Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933608AbYCEMtX (ORCPT ); Wed, 5 Mar 2008 07:49:23 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759479AbYCEMtD (ORCPT ); Wed, 5 Mar 2008 07:49:03 -0500 Received: from brick.kernel.dk ([87.55.233.238]:10144 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757397AbYCEMtA (ORCPT ); Wed, 5 Mar 2008 07:49:00 -0500 Date: Wed, 5 Mar 2008 13:48:57 +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: <20080305124857.GJ6704@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> <20080305123317.GI6704@kernel.dk> <47CE9634.6040501@panasas.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <47CE9634.6040501@panasas.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5441 Lines: 120 On Wed, Mar 05 2008, Boaz Harrosh wrote: > On Wed, Mar 05 2008 at 14:33 +0200, Jens Axboe wrote: > > 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. > > > Updated, you are absolutely right, thanks. > > Will you commit below patch for 2.6.25? I know that, at the time, I have > seen this scsi-ml-loop in action on a sata drive here in the lab, on an > x86_64 machine. The current solution will silently corrupt data, which > is very hard to find. Yes, was just hoping you'd resend with the above corrected, so thanks! I'll add it to the pending queue for 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/