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Date: Mon, 17 Dec 2012 12:49:49 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Mel Gorman <mgorman@suse.de>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        kbuild test robot <fengguang.wu@intel.com>
Subject: Re: [PATCH] mm: Suppress mm/memory.o warning on older compilers if
 !CONFIG_NUMA_BALANCING
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On Mon, 17 Dec 2012 11:49:17 +0000
Mel Gorman <mgorman@suse.de> wrote:

> The kbuild test robot reported the following after the merge of Automatic
> NUMA Balancing when cross-compiling for avr32.
> 
> mm/memory.c: In function 'do_pmd_numa_page':
> mm/memory.c:3593: warning: no return statement in function returning non-void
> 
> The code is unreachable but the avr32 cross-compiler was not new enough
> to know that. This patch suppresses the warning.
> 
> Signed-off-by: Mel Gorman <mgorman@suse.de>
> ---
>  mm/memory.c |    1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index e6a3b93..23f1fdf 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3590,6 +3590,7 @@ static int do_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
>  		     unsigned long addr, pmd_t *pmdp)
>  {
>  	BUG();
> +	return 0;
>  }
>  #endif /* CONFIG_NUMA_BALANCING */

Odd.  avr32's BUG() includes a call to unreachable(), which should
evaluate to "do { } while (1)".  Can you check that this is working?

Perhaps it _is_ working, but the compiler incorrectly thinks that the
function can return?