linux-kernel - Re: [PATCH] x86/vm86: fix compilation warning on a unused variable

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Message-ID: <20161208083305.lczvpdi56xwac2gw@pd.tnic>
Date:   Thu, 8 Dec 2016 09:33:05 +0100
From:   Borislav Petkov <bp@...e.de>
To:     Jérémy Lefaure <jeremy.lefaure@....epita.fr>
Cc:     x86@...nel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/vm86: fix compilation warning on a unused variable

On Wed, Dec 07, 2016 at 11:38:33PM -0500, Jérémy Lefaure wrote:
> When CONFIG_TRANSPARENT_HUGEPAGE is disabled, split_huge_pmd is a no-op
> stub. In such case, vma is unused and a compiler raises a warning:
> 
> arch/x86/kernel/vm86_32.c: In function ‘mark_screen_rdonly’:
> arch/x86/kernel/vm86_32.c:180:26: warning: unused variable ‘vma’
> [-Wunused-variable]
>    struct vm_area_struct *vma = find_vma(mm, 0xA0000);
>                              ^~~
> Adding __maybe_unused in the vma declaration fixes this warning.
> 
> In addition, checking if CONFIG_TRANSPARENT_HUGEPAGE is enabled avoids
> calling find_vma function for nothing.
> 
> Signed-off-by: Jérémy Lefaure <jeremy.lefaure@....epita.fr>
> ---
>  arch/x86/kernel/vm86_32.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/vm86_32.c b/arch/x86/kernel/vm86_32.c
> index 01f30e5..0813b76 100644
> --- a/arch/x86/kernel/vm86_32.c
> +++ b/arch/x86/kernel/vm86_32.c
> @@ -176,8 +176,9 @@ static void mark_screen_rdonly(struct mm_struct *mm)
>  		goto out;
>  	pmd = pmd_offset(pud, 0xA0000);
>  
> -	if (pmd_trans_huge(*pmd)) {
> -		struct vm_area_struct *vma = find_vma(mm, 0xA0000);
> +	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && pmd_trans_huge(*pmd)) {
> +		struct vm_area_struct __maybe_unused *vma = find_vma(mm,
> +								     0xA0000);

So wouldn't the __maybe_unused alone without changing the if-condition
fix the warning too?

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--