Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932479Ab3DBTah (ORCPT ); Tue, 2 Apr 2013 15:30:37 -0400 Received: from mail-da0-f49.google.com ([209.85.210.49]:65042 "EHLO mail-da0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760406Ab3DBTag (ORCPT ); Tue, 2 Apr 2013 15:30:36 -0400 Date: Tue, 2 Apr 2013 12:30:15 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Minchan Kim cc: David Rientjes , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Mel Gorman , Andrea Arcangeli , Kamezawa Hiroyuki Subject: Re: [PATCH] THP: Use explicit memory barrier In-Reply-To: <20130402003746.GA30444@blaptop> Message-ID: References: <1364773535-26264-1-git-send-email-minchan@kernel.org> <20130402003746.GA30444@blaptop> User-Agent: Alpine 2.00 (LNX 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1706 Lines: 45 On Tue, 2 Apr 2013, Minchan Kim wrote: > On Mon, Apr 01, 2013 at 04:35:38PM -0700, David Rientjes wrote: > > On Mon, 1 Apr 2013, Minchan Kim wrote: > > > > > __do_huge_pmd_anonymous_page depends on page_add_new_anon_rmap's > > > spinlock for making sure that clear_huge_page write become visible > > > after set set_pmd_at() write. > > > > > > But lru_cache_add_lru uses pagevec so it could miss spinlock > > > easily so above rule was broken so user may see inconsistent data. > > > > > > This patch fixes it with using explict barrier rather than depending > > > on lru spinlock. > > > > > > > Is this the same issue that Andrea responded to in the "thp and memory > > barrier assumptions" thread at http://marc.info/?t=134333512700004 ? > > Yes and Peter pointed out further step. > Thanks for pointing out. > Not that I know that Andrea alreay noticed it, I don't care about this > patch. > > Remaining question is Kame's one. > > Hmm...how about do_anonymous_page() ? there are no comments/locks/barriers. > > Users can see non-zero value after page fault in theory ? > Isn't there anyone could answer it? See Nick's 2008 0ed361dec "mm: fix PageUptodate data race", which gave us static inline void __SetPageUptodate(struct page *page) { smp_wmb(); __set_bit(PG_uptodate, &(page)->flags); } So both do_anonymous_page() and __do_huge_pmd_anonymous_page() look safe to me already, though the huge_memory one could do with a fixed comment. Hugh -- 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/