Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751572AbaBEImj (ORCPT ); Wed, 5 Feb 2014 03:42:39 -0500 Received: from cantor2.suse.de ([195.135.220.15]:44949 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750799AbaBEImh (ORCPT ); Wed, 5 Feb 2014 03:42:37 -0500 Date: Wed, 5 Feb 2014 09:42:35 +0100 From: Michal Hocko To: David Rientjes Cc: Andrew Morton , Holger Kiehl , Christoph Lameter , Rafael Aquini , Vlastimil Babka , Mel Gorman , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [patch v2] mm, page_alloc: make first_page visible before PageTail Message-ID: <20140205084235.GA30705@dhcp22.suse.cz> References: <20140203122052.GC2495@dhcp22.suse.cz> <20140203162036.GJ2495@dhcp22.suse.cz> <52EFC93D.3030106@suse.cz> <20140204160641.8f5d369eeb2d0318618d6d5f@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 On Tue 04-02-14 16:22:53, David Rientjes wrote: > Commit bf6bddf1924e ("mm: introduce compaction and migration for ballooned > pages") introduces page_count(page) into memory compaction which > dereferences page->first_page if PageTail(page). > > Introduce a store memory barrier to ensure page->first_page is properly > initialized so that code that does page_count(page) on pages off the lru > always have a valid p->first_page. > > Reported-by: Holger Kiehl > Signed-off-by: David Rientjes > --- > v2: with commentary, per checkpatch > > mm/page_alloc.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -369,9 +369,11 @@ void prep_compound_page(struct page *page, unsigned long order) > __SetPageHead(page); > for (i = 1; i < nr_pages; i++) { > struct page *p = page + i; > - __SetPageTail(p); > set_page_count(p, 0); > p->first_page = page; > + /* Make sure p->first_page is always valid for PageTail() */ > + smp_wmb(); > + __SetPageTail(p); Where is the pairing smp_rmb? I would expect it in comound_head. > } > } > -- 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/