Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754869Ab3CRVAj (ORCPT ); Mon, 18 Mar 2013 17:00:39 -0400 Received: from mail.linux-iscsi.org ([67.23.28.174]:58354 "EHLO linux-iscsi.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754539Ab3CRVAh (ORCPT ); Mon, 18 Mar 2013 17:00:37 -0400 Subject: Re: [ 04/21] target/pscsi: Fix page increment From: "Nicholas A. Bellinger" To: Asias He Cc: Ben Hutchings , linux-kernel@vger.kernel.org, stable@vger.kernel.org, Greg Kroah-Hartman , target-devel In-Reply-To: <20130318053519.GE6232@hj.localdomain> References: <20130312223245.109098379@linuxfoundation.org> <20130312223245.664885170@linuxfoundation.org> <1363399822.3937.161.camel@deadeye.wl.decadent.org.uk> <20130318053519.GE6232@hj.localdomain> Content-Type: text/plain; charset="UTF-8" Date: Mon, 18 Mar 2013 14:00:34 -0700 Message-ID: <1363640434.3156.36.camel@haakon2.linux-iscsi.org> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2486 Lines: 66 On Mon, 2013-03-18 at 13:35 +0800, Asias He wrote: > On Sat, Mar 16, 2013 at 02:10:22AM +0000, Ben Hutchings wrote: > > On Tue, 2013-03-12 at 15:44 -0700, Greg Kroah-Hartman wrote: > > > 3.0-stable review patch. If anyone has any objections, please let me know. > > > > > > ------------------ > > > > > > From: Asias He > > > > > > commit 472b72f2db7831d7dbe22ffdff4adee3bd49b05d upstream. > > > > > > The page++ is wrong. It makes bio_add_pc_page() pointing to a wrong page > > > address if the 'while (len > 0 && data_len > 0) { ... }' loop is > > > executed more than one once. > > > > > > Signed-off-by: Asias He > > > Signed-off-by: Nicholas Bellinger > > > Signed-off-by: Greg Kroah-Hartman > > > > > > --- > > > drivers/target/target_core_pscsi.c | 1 - > > > 1 file changed, 1 deletion(-) > > > > > > --- a/drivers/target/target_core_pscsi.c > > > +++ b/drivers/target/target_core_pscsi.c > > > @@ -1210,7 +1210,6 @@ static int __pscsi_map_task_SG( > > > bio = NULL; > > > } > > > > > > - page++; > > > len -= bytes; > > > data_len -= bytes; > > > off = 0; > > > > So in case a fragment crosses a page boundary, we wrap around to the > > beginning of the same page? That doesn't look right. > > If the fragment crosses a page boundary, what is the correct page > for it? > > Nicholas, can we assume sg->length + sg->offset should be less than PAGE_SIZE here? > sg->length + sg->offset can be less than or equal to PAGE_SIZE here. For everything other than tcm_loop + tcm_vhost using externally allocated SGLs, we can expect fragments to never cross the page boundary. For tcm_loop + tcm_vhost, there are a few special cases with control CDB paylaods (usually going through scsi-generic) where we can have a non zero sg->offset, but at least in the cases I've seen this is still not using SGL elements that exceed PAGE_SIZE. So, I think this logic is OK for SGLs that cross page boundries, given that it's done outside of the inner loop where *page is set during each for_each_sg(). The case where this logic is broken, and that the 'page ++' was addressing is when sg->length > PAGE_SIZE. --nab -- 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/