Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932789AbYCEMxn (ORCPT ); Wed, 5 Mar 2008 07:53:43 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759632AbYCEMxa (ORCPT ); Wed, 5 Mar 2008 07:53:30 -0500 Received: from bzq-219-195-70.pop.bezeqint.net ([62.219.195.70]:35008 "EHLO bh-buildlin2.bhalevy.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751140AbYCEMx3 (ORCPT ); Wed, 5 Mar 2008 07:53:29 -0500 Message-ID: <47CE9634.6040501@panasas.com> Date: Wed, 05 Mar 2008 14:46:44 +0200 From: Boaz Harrosh User-Agent: Thunderbird 2.0.0.9 (X11/20071031) MIME-Version: 1.0 To: Jens Axboe 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 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> In-Reply-To: <20080305123317.GI6704@kernel.dk> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7021 Lines: 173 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. Boaz --- 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. 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..c82e68a 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; + WARN_ON(total_bytes >= blk_rq_bytes(req)); /* * if the request wasn't completed, update state */ diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c index e5c6f6a..fecba05 100644 --- a/drivers/scsi/scsi.c +++ b/drivers/scsi/scsi.c @@ -757,7 +757,7 @@ void scsi_finish_command(struct scsi_cmnd *cmd) "Notifying upper driver of completion " "(result %x)\n", cmd->result)); - good_bytes = scsi_bufflen(cmd) + cmd->request->extra_len; + good_bytes = scsi_bufflen(cmd); if (cmd->request->cmd_type != REQ_TYPE_BLOCK_PC) { drv = scsi_cmd_to_driver(cmd); if (drv->done) -- 1.5.3.3 -- 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/