page from a given address. > > The expected behavior is like this: > > absent is_swap_pte FOLL_DUMP Expected behavior > ------------------------------------------------------------------- > true false false hugetlb_fault > false true false hugetlb_fault > false false false return page > true false true skip page (to avoid allocation) > false true true hugetlb_fault > false false true return page > > With this patch, we can call hugetlb_fault() and take proper actions > (we wait for migration entries, fail with VM_FAULT_HWPOISON_LARGE for > hwpoisoned entries,) and as the result we can dump all hugepages except > for hwpoisoned ones. > > ChangeLog v5: > - improve comment and description. > > ChangeLog v4: > - move is_swap_page() to right place. > > ChangeLog v3: > - add comment about using is_swap_pte() > > Signed-off-by: Naoya Horiguchi > Cc: stable@vger.kernel.org Acked-by: Michal Hocko Thanks! > --- > mm/hugetlb.c | 12 +++++++++++- > 1 file changed, 11 insertions(+), 1 deletion(-) > > diff --git v3.9-rc3.orig/mm/hugetlb.c v3.9-rc3/mm/hugetlb.c > index 0d1705b..bf26ee8 100644 > --- v3.9-rc3.orig/mm/hugetlb.c > +++ v3.9-rc3/mm/hugetlb.c > @@ -2983,7 +2983,17 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma, > break; > } > > - if (absent || > + /* > + * We need call hugetlb_fault for both hugepages under migration > + * (in which case hugetlb_fault waits for the migration,) and > + * hwpoisoned hugepages (in which case we need to prevent the > + * caller from accessing to them.) In order to do this, we use > + * here is_swap_pte instead of is_hugetlb_entry_migration and > + * is_hugetlb_entry_hwpoisoned. This is because it simply covers > + * both cases, and because we can't follow correct pages > + * directly from any kind of swap entries. > + */ > + if (absent || is_swap_pte(huge_ptep_get(pte)) || > ((flags & FOLL_WRITE) && !pte_write(huge_ptep_get(pte)))) { > int ret; > > -- > 1.7.11.7 > > -- > 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 -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/