linux-kernel - Re: [PATCH] mm, hugetlb: move the error handle logic out of normal code path

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Message-Id: <20140515153620.344fe054b6b8d054a28fbf82@linux-foundation.org>
Date:	Thu, 15 May 2014 15:36:20 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	Jianyu Zhan <nasa4836@...il.com>, iamjoonsoo.kim@....com,
	aneesh.kumar@...ux.vnet.ibm.com, n-horiguchi@...jp.nec.com,
	aarcange@...hat.com, steve.capper@...aro.org, davidlohr@...com,
	kirill.shutemov@...ux.intel.com, dave.hansen@...ux.intel.com,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm, hugetlb: move the error handle logic out of normal
 code path

On Thu, 15 May 2014 11:01:42 +0200 Michal Hocko <mhocko@...e.cz> wrote:

> On Wed 14-05-14 15:10:59, Jianyu Zhan wrote:
> > alloc_huge_page() now mixes normal code path with error handle logic.
> > This patches move out the error handle logic, to make normal code
> > path more clean and redue code duplicate.
> 
> I don't know. Part of the function returns and cleans up on its own and
> other part relies on clean up labels. This is not so much nicer than the
> previous state.

That's actually a common pattern:

foo()
{
	if (check which doesn't change any state)
		return -Efoo;
	if (another check which doesn't change any state)
		return -Ebar;

	do_something_which_changes_state()
	
	if (another check)
		goto undo_that_state_chage;
	...

undo_that_state_change:
	...
}


This ties into the main reason why we use all these gotos: to support
evolution of the code.  With multiple return points we risk later
adding resource leaks and locking errors.  Plus the code becomes more
and more duplicative and spaghettified.


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