Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757383Ab3CSA5T (ORCPT ); Mon, 18 Mar 2013 20:57:19 -0400 Received: from mx1.redhat.com ([209.132.183.28]:18917 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754429Ab3CSA5S (ORCPT ); Mon, 18 Mar 2013 20:57:18 -0400 Date: Tue, 19 Mar 2013 08:56:59 +0800 From: Asias He To: Ben Hutchings Cc: "Nicholas A. Bellinger" , linux-kernel@vger.kernel.org, stable@vger.kernel.org, Greg Kroah-Hartman , target-devel Subject: Re: [ 04/21] target/pscsi: Fix page increment Message-ID: <20130319005659.GB15879@hj.localdomain> References: <20130312223245.109098379@linuxfoundation.org> <20130312223245.664885170@linuxfoundation.org> <1363399822.3937.161.camel@deadeye.wl.decadent.org.uk> <20130318053519.GE6232@hj.localdomain> <1363640434.3156.36.camel@haakon2.linux-iscsi.org> <1363649447.3937.348.camel@deadeye.wl.decadent.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1363649447.3937.348.camel@deadeye.wl.decadent.org.uk> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3852 Lines: 107 On Mon, Mar 18, 2013 at 11:30:47PM +0000, Ben Hutchings wrote: > On Mon, 2013-03-18 at 14:00 -0700, Nicholas A. Bellinger wrote: > > 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 page is set using sg_page() in the outer loop and was then > incremented in the inner loop. > > for_each_sg(sgl, sg, sgl_nents, i) { > page = sg_page(sg); > off = sg->offset; > len = sg->length; > > while (len > 0 && data_len > 0) { > bytes = min_t(unsigned int, len, PAGE_SIZE - off); > bytes = min(bytes, data_len); > ... > /* page++; */ > len -= bytes; > data_len -= bytes; > off = 0; > } > } > > The inner loop is apparently meant to iterate over pages of a segment, > but is now just wrapping around a single page. Yes, but we never loop more than once in the inner loop. So, how about 1) fail on sg->offset + sg->length > PAGE_SIZE (we can not find a proper page address in this case) 2) remove the inner while loop, run the code was in the loop only once. > > The case where this logic is broken, and that the 'page > > ++' was addressing is when sg->length > PAGE_SIZE. > > That is a sufficient but not a necessary condition for the increment. > > Ben. > > -- > Ben Hutchings > Never attribute to conspiracy what can adequately be explained by stupidity. -- Asias -- 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/