From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx117.postini.com [74.125.245.117]) by kanga.kvack.org (Postfix) with SMTP id 1543F6B004D for ; Tue, 27 Nov 2012 17:42:55 -0500 (EST) From: Naoya Horiguchi Subject: Re: [PATCH] mm, soft offline: split thp at the beginning of soft_offline_page() Date: Tue, 27 Nov 2012 17:42:43 -0500 Message-Id: <1354056163-30558-1-git-send-email-n-horiguchi@ah.jp.nec.com> In-Reply-To: <20121127135458.4b7369f7.akpm@linux-foundation.org> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Naoya Horiguchi , Tony Luck , Andi Kleen , Wu Fengguang , linux-kernel@vger.kernel.org, linux-mm@kvack.org On Tue, Nov 27, 2012 at 01:54:58PM -0800, Andrew Morton wrote: > On Tue, 27 Nov 2012 16:05:31 -0500 > Naoya Horiguchi wrote: > > > When we try to soft-offline a thp tail page, put_page() is called on the > > tail page unthinkingly and VM_BUG_ON is triggered in put_compound_page(). > > This patch splits thp before going into the main body of soft-offlining. > > > > The interface of soft-offlining is open for userspace, so this bug can > > lead to DoS attack and should be fixed immedately. > > > > Signed-off-by: Naoya Horiguchi > > Cc: stable@vger.kernel.org > > --- > > mm/memory-failure.c | 8 ++++++++ > > 1 file changed, 8 insertions(+) > > > > diff --git v3.7-rc7.orig/mm/memory-failure.c v3.7-rc7/mm/memory-failure.c > > index 8fe3640..e48e235 100644 > > --- v3.7-rc7.orig/mm/memory-failure.c > > +++ v3.7-rc7/mm/memory-failure.c > > @@ -1548,9 +1548,17 @@ int soft_offline_page(struct page *page, int flags) > > { > > int ret; > > unsigned long pfn = page_to_pfn(page); > > + struct page *hpage = compound_trans_head(page); > > > > if (PageHuge(page)) > > return soft_offline_huge_page(page, flags); > > + if (PageTransHuge(hpage)) { > > + if (PageAnon(hpage) && unlikely(split_huge_page(hpage))) { > > + pr_info("soft offline: %#lx: failed to split THP\n", > > + pfn); > > + return -EBUSY; > > + } > > + } > > We can use PageTransCompound() here, as we know it isn't a hugetlbfs > page. This will then permit the PageAnon() test to be omitted, methinks? Using PageTransCompound() is OK for me. But without this PageAnon() test, we can trigger BUG_ON(!PageAnon) inside split_huge_page() when soft offlining is kicked on non-huge compound pages. The point about telling thp from hugetlbfs pages and non-huge compound pages was discussed last month over 7a71932d5676b7410 ("kpageflags: fix wrong KPF_THP on non-huge compound pages"), where we used a bit tricky workaround of using PageTransCompound(page) && PageLRU(compound_trans_head(page)). Thanks, Naoya -- 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