Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754200Ab2FKHWa (ORCPT ); Mon, 11 Jun 2012 03:22:30 -0400 Received: from fgwmail5.fujitsu.co.jp ([192.51.44.35]:36910 "EHLO fgwmail5.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751666Ab2FKHW2 (ORCPT ); Mon, 11 Jun 2012 03:22:28 -0400 X-SecurityPolicyCheck: OK by SHieldMailChecker v1.7.4 Message-ID: <4FD59C31.6000606@jp.fujitsu.com> Date: Mon, 11 Jun 2012 16:20:17 +0900 From: Kamezawa Hiroyuki User-Agent: Mozilla/5.0 (Windows NT 6.0; rv:12.0) Gecko/20120428 Thunderbird/12.0.1 MIME-Version: 1.0 To: Minchan Kim CC: Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrea Arcangeli , Mel Gorman , Michal Hocko Subject: Re: [PATCH] mm: do not use page_count without a page pin References: <1339373872-31969-1-git-send-email-minchan@kernel.org> In-Reply-To: <1339373872-31969-1-git-send-email-minchan@kernel.org> Content-Type: text/plain; charset=ISO-2022-JP Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1838 Lines: 53 (2012/06/11 9:17), Minchan Kim wrote: > d179e84ba fixed the problem[1] in vmscan.c but same problem is here. > Let's fix it. > > [1] http://comments.gmane.org/gmane.linux.kernel.mm/65844 > > I copy and paste d179e84ba's contents for description. > > "It is unsafe to run page_count during the physical pfn scan because > compound_head could trip on a dangling pointer when reading > page->first_page if the compound page is being freed by another CPU." > > Cc: Andrea Arcangeli > Cc: Mel Gorman > Cc: Michal Hocko > Cc: KAMEZAWA Hiroyuki > Signed-off-by: Minchan Kim > --- > mm/page_alloc.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 266f267..019c4fe 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -5496,7 +5496,11 @@ __count_immobile_pages(struct zone *zone, struct page *page, int count) > continue; > > page = pfn_to_page(check); > - if (!page_count(page)) { > + /* > + * We can't use page_count withou pin a page > + * because another CPU can free compound page. > + */ > + if (!atomic_read(&page->_count)) { > if (PageBuddy(page)) > iter += (1<< page_order(page)) - 1; > continue; Nice Catch. Other than the comment fix already pointed out.. Hmm...BTW, it seems this __count_xxx doesn't have any code for THP/Hugepage.. so, we need more fixes for better code, I think. Hmm, Don't we need !PageTail() check and 'skip thp' code ? Thanks, -Kame -- 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/