linux-kernel - Re: [PATCH 12/30] blk_end_request: changing ub (take 4)

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Date:	Thu, 13 Dec 2007 13:59:16 -0800
From:	Pete Zaitcev <zaitcev@...hat.com>
To:	Kiyoshi Ueda <k-ueda@...jp.nec.com>
Cc:	jens.axboe@...cle.com, linux-kernel@...r.kernel.org,
	linux-scsi@...r.kernel.org, linux-ide@...r.kernel.org,
	dm-devel@...hat.com, j-nomura@...jp.nec.com, zaitcev@...hat.com
Subject: Re: [PATCH 12/30] blk_end_request: changing ub (take 4)

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