On Wed, Mar 05 2008 at 2:26 +0200, FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx> wrote: > On Wed, 05 Mar 2008 08:33:05 +0900 > Tejun Heo <htejun@xxxxxxxxx> 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 <bharrosh@xxxxxxxxxxx> 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 <bharrosh@xxxxxxxxxxx> Signed-off-by: Benny Halevy <bhalevy@xxxxxxxxxxx> --- 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)); /* * 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-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html