From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx192.postini.com [74.125.245.192]) by kanga.kvack.org (Postfix) with SMTP id B30126B0039 for ; Tue, 2 Apr 2013 15:30:36 -0400 (EDT) Received: by mail-pb0-f50.google.com with SMTP id jt11so416159pbb.37 for ; Tue, 02 Apr 2013 12:30:36 -0700 (PDT) Date: Tue, 2 Apr 2013 12:30:15 -0700 (PDT) From: Hugh Dickins 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> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Minchan Kim Cc: David Rientjes , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Mel Gorman , Andrea Arcangeli , Kamezawa Hiroyuki 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, 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