From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx151.postini.com [74.125.245.151]) by kanga.kvack.org (Postfix) with SMTP id 2F3A46B006C for ; Sun, 10 Jun 2012 20:23:36 -0400 (EDT) Received: by dakp5 with SMTP id p5so5684269dak.14 for ; Sun, 10 Jun 2012 17:23:35 -0700 (PDT) Date: Mon, 11 Jun 2012 08:23:26 +0800 From: Wanpeng Li Subject: Re: [PATCH] mm: do not use page_count without a page pin Message-ID: <20120611002325.GA2384@kernel> Reply-To: Wanpeng Li References: <1339373872-31969-1-git-send-email-minchan@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1339373872-31969-1-git-send-email-minchan@kernel.org> Sender: owner-linux-mm@kvack.org List-ID: To: Minchan Kim Cc: Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrea Arcangeli , MelGorman , Michal Hocko , KAMEZAWA Hiroyuki On Mon, Jun 11, 2012 at 09:17:51AM +0900, 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 ^ without >+ * because another CPU can free compound page. >+ */ >+ if (!atomic_read(&page->_count)) { > if (PageBuddy(page)) > iter += (1 << page_order(page)) - 1; > continue; >-- >1.7.9.5 > >-- >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 -- 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