Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933717AbYCEMdj (ORCPT ); Wed, 5 Mar 2008 07:33:39 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754294AbYCEMdX (ORCPT ); Wed, 5 Mar 2008 07:33:23 -0500 Received: from brick.kernel.dk ([87.55.233.238]:12637 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753691AbYCEMdV (ORCPT ); Wed, 5 Mar 2008 07:33:21 -0500 Date: Wed, 5 Mar 2008 13:33:18 +0100 From: Jens Axboe To: Boaz Harrosh Cc: FUJITA Tomonori , Tejun Heo , Mike Galbraith , James.Bottomley@HansenPartnership.com, tomof@acm.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-ide@vger.kernel.org, linux-scsi@vger.kernel.org, jgarzik@pobox.com, bzolnier@gmail.com Subject: Re: [PATCH] blk: missing add of padded bytes to io completion byte count Message-ID: <20080305123317.GI6704@kernel.dk> References: <47CD7C05.1080707@gmail.com> <20080305041914V.tomof@acm.org> <47CDDC31.4070806@gmail.com> <20080305092619Y.fujita.tomonori@lab.ntt.co.jp> <47CE72EF.7050302@panasas.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <47CE72EF.7050302@panasas.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4661 Lines: 112 On Wed, Mar 05 2008, Boaz Harrosh wrote: > On Wed, Mar 05 2008 at 2:26 +0200, FUJITA Tomonori wrote: > > On Wed, 05 Mar 2008 08:33:05 +0900 > > Tejun Heo wrote: > > > >> FUJITA Tomonori wrote: > >>> Hmm, does SCSI mid-layer need to care about how many bytes the block > >>> layer allocates? I don't think that extra_len is NOT good_bytes. > >>> > >>> I think that the block layer had better take care about it (fix > >>> __end_that_request_first?). > >> Yeah, probably calling completion functions w/o bytes count is the right > >> thing to do but what I was talking about was what could break when the > >> semantics of rq->data_len changed. If we keep rq->data_len() == > >> sum(sg), we keep it business as usual for all the rest except for the > >> device application layer if we don't we do the reverse and SCSI midlayer > >> completion was a good example, I think. > > > > sglist is a low-level I/O representation for device drivers. SCSI > > midlayer should not care about sglist. We should not fix SCSI midlayer > > for rq->data_len != sum(sg) change (so I can't agree with your > > diagrams in another mail). > > > > When if we change a rule, we need to fix something. > > > > If we keep rq->data_len == sum(sg), we need to fix the device > > application layer. If we keep rq->data_len == the true data length, we > > need to fix the low-level drivers. > > > > Now I'm fine with the commit e97a294ef6938512b655b1abf17656cf2b26f709 > > since we are in -rc stages. But I plan to send a patch to revert it > > and fix this issue in the block layer. I'd like to test it in -mm for > > a while. > > No this commit is a serious bug, and the only fix is like you suggested > in __end_that_request_first. This is because it breaks that scsi-ml loop > where scsi_bufflen() can be less then blk_rq_bytes(). In that case this > commit is a data corruption. > > > Only sglist stuff in SCSI midlayer is scsi_req_map_sg now. As you > > know, we really want to remove it. > > > > > >> Things going the other way is fine with me but I at least want to hear a > >> valid rationale. Till now all I got is "because that's the true size" > >> which doesn't really make much sense to me. > > > > Most of users of request structure care about only the real data > > length, don't care about padding and drain length. Why do they bother > > to use a helper function to get the real data length? > > -- > > Submitted is the right fix to this problem, as pointed out by TOMO. > Please test it solves the CD burning problem. > (The patch includes the revert of commit e97a294e) > --- > From: Boaz Harrosh > Date: Wed, 5 Mar 2008 12:07:12 +0200 > Subject: [PATCH] blk: missing add of padded bytes to io completion byte count > > the commit e97a294ef6938512b655b1abf17656cf2b26f709 was very wrong. This is > because scsi-ml supports the ability to split a request into smaller chunks, > in which case scsi_bufflen() is smaller then request length. Then at completion > time the remainder can be issued as a new scsi command. In that case the above > commit is a data corruption. We needed something for -rc4, so it had to be rushed a bit... > Also in this fix all users of block layer are taken care of, and not only > scsi devices. > > Signed-off-by: Boaz Harrosh > Signed-off-by: Benny Halevy > --- > block/blk-core.c | 4 ++++ > drivers/scsi/scsi.c | 2 +- > 2 files changed, 5 insertions(+), 1 deletions(-) > > diff --git a/block/blk-core.c b/block/blk-core.c > index 2a438a9..37fcccc 100644 > --- a/block/blk-core.c > +++ b/block/blk-core.c > @@ -1549,6 +1549,9 @@ static int __end_that_request_first(struct request *req, int error, > nr_bytes >> 9, req->sector); > } > > + if (nr_bytes >= blk_rq_bytes(req)) > + nr_bytes += req->extra_len; > + > total_bytes = bio_nbytes = 0; > while ((bio = req->bio) != NULL) { > int nbytes; > @@ -1616,6 +1619,7 @@ static int __end_that_request_first(struct request *req, int error, > if (!req->bio) > return 0; > > + BUG_ON(total_bytes >= blk_rq_bytes(req)); Make that a WARN_ON() first please. It's indeed a bug, but it wont be critical and it's not fair killing everything since this padding stuff is so fresh and may still need a tweak or two. I'd be fine with making it a BUG_ON() post 2.6.25. -- Jens Axboe -- 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/