linux-kernel - asm/mmu.h using NR_CPUS (was Re: kisskb: FAILED linux-next/axs101

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Date:   Fri, 5 May 2017 11:52:32 -0700
From:   Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:     <linux-snps-arc@...ts.infradead.org>
CC:     <noreply@...erman.id.au>, lkml <linux-kernel@...r.kernel.org>,
        <Alexey.Brodkin@...opsys.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        Michal Hocko <mhocko@...e.cz>,
        Anton Kolesov <Anton.Kolesov@...opsys.com>
Subject: asm/mmu.h using NR_CPUS (was Re: kisskb: FAILED
 linux-next/axs101_defconfig/arcompact Thu May 04, 18:53)

+CC Michal, linux-arch as it potentially affects other arches !

Hi,

On 05/04/2017 01:53 AM, noreply@...erman.id.au wrote:
> FAILED linux-next/axs101_defconfig/arcompact Thu May 04, 18:53
> 
> http://kisskb.ellerman.id.au/kisskb/buildresult/13022475/
> 
> Commit:   Add linux-next specific files for 20170504
>           ef57eb19c96fa099a578aeaed9b9d0dbcc4fe069
> Compiler: arc-buildroot-linux-uclibc-gcc (Buildroot 2015.08.1) 4.8.4
> 
> Possible errors
> ---------------
> 
> arch/arc/include/asm/mmu.h:75:21: error: 'NR_CPUS' undeclared here (not in a function)
> make[3]: *** [arch/arc/mm/ioremap.o] Error 1
> make[2]: *** [arch/arc/mm] Error 2
> make[1]: *** [arch/arc] Error 2
> arch/arc/include/asm/mmu.h:75:21: error: 'NR_CPUS' undeclared here (not in a function)
> make[3]: *** [kernel/irq/generic-chip.o] Error 1
> make[2]: *** [kernel/irq] Error 2
> make[1]: *** [kernel] Error 2
> arch/arc/include/asm/mmu.h:75:21: error: 'NR_CPUS' undeclared here (not in a function)
> make[2]: *** [mm/vmalloc.o] Error 1
> make[1]: *** [mm] Error 2
> make: *** [sub-make] Error 2

I bisected the linux-next ARC build failure (!SMP only) to a subtle side effect of
a950a30220657d ("mm, vmalloc: properly track vmalloc users") which includes
asm/pgtable.h causing the final include chain (for ARC ioremap.c) to have
asm/mmu.h (using NR_CPUS) before linux/threads.h (defining it)

The quick fix is to include linux/threads.h and this is just a heads up other
arches might run into same - although xtensa and mips with similar mm_context_t
seem to build just fine !

-Vineet