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

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Date:   Wed,  7 Dec 2016 23:38:33 -0500
From:   Jérémy Lefaure 
        <jeremy.lefaure@....epita.fr>
To:     x86@...nel.org, Borislav Petkov <bp@...e.de>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org,
        Jérémy Lefaure 
        <jeremy.lefaure@....epita.fr>
Subject: [PATCH] x86/vm86: fix compilation warning on a unused variable

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);
 		split_huge_pmd(vma, pmd, 0xA0000);
 	}
 	if (pmd_none_or_clear_bad(pmd))
-- 
2.10.2