Re: [linux-next:master] BUILD REGRESSION 0a6f624a86e766a27d23cbb73c23be62231d10ff

From: Andrew Morton <akpm@linux-foundation.org>
To: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: kernel test robot <lkp@intel.com>,
	Linux Memory Management List <linux-mm@kvack.org>,
	linux-arm-kernel@lists.arm.linux.org.uk,
	Russell King <rmk@arm.linux.org.uk>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Linus Walleij <linus.walleij@linaro.org>,
	Ard Biesheuvel <ardb@kernel.org>
Subject: Re: [linux-next:master] BUILD REGRESSION 0a6f624a86e766a27d23cbb73c23be62231d10ff
Date: Sun, 8 Nov 2020 18:55:22 -0800	[thread overview]
Message-ID: <20201108185522.a581d330cd4a9b25f5cbd339@linux-foundation.org> (raw)
In-Reply-To: <30c06c32-e3dd-4ce9-606b-d5731c0ae27c@arm.com>

On Mon, 9 Nov 2020 08:20:05 +0530 Anshuman Khandual <anshuman.khandual@arm.com> wrote:

> 
> 
> On 11/7/20 10:37 AM, Andrew Morton wrote:
> > On Fri, 06 Nov 2020 08:19:36 +0800 kernel test robot <lkp@intel.com> wrote:
> > 
> >> tree/branch: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git  master
> >> branch HEAD: 0a6f624a86e766a27d23cbb73c23be62231d10ff  Add linux-next specific files for 20201105
> >>
> >> Error/Warning reports:
> >>
> >> https://lore.kernel.org/linux-mm/202010281624.9m2gZw45-lkp@intel.com
> >> https://lore.kernel.org/linux-mm/202010290238.M1tDrV8p-lkp@intel.com
> >> https://lore.kernel.org/linux-mm/202010291054.WEZO3olr-lkp@intel.com
> >> https://lore.kernel.org/linux-mm/202011020749.5XQ3Hfzc-lkp@intel.com
> >>
> >> ...
> >>
> >> mm/kasan/init.c:318:9: warning: variable 'pud' set but not used [-Wunused-but-set-variable]
> >>
> > 
> > This is because mm/kasan/init.c does
> > 
> > static void kasan_free_pud(pud_t *pud_start, p4d_t *p4d)
> > {
> > 	pud_t *pud;
> > 	int i;
> > 
> > 	for (i = 0; i < PTRS_PER_PUD; i++) {
> > 		pud = pud_start + i;
> > 		if (!pud_none(*pud))
> > 			return;
> > 	}
> > 
> > 	pud_free(&init_mm, (pud_t *)page_to_virt(p4d_page(*p4d)));
> > 	p4d_clear(p4d);
> > }
> > 
> > but arch/arm/include/asm/pgtable-2level.h does
> > 
> > #define pud_none(pud)           (0)
> > 
> > The solution here is for the arm implementation to reference `pud'. 
> > Typically this is done via the use of an empty static inline C function
> > rather than a macro.  But really all of these
> > 
> > #define pud_none(pud)           (0)
> > #define pud_bad(pud)            (0)
> > #define pud_present(pud)        (1)
> > #define pud_clear(pudp)         do { } while (0)
> > #define set_pud(pud,pudp)       do { } while (0)
> > 
> > should be thus converted.
> > 
> > Could someone in arm world please attend to this?
> 
> + Ard Biesheuvel <ardb@kernel.org>
> + Linus Walleij <linus.walleij@linaro.org>
> 
> There were some earlier discussions to solve this in a different way.
> 
> https://lore.kernel.org/linux-mm/CACRpkdbAXCMTW--BmVs8SQ_u5baaeUob+U57E=4=CrMxWtMO2g@mail.gmail.com/
> 
> with a subsequent follow up patch.
> 
> https://lore.kernel.org/linux-arm-kernel/20201106085157.11211-1-linus.walleij@linaro.org/

Yes, but why?  macros-pretending-to-be-functions just keep on causing
problems and they're so unnecessary.  Why not just write functions in
the first place??   Did anyone try implementing that?