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Old 12-11-2007, 09:46 PM
Kiyoshi Ueda
 
Default blk_end_request: changing ub (take 4)

This patch converts ub to use blk_end_request interfaces.
Related 'uptodate' arguments are converted to 'error'.

Cc: Pete Zaitcev <zaitcev@redhat.com>
Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
---
drivers/block/ub.c | 10 +++++-----
1 files changed, 5 insertions(+), 5 deletions(-)

Index: 2.6.24-rc4/drivers/block/ub.c
================================================== =================
--- 2.6.24-rc4.orig/drivers/block/ub.c
+++ 2.6.24-rc4/drivers/block/ub.c
@@ -808,16 +808,16 @@ static void ub_rw_cmd_done(struct ub_dev

static void ub_end_rq(struct request *rq, unsigned int scsi_status)
{
- int uptodate;
+ int error;

if (scsi_status == 0) {
- uptodate = 1;
+ error = 0;
} else {
- uptodate = 0;
+ error = -EIO;
rq->errors = scsi_status;
}
- end_that_request_first(rq, uptodate, rq->hard_nr_sectors);
- end_that_request_last(rq, uptodate);
+ if (__blk_end_request(rq, error, blk_rq_bytes(rq)))
+ BUG();
}

static int ub_rw_cmd_retry(struct ub_dev *sc, struct ub_lun *lun,

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Old 12-11-2007, 10:48 PM
Pete Zaitcev
 
Default blk_end_request: changing ub (take 4)

On Tue, 11 Dec 2007 17:46:47 -0500 (EST), Kiyoshi Ueda <k-ueda@ct.jp.nec.com> wrote:

> if (scsi_status == 0) {
> - uptodate = 1;
> + error = 0;
> } else {
> - uptodate = 0;
> + error = -EIO;
> rq->errors = scsi_status;
> }
> - end_that_request_first(rq, uptodate, rq->hard_nr_sectors);
> - end_that_request_last(rq, uptodate);
> + if (__blk_end_request(rq, error, blk_rq_bytes(rq)))
> + BUG();

Acked-by: Pete Zaitcev <zaitcev@redhat.com>

I follow the discussion, actually, and wanted to ask someone to look
closer if it's appropriate to use __blk_end_request() here.
My understanding was, blk_end_request() is the same thing, only
takes the queue lock. But then, should I refactor ub so that it
calls __blk_end_request if request function ends with an error
and blk_end_request if the end-of-IO even is processed? If not,
and the above is sufficient, why have blk_end_request at all?

-- Pete

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Old 12-12-2007, 07:38 PM
Kiyoshi Ueda
 
Default blk_end_request: changing ub (take 4)

Hi Pete,

On Tue, 11 Dec 2007 15:48:03 -0800, Pete Zaitcev <zaitcev@redhat.com> wrote:
> > if (scsi_status == 0) {
> > - uptodate = 1;
> > + error = 0;
> > } else {
> > - uptodate = 0;
> > + error = -EIO;
> > rq->errors = scsi_status;
> > }
> > - end_that_request_first(rq, uptodate, rq->hard_nr_sectors);
> > - end_that_request_last(rq, uptodate);
> > + if (__blk_end_request(rq, error, blk_rq_bytes(rq)))
> > + BUG();
>
> Acked-by: Pete Zaitcev <zaitcev@redhat.com>
>
> I follow the discussion, actually, and wanted to ask someone to look
> closer if it's appropriate to use __blk_end_request() here.
> My understanding was, blk_end_request() is the same thing, only
> takes the queue lock. But then, should I refactor ub so that it
> calls __blk_end_request if request function ends with an error
> and blk_end_request if the end-of-IO even is processed? If not,
> and the above is sufficient, why have blk_end_request at all?

The difference between blk_end_request() and __blk_end_request() is
whether the queue lock is held or not when end_that_request_last()
is called.
It's not relevant to the status of the request (error or not).

I'm using __blk_end_request() here and I think it's sufficient, because:
o end_that_request_last() must be called with the queue lock held
o ub_end_rq() calls end_that_request_last() without taking
the queue lock in itself.
So the queue lock must have been taken outside ub_end_rq().

But, if ub is calling end_that_request_last() without the queue lock,
it is a bug in the original code and we should use blk_end_request()
to fix that.

