From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx146.postini.com [74.125.245.146]) by kanga.kvack.org (Postfix) with SMTP id 0D5236B0044 for ; Tue, 1 May 2012 10:37:41 -0400 (EDT) Received: by ghrr18 with SMTP id r18so2644131ghr.14 for ; Tue, 01 May 2012 07:37:41 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: References: <1335778207-6511-1-git-send-email-jack@suse.cz> From: KOSAKI Motohiro Date: Tue, 1 May 2012 10:37:20 -0400 Message-ID: Subject: Re: [PATCH] Describe race of direct read and fork for unaligned buffers Content-Type: text/plain; charset=ISO-8859-1 Sender: owner-linux-mm@kvack.org List-ID: To: Jan Kara Cc: Michael Kerrisk , LKML , linux-man@vger.kernel.org, linux-mm@kvack.org, mgorman@suse.de, Jeff Moyer , npiggin@gmail.com > Hello, > > Thank you revisit this. But as far as my remember is correct, this issue is NOT > unaligned access issue. It's just get_user_pages(_fast) vs fork race issue. i.e. > DIRECT_IO w/ multi thread process should not use fork(). The problem is, fork (and its COW logic) assume new access makes cow break, But page table protection can't detect a DMA write. Therefore DIO may override shared page data. -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org