linux-kernel - Re: Write barriers on MD RAID1

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Message-ID: <19009.61911.914777.973086@notabene.brown>
Date:	Wed, 24 Jun 2009 19:28:55 +1000
From:	Neil Brown <neilb@...e.de>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Ken Milmore <ken.milmore@...glemail.com>,
	linux-kernel@...r.kernel.org, linux-raid@...r.kernel.org,
	dm-devel@...hat.com
Subject: Re: Write barriers on MD RAID1

On Wednesday June 24, jens.axboe@...cle.com wrote:
> On Wed, Jun 24 2009, Neil Brown wrote:
> > On Sunday June 21, ken.milmore@...glemail.com wrote:
> > > I thought I had better bump my previous post as this regression is still 
> > > present in 2.6.29.5.
> > 
> > Thanks Ken.
> > 
> > > 
> > > To recap, commit cec0707e40ae25794b5a2de7b7f03c51961f80d9 has broken 
> > > write barriers on md raid1 block devices in 2.6.29 and later kernels. 
> > > Reversing this commit appears to fix the problem.
> > > 
> > > Please let me know if I'm harassing the wrong maintainers here!
> > 
> > Jens,
> >   have you had a chance to look at this?
> 
> Yeah, I think it's the right way to go. I'll queue it up for .31 and we
> should put in in -stable as well.

Great, thanks.

NeilBrown


> 
> > 
> > I think the following patch is appropriate and should go in to
> > -stable.
> > 
> > Thanks,
> > NeilBrown
> > 
> > 
> > From addd8b129835a63d6df9a38eae20caaa15de5988 Mon Sep 17 00:00:00 2001
> > From: NeilBrown <neilb@...e.de>
> > Date: Wed, 24 Jun 2009 13:39:15 +1000
> > Subject: [PATCH] Restore barrier support for md and probably other virtual devices.
> > 
> > The next_ordered flag is only meaningful for devices that use __make_request.
> > So move the test against next_ordered out of generic code and in to
> > __make_request
> > 
> > Since this test was added, barriers have not worked on md, and (I
> > think) dm and similar devices that don't use __make_request and so
> > don't bother to set next_ordered.
> > 
> > Cc: stable@...nel.org
> > Cc: Ken Milmore <ken.milmore@...glemail.com>
> > Signed-off-by: NeilBrown <neilb@...e.de>
> > ---
> >  block/blk-core.c |   10 +++++-----
> >  1 files changed, 5 insertions(+), 5 deletions(-)
> > 
> > diff --git a/block/blk-core.c b/block/blk-core.c
> > index b06cf5c..fc221aa 100644
> > --- a/block/blk-core.c
> > +++ b/block/blk-core.c
> > @@ -1172,6 +1172,11 @@ static int __make_request(struct request_queue *q, struct bio *bio)
> >  	const int unplug = bio_unplug(bio);
> >  	int rw_flags;
> >  
> > +	if (bio_barrier(bio) && bio_has_data(bio) &&
> > +	    (q->next_ordered == QUEUE_ORDERED_NONE)) {
> > +		bio_endio(bio, -EOPNOTSUPP)
> > +			return 0;
> > +	}
> >  	/*
> >  	 * low level driver can indicate that it wants pages above a
> >  	 * certain limit bounced to low memory (ie for highmem, or even
> > @@ -1472,11 +1477,6 @@ 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);
> > -- 
> > 1.6.3.1
> > 
> 
> -- 
> Jens Axboe
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