Does that answer satisfy you?

Thanks,
Kiyoshi Ueda

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Old 12-13-2007, 08:59 PM
Pete Zaitcev
 
Default blk_end_request: changing ub (take 4)

On Wed, 12 Dec 2007 15:38:15 -0500 (EST), Kiyoshi Ueda <k-ueda@ct.jp.nec.com> wrote:
> On Tue, 11 Dec 2007 15:48:03 -0800, Pete Zaitcev <zaitcev@redhat.com> wrote:

> > > - end_that_request_first(rq, uptodate, rq->hard_nr_sectors);
> > > - end_that_request_last(rq, uptodate);
> > > + if (__blk_end_request(rq, error, blk_rq_bytes(rq)))
> > > + BUG();

> > My understanding was, blk_end_request() is the same thing, only
> > takes the queue lock. But then, should I refactor ub so that it
> > calls __blk_end_request if request function ends with an error
> > and blk_end_request if the end-of-IO even is processed?

> I'm using __blk_end_request() here and I think it's sufficient, because:
> o end_that_request_last() must be called with the queue lock held
> o ub_end_rq() calls end_that_request_last() without taking
> the queue lock in itself.
> So the queue lock must have been taken outside ub_end_rq().

> But, if ub is calling end_that_request_last() without the queue lock,
> it is a bug in the original code and we should use blk_end_request()
> to fix that.

So, I have to rewrite ub to split the paths after all, right?
Let's do this then: I'll wait until your patch gets to Linus and
then update it with the split. The reason is, I need the whole
enchilada applied and I don't want to bother tracking iterations
and all the little segments (of which you already have 30).
Until then, ub will have a race by using your original small patch.

Best wishes,
-- Pete

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Old 12-14-2007, 04:04 PM
Kiyoshi Ueda
 
Default blk_end_request: changing ub (take 4)

Hi Pete,

On Thu, 13 Dec 2007 13:59:16 -0800, Pete Zaitcev <zaitcev@redhat.com> wrote:
> > > > - end_that_request_first(rq, uptodate, rq->hard_nr_sectors);
> > > > - end_that_request_last(rq, uptodate);
> > > > + if (__blk_end_request(rq, error, blk_rq_bytes(rq)))
> > > > + BUG();
> > >
> > > My understanding was, blk_end_request() is the same thing, only
> > > takes the queue lock. But then, should I refactor ub so that it
> > > calls __blk_end_request if request function ends with an error
> > > and blk_end_request if the end-of-IO even is processed?
> >
> > I'm using __blk_end_request() here and I think it's sufficient, because:
> > o end_that_request_last() must be called with the queue lock held
> > o ub_end_rq() calls end_that_request_last() without taking
> > the queue lock in itself.
> > So the queue lock must have been taken outside ub_end_rq().
> >
> > But, if ub is calling end_that_request_last() without the queue lock,
> > it is a bug in the original code and we should use blk_end_request()
> > to fix that.
>
> So, I have to rewrite ub to split the paths after all, right?
> Let's do this then: I'll wait until your patch gets to Linus and
> then update it with the split. The reason is, I need the whole
> enchilada applied and I don't want to bother tracking iterations
> and all the little segments (of which you already have 30).
> Until then, ub will have a race by using your original small patch.

No.
Are you doubting that the current ub code has the problem, aren't you?
My patch shouldn't introduce a NEW problem to ub.

I have investigated all code paths which call ub_end_rq() in ub.c,
and confirmed that ub_end_rq() is always called with the queue lock
held. (sc->lock is registered as a queue lock.)

So there is no such race in the current ub code.
You don't need to rewrite ub.

Thanks,
Kiyoshi Ueda

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Old 12-14-2007, 06:49 PM
Pete Zaitcev
 
Default blk_end_request: changing ub (take 4)

On Fri, 14 Dec 2007 12:04:54 -0500 (EST), Kiyoshi Ueda <k-ueda@ct.jp.nec.com> wrote:

> I have investigated all code paths which call ub_end_rq() in ub.c,
> and confirmed that ub_end_rq() is always called with the queue lock
> held. (sc->lock is registered as a queue lock.)

Thanks for reminding me about blk_init_queue, I forgot. Sorry for the
confusion.

Greetings,
-- Pete

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