Re: [RFC] block: fix barrier error transmission

Jens Axboe
2008-04-03T08:06:32Z

On Wed, Apr 02 2008, James Bottomley wrote:
> On Wed, 2008-04-02 at 21:08 +0200, Jens Axboe wrote:
> > > diff --git a/block/blk-barrier.c b/block/blk-barrier.c
> > > index 55c5f1f..3a3947c 100644
> > > --- a/block/blk-barrier.c
> > > +++ b/block/blk-barrier.c
> > > @@ -114,18 +114,24 @@ void blk_ordered_complete_seq(struct request_queue *q, unsigned seq, int error)
> > >
> > > static void pre_flush_end_io(struct request *rq, int error)
> > > {
> > > + error = rq->errors ? -EIO : error;
> > > +
> > > elv_completed_request(rq->q, rq);
> > > blk_ordered_complete_seq(rq->q, QUEUE_ORDSEQ_PREFLUSH, error);
> > > }
> >
> > It's a bit of a hack, SCSI really should pass the error value back
> > instead of fiddling around with possibly perhaps finding it in ->errors.
> > And please don't use these ?: constructs, in this case it doesn't even
> > make a lot of sense and a
> >
> > if (rq->errors)
> > error = -EIO;
> >
> > would have been much cleaner ;-)
> >
> > So my question is why does the model not allow you to return the error
> > properly?
>
> I thought it was the sg_io that would be the problem, but apparently on
> further research, it simply discards the error as does scsi_execute_req.
>
> I suppose that's a strong enough reason to try returning an error ...
> I'm just a bit leery this close to a release.
>
> I think this will work ... it just really needs quite a bit of
> testing ...

This looks much better, but I'm with you on the danger of applying
something like this so close to a release...

Now, this isn't a regression, but it also impacts barrier reliability
and as such it's a big nasty to leave this open for another release.

>
> James
>
> ---
>
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index 1b199e1..67f412b 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -839,7 +839,7 @@ void scsi_io_completion(struct scsi_cmnd *cmd, unsigned int good_bytes)
> int this_count = scsi_bufflen(cmd);
> struct request_queue *q = cmd->device->request_queue;
> struct request *req = cmd->request;
> - int clear_errors = 1;
> + int error = 0;
> struct scsi_sense_hdr sshdr;
> int sense_valid = 0;
> int sense_deferred = 0;
> @@ -853,7 +853,6 @@ void scsi_io_completion(struct scsi_cmnd *cmd, unsigned int good_bytes)
> if (blk_pc_request(req)) { /* SG_IO ioctl from block level */
> req->errors = result;
> if (result) {
> - clear_errors = 0;
> if (sense_valid && req->sense) {
> /*
> * SG_IO wants current and deferred errors
> @@ -865,6 +864,8 @@ void scsi_io_completion(struct scsi_cmnd *cmd, unsigned int good_bytes)
> memcpy(req->sense, cmd->sense_buffer, len);
> req->sense_len = len;
> }
> + if (!sense_deferred)
> + error = -EIO;
> }
> if (scsi_bidi_cmnd(cmd)) {
> /* will also release_buffers */
> @@ -885,14 +886,11 @@ void scsi_io_completion(struct scsi_cmnd *cmd, unsigned int good_bytes)
> "%d bytes done.\n",
> req->nr_sectors, good_bytes));
>
> - if (clear_errors)
> - req->errors = 0;
> -
> /* A number of bytes were successfully read. If there
> * are leftovers and there is some kind of error
> * (result != 0), retry the rest.
> */
> - if (scsi_end_request(cmd, 0, good_bytes, result == 0) == NULL)
> + if (scsi_end_request(cmd, error, good_bytes, result == 0) == NULL)
> return;
>
> /* good_bytes = 0, or (inclusive) there were leftovers and
>
>

--
Jens Axboe