linux-kernel - Re: [PATCH] drivers/block/ub.c: use list_for_each

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Message-Id: <20070530163236.8bd5640c.zaitcev@redhat.com>
Date:	Wed, 30 May 2007 16:32:36 -0700
From:	Pete Zaitcev <zaitcev@...hat.com>
To:	Roland Dreier <rdreier@...co.com>
Cc:	"Satyam Sharma" <satyam.sharma@...il.com>,
	"Matthias Kaehlcke" <matthias.kaehlcke@...il.com>, axboe@...nel.dk,
	linux-usb-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: [PATCH] drivers/block/ub.c: use list_for_each_entry()

On Wed, 30 May 2007 16:14:01 -0700, Roland Dreier <rdreier@...co.com> wrote:

>  > The negative is the sheer number of helper functions in list.h. Personally,
>  > I find it difficult to retain a working knowledge of them. Iterators are
>  > particularly nasty that way. I'm thinking about dropping all of these
>  > list_for_each_with_murky_argument_requirements_and_odd_side_effects()
>  > and use plain for(;;), as a courtesy to someone who has to read the
>  > code years down the road.
> 
> I think I disagree with this reasoning.  If I'm reading your code and
> I see, say, list_for_each_entry_safe(), I can be pretty confident that
> your loop works correctly.  If you write your own for loop, then I
> have to check that you actually got the linked list walking right.

You have to check that I used list_for_each_entry_safe correctly too,
which is harder. Are you aware that we had (and probably still have)
dozens of cases where the use of list_for_each_entry_safe was buggy?
Most of them involved IHV programmers being lured into false sense
of security by the _safe suffix and getting their locking wrong.

You could not find a better way to blow up your own argument
than to mention list_for_each_entry_safe(), which is anything but.
Matthias' use of list_for_each_entry() actually IS safe, which is
why I am not NAKing it. Andrew has accepted it already. I just
think we aren't winning squat here.

-- Pete
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