linux-kernel - Re: + mm-mmapc-replace-find_vma_prepare-with-clearer-find_vma

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Date:	Tue, 11 Sep 2012 10:55:58 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	linux-kernel@...r.kernel.org
cc:	mm-commits@...r.kernel.org, hughd@...gle.com, bhalevy@...ian.com,
	dhillf@...il.com
Subject: Re: + mm-mmapc-replace-find_vma_prepare-with-clearer-find_vma_links.patch
 added to -mm tree

On Thu, 16 Aug 2012, akpm@...ux-foundation.org wrote:

> 
> The patch titled
>      Subject: mm/mmap.c: replace find_vma_prepare() with clearer find_vma_links()
> has been added to the -mm tree.  Its filename is
>      mm-mmapc-replace-find_vma_prepare-with-clearer-find_vma_links.patch
> 
> Before you just go and hit "reply", please:
>    a) Consider who else should be cc'ed
>    b) Prefer to cc a suitable mailing list as well
>    c) Ideally: find the original patch on the mailing list and do a
>       reply-to-all to that, adding suitable additional cc's
> 
> *** Remember to use Documentation/SubmitChecklist when testing your code ***
> 
> The -mm tree is included into linux-next and is updated
> there every 3-4 working days
> 
> ------------------------------------------------------
> From: Hugh Dickins <hughd@...gle.com>
> Subject: mm/mmap.c: replace find_vma_prepare() with clearer find_vma_links()
> 
> People get confused by find_vma_prepare(), because it doesn't care about
> what it returns in its output args, when its callers won't be interested.
> 
> Clarify by passing in end-of-range address too, and returning failure if
> any existing vma overlaps the new range: instead of returning an ambiguous
> vma which most callers then must check.  find_vma_links() is a clearer
> name.
> 
> This does revert 2.6.27's dfe195fb79e88 ("mm: fix uninitialized variables
> for find_vma_prepare callers"), but it looks like gcc 4.3.0 was one of
> those releases too eager to shout about uninitialized variables: only
> copy_vma() warns with 4.5.1 and 4.7.1, which a BUG on error silences.
> 

That trick doesn't work if CONFIG_BUG=n.

mm/mmap.c: In function 'copy_vma':
mm/mmap.c:2344: warning: 'prev' may be used uninitialized in this function
mm/mmap.c:2345: warning: 'rb_link' may be used uninitialized in this function
mm/mmap.c:2345: warning: 'rb_parent' may be used uninitialized in this function
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