linux-kernel - Re: arch/sparc/mm/srmmu.c:300:9: error: variable 'pud' set but not used

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Date:   Wed, 20 May 2020 16:20:05 +0300
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     kbuild test robot <lkp@...el.com>
Cc:     kbuild-all@...ts.01.org, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Memory Management List <linux-mm@...ck.org>
Subject: Re: arch/sparc/mm/srmmu.c:300:9: error: variable 'pud' set but not
 used

On Wed, May 20, 2020 at 08:57:33AM +0800, kbuild test robot wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   642b151f45dd54809ea00ecd3976a56c1ec9b53d
> commit: 7235db268a2777bc380b99b7db49ff7b19c8fb76 sparc32: use pgtable-nopud instead of 4level-fixup
> config: sparc-defconfig (attached as .config)
> compiler: sparc-linux-gcc (GCC) 9.3.0
> reproduce:
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         git checkout 7235db268a2777bc380b99b7db49ff7b19c8fb76
>         # save the attached .config to linux build tree
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=sparc
> 
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kbuild test robot <lkp@...el.com>
> 
> All errors (new ones prefixed by >>, old ones prefixed by <<):
> 
> arch/sparc/mm/srmmu.c: In function 'srmmu_nocache_init':
> >> arch/sparc/mm/srmmu.c:300:9: error: variable 'pud' set but not used [-Werror=unused-but-set-variable]
> 300 |  pud_t *pud;
> |         ^~~

Here's the fix vs v5.7-rc6-mmots-2020-05-19-21-52:

>From 192848144e61e3ebacd34598386e4fa773d19ae9 Mon Sep 17 00:00:00 2001
From: Mike Rapoport <rppt@...ux.ibm.com>
Date: Wed, 20 May 2020 15:39:22 +0300
Subject: [PATCH] sparc32: use PUD rather than PGD to get PMD in
 srmmu_nocache_init()

The kbuild test robot reported the following warning:

arch/sparc/mm/srmmu.c: In function 'srmmu_nocache_init':
>> arch/sparc/mm/srmmu.c:300:9: error: variable 'pud' set but not used
>> [-Werror=unused-but-set-variable]
300 |  pud_t *pud;

This warning is caused by misprint in the page table traversal in
srmmu_nocache_init() function which accessed a PMD entry using PGD rather
than PUD.
Since sparc32 has only 3 page table levels, the PGD and PUD are essentially
the same and usage of __nocache_fix() removed the type checking.

Use PUD for the consistency and to silence the compiler warning.

Reported-by: kbuild test robot <lkp@...el.com>
Signed-off-by: Mike Rapoport <rppt@...ux.ibm.com>
---
 arch/sparc/mm/srmmu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/sparc/mm/srmmu.c b/arch/sparc/mm/srmmu.c
index 6cb1ea2d2b5c..75b56bdd38ef 100644
--- a/arch/sparc/mm/srmmu.c
+++ b/arch/sparc/mm/srmmu.c
@@ -304,7 +304,7 @@ static void __init srmmu_nocache_init(void)
 		pgd = pgd_offset_k(vaddr);
 		p4d = p4d_offset(__nocache_fix(pgd), vaddr);
 		pud = pud_offset(__nocache_fix(p4d), vaddr);
-		pmd = pmd_offset(__nocache_fix(pgd), vaddr);
+		pmd = pmd_offset(__nocache_fix(pud), vaddr);
 		pte = pte_offset_kernel(__nocache_fix(pmd), vaddr);
 
 		pteval = ((paddr >> 4) | SRMMU_ET_PTE | SRMMU_PRIV);
-- 
2.26.2