linux-kernel - Re: [PATCH V2 7/7] mm: Use pgdp_get() for accessing PGD entries

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Message-ID: <8f43251a-5418-4c54-a9b0-29a6e9edd879@arm.com>
Date: Thu, 19 Sep 2024 13:25:08 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: kernel test robot <lkp@...el.com>, linux-mm@...ck.org,
 "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: llvm@...ts.linux.dev, oe-kbuild-all@...ts.linux.dev,
 Andrew Morton <akpm@...ux-foundation.org>,
 David Hildenbrand <david@...hat.com>, Ryan Roberts <ryan.roberts@....com>,
 "Mike Rapoport (IBM)" <rppt@...nel.org>, Arnd Bergmann <arnd@...db.de>,
 x86@...nel.org, linux-m68k@...ts.linux-m68k.org,
 linux-fsdevel@...r.kernel.org, kasan-dev@...glegroups.com,
 linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
 Dimitri Sivanich <dimitri.sivanich@....com>,
 Alexander Viro <viro@...iv.linux.org.uk>, Muchun Song
 <muchun.song@...ux.dev>, Andrey Ryabinin <ryabinin.a.a@...il.com>,
 Miaohe Lin <linmiaohe@...wei.com>, Dennis Zhou <dennis@...nel.org>,
 Tejun Heo <tj@...nel.org>, Christoph Lameter <cl@...ux-foundation.org>,
 Uladzislau Rezki <urezki@...il.com>, Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH V2 7/7] mm: Use pgdp_get() for accessing PGD entries

On 9/19/24 02:00, kernel test robot wrote:
> Hi Anshuman,
> 
> kernel test robot noticed the following build errors:
> 
> [auto build test ERROR on char-misc/char-misc-testing]
> [also build test ERROR on char-misc/char-misc-next char-misc/char-misc-linus brauner-vfs/vfs.all dennis-percpu/for-next linus/master v6.11]
> [cannot apply to akpm-mm/mm-everything next-20240918]
> [If your patch is applied to the wrong git tree, kindly drop us a note.
> And when submitting patch, we suggest to use '--base' as documented in
> https://git-scm.com/docs/git-format-patch#_base_tree_information]
> 
> url:    https://github.com/intel-lab-lkp/linux/commits/Anshuman-Khandual/m68k-mm-Change-pmd_val/20240917-153331
> base:   char-misc/char-misc-testing
> patch link:    https://lore.kernel.org/r/20240917073117.1531207-8-anshuman.khandual%40arm.com
> patch subject: [PATCH V2 7/7] mm: Use pgdp_get() for accessing PGD entries
> config: arm-footbridge_defconfig (https://download.01.org/0day-ci/archive/20240919/202409190310.ViHBRe12-lkp@intel.com/config)
> compiler: clang version 20.0.0git (https://github.com/llvm/llvm-project 8663a75fa2f31299ab8d1d90288d9df92aadee88)
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240919/202409190310.ViHBRe12-lkp@intel.com/reproduce)
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@...el.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202409190310.ViHBRe12-lkp@intel.com/
> 
> All errors (new ones prefixed by >>):
> 
>    In file included from arch/arm/kernel/asm-offsets.c:12:
>    In file included from include/linux/mm.h:30:
>>> include/linux/pgtable.h:1245:18: error: use of undeclared identifier 'pgdp'; did you mean 'pgd'?
>     1245 |         pgd_t old_pgd = pgdp_get(pgd);
>          |                         ^
>    arch/arm/include/asm/pgtable.h:154:36: note: expanded from macro 'pgdp_get'
>      154 | #define pgdp_get(pgpd)          READ_ONCE(*pgdp)
>          |                                            ^
>    include/linux/pgtable.h:1243:48: note: 'pgd' declared here
>     1243 | static inline int pgd_none_or_clear_bad(pgd_t *pgd)
>          |                                                ^

arm (32) platform currently overrides pgdp_get() helper in the platform but
defines that like the exact same version as the generic one, albeit with a
typo which can be fixed with something like this.

diff --git a/arch/arm/include/asm/pgtable.h b/arch/arm/include/asm/pgtable.h
index be91e376df79..aedb32d49c2a 100644
--- a/arch/arm/include/asm/pgtable.h
+++ b/arch/arm/include/asm/pgtable.h
@@ -151,7 +151,7 @@ extern pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
 
 extern pgd_t swapper_pg_dir[PTRS_PER_PGD];
 
-#define pgdp_get(pgpd)         READ_ONCE(*pgdp)
+#define pgdp_get(pgdp)         READ_ONCE(*pgdp)
 
 #define pud_page(pud)          pmd_page(__pmd(pud_val(pud)))
 #define pud_write(pud)         pmd_write(__pmd(pud_val(pud)))

Regardless there is another problem here. On arm platform there are multiple
pgd_t definitions available depending on various configs but some are arrays
instead of a single data element, although platform pgdp_get() helper remains
the same for all.

arch/arm/include/asm/page-nommu.h:typedef unsigned long pgd_t[2];
arch/arm/include/asm/pgtable-2level-types.h:typedef struct { pmdval_t pgd[2]; } pgd_t;
arch/arm/include/asm/pgtable-2level-types.h:typedef pmdval_t pgd_t[2];
arch/arm/include/asm/pgtable-3level-types.h:typedef struct { pgdval_t pgd; } pgd_t;
arch/arm/include/asm/pgtable-3level-types.h:typedef pgdval_t pgd_t;

I guess it might need different pgdp_get() variants depending applicable pgd_t
definition. Will continue looking into this further but meanwhile copied Russel
King in case he might be able to give some direction.