Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751138AbVJOMJ1 (ORCPT ); Sat, 15 Oct 2005 08:09:27 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751140AbVJOMJ1 (ORCPT ); Sat, 15 Oct 2005 08:09:27 -0400 Received: from 22.107.233.220.exetel.com.au ([220.233.107.22]:31506 "EHLO arnor.apana.org.au") by vger.kernel.org with ESMTP id S1751138AbVJOMJ1 (ORCPT ); Sat, 15 Oct 2005 08:09:27 -0400 From: Herbert Xu To: nickpiggin@yahoo.com.au (Nick Piggin) Subject: Re: Possible memory ordering bug in page reclaim? Cc: benh@kernel.crashing.org, hugh@veritas.com, paulus@samba.org, anton@samba.org, torvalds@osdl.org, akpm@osdl.org, andrea@suse.de, linux-kernel@vger.kernel.org Organization: Core In-Reply-To: <4350C4F6.4030807@yahoo.com.au> X-Newsgroups: apana.lists.os.linux.kernel User-Agent: tin/1.7.4-20040225 ("Benbecula") (UNIX) (Linux/2.4.27-hx-1-686-smp (i686)) Message-Id: Date: Sat, 15 Oct 2005 22:08:08 +1000 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1145 Lines: 28 Nick Piggin wrote: > > Well yes, that's on the store side (1, above). However can't a CPU > still speculatively (eg. guess the branch) load the page->flags > cacheline which might be satisfied from memory before the page->count > cacheline loads? Ie. you can still have the correct write ordering > but have incorrect read ordering? > > Because neither PageDirty nor page_count is a barrier, and there is > no read barrier between them. Yes you're right. A read barrier is required here. I think Ben was actually agreeing with you. He's just questioning whether the corresponding write barrier existed on CPU 1 (the answer to which is affirmative). Cheers, -- Visit Openswan at http://www.openswan.org/ Email: Herbert Xu ~{PmV>HI~} Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt - 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/