linux-kernel - Re: [PATCH 2/2] block: Avoid deadlocks with bio allocation by stacking drivers

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Date:	Mon, 10 Sep 2012 14:33:49 -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, axboe@...nel.dk,
	Vivek Goyal <vgoyal@...hat.com>,
	Mikulas Patocka <mpatocka@...hat.com>, bharrosh@...asas.com,
	david@...morbit.com
Subject: Re: [PATCH 2/2] block: Avoid deadlocks with bio allocation by
 stacking drivers

On Mon, Sep 10, 2012 at 01:40:10PM -0700, Tejun Heo wrote:
> Hello, Kent.
> 
> On Mon, Sep 10, 2012 at 01:24:35PM -0700, Kent Overstreet wrote:
> > And at that point, why duplicate that line of code? It doesn't matter that
> > much, but IMO a goto retry better labels what's actually going on (it's
> > something that's not uncommon in the kernel and if I see a retry label
> > in a function I pretty immediately have an idea of what's going on).
> > 
> > So we could do
> > 
> > retry:
> > p = mempool_alloc(bs->bio_pool, gfp_mask);
> > if (!p && gfp_mask != saved_gfp) {
> > 	punt_bios_to_rescuer(bs);
> > 	gfp_mask = saved_gfp;
> > 	goto retry;
> > }
> 
> Yes, we do retry loops if that makes the code simpler.  Doing that to
> save one extra alloc call, I don't think so.

"Simpler" isn't really an objective thing though. To me the goto version
is more obvious/idiomatic.

Eh. I'll do it your way, but consider this a formal objection :p
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