linux-kernel - Re: [PATCH 04/13] block: Add bio_clone

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Message-ID: <20120518203932.GD9673@google.com>
Date:	Fri, 18 May 2012 13:39:32 -0700
From:	Kent Overstreet <koverstreet@...gle.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	linux-bcache@...r.kernel.org, linux-kernel@...r.kernel.org,
	dm-devel@...hat.com, linux-fsdevel@...r.kernel.org,
	axboe@...nel.dk, agk@...hat.com, neilb@...e.de,
	yehuda@...newdream.net, sage@...dream.net
Subject: Re: [PATCH 04/13] block: Add bio_clone_kmalloc()

On Fri, May 18, 2012 at 09:09:03AM -0700, Tejun Heo wrote:
> On Thu, May 17, 2012 at 10:59:51PM -0400, koverstreet@...gle.com wrote:
> > @@ -729,7 +729,7 @@ static struct bio *bio_chain_clone(struct bio **old, struct bio **next,
> >  	}
> >  
> >  	while (old_chain && (total < len)) {
> > -		tmp = bio_kmalloc(gfpmask, old_chain->bi_max_vecs);
> > +		tmp = bio_clone_kmalloc(old_chain, gfpmask);
> >  		if (!tmp)
> >  			goto err_out;
> >  
> > @@ -751,13 +751,9 @@ static struct bio *bio_chain_clone(struct bio **old, struct bio **next,
> >  			if (!bp)
> >  				goto err_out;
> >  
> > -			__bio_clone(tmp, &bp->bio1);
> > -
> 
> This effectively swaps the order of bio_split() and __bio_clone().  Is
> that safe?  Also, please cc the maintainer.

Now that I look at that code some more, I'm not sure it was quite right
before - that or I don't follow how it's supposed to work.

That bio_split() effectively does its own clone, so it seems to me the
bio_kmalloc()/bio_clone_kmalloc() should only be happening in the non
split case.

Also, there's a bio_chain_clone in drivers/block/osdblk.c that looks
like it's doing something similar, probably we should have some generic
code for this.
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