From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx153.postini.com [74.125.245.153]) by kanga.kvack.org (Postfix) with SMTP id D34246B006E for ; Tue, 27 Nov 2012 16:54:59 -0500 (EST) Date: Tue, 27 Nov 2012 13:54:58 -0800 From: Andrew Morton Subject: Re: [PATCH] mm, soft offline: split thp at the beginning of soft_offline_page() Message-Id: <20121127135458.4b7369f7.akpm@linux-foundation.org> In-Reply-To: <1354050331-26844-1-git-send-email-n-horiguchi@ah.jp.nec.com> References: <1354050331-26844-1-git-send-email-n-horiguchi@ah.jp.nec.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Naoya Horiguchi Cc: Tony Luck , Andi Kleen , Wu Fengguang , linux-kernel@vger.kernel.org, linux-mm@kvack.org 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? -- 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