linux-kernel - Re: new barrier warnings in 2.6.29-rc1

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Date:	Tue, 13 Jan 2009 11:45:24 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Christoph Hellwig <hch@....de>, linux-kernel@...r.kernel.org
Subject: Re: new barrier warnings in 2.6.29-rc1

On Tue, Jan 13 2009, Tejun Heo wrote:
> Hello, Jens.
> 
> Jens Axboe wrote:
> > On Tue, Jan 13 2009, Tejun Heo wrote:
> >> I think the right thing to do is setting REQ_QUIET on the trial
> >> barrier request.
> > 
> > It would surely work, but XFS doesn't really have a way to do that. Then
> > we would have to add a bio quiet flag and inherit that.
> > 
> > I kind of liked the old behaviour. What about something like the below?
> > 
> > diff --git a/block/blk-core.c b/block/blk-core.c
> > index a824e49..eddba4a 100644
> > --- a/block/blk-core.c
> > +++ b/block/blk-core.c
> > @@ -1448,6 +1448,11 @@ static inline void __generic_make_request(struct bio *bio)
> >  			err = -EOPNOTSUPP;
> >  			goto end_io;
> >  		}
> > +		if (bio_barrier(bio) && bio_has_data(bio) &&
> > +		    (q->next_ordered == QUEUE_ORDERED_NONE)) {
> > +			err = -EOPNOTSUPP;
> > +			goto end_io;
> > +		}
> >  
> >  		ret = q->make_request_fn(q, bio);
> >  	} while (ret);
> 
> I have no objection against it.  I kind of like having single test
> point but it's a corner case anyway so no biggie.

I agree, but it's a lot better than having to fiddle around with every
spot that wants to do a barrier probe. I'll merge it up for 2.6.29.
Christoph, can you double check that it gets rid of your warning and
still catches the barrier disable?

-- 
Jens Axboe

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