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

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Message-ID: <alpine.LSU.2.00.1209111110330.2575@eggly.anvils>
Date:	Tue, 11 Sep 2012 11:24:41 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	David Rientjes <rientjes@...gle.com>
cc:	linux-kernel@...r.kernel.org, mm-commits@...r.kernel.org,
	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 Tue, 11 Sep 2012, David Rientjes wrote:
> On Thu, 16 Aug 2012, akpm@...ux-foundation.org wrote:
> > 
> > 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

Hmm, right: not an option I ever choose, and I hadn't given it a thought.

But do we care?  If this introduced the only such warning, I would care.
But that seems to be far from the case - building my usual config without
CONFIG_BUG gives me 36 warnings, of uninitialized and unused and
control reaches end of non-void varieties.

Hugh
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