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Date:   Fri, 14 Aug 2020 10:35:52 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Xingxing Su <suxingxing@loongson.cn>
Cc:     Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] seqlock: Fix build errors
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On Fri, Aug 14, 2020 at 12:12:38PM +0800, Xingxing Su wrote:
> Fix the following build errors:
> 
> In file included from ./include/linux/time.h:6:0,
>                  from ./include/linux/compat.h:10,
>                  from arch/mips/kernel/asm-offsets.c:12:
> ./include/linux/seqlock.h: In function ‘write_seqcount_begin_nested’:
> ./include/linux/seqlock.h:286:2: error: implicit declaration of function 
>  ‘raw_smp_processor_id’ [-Werror=implicit-function-declaration]
>   lockdep_assert_preemption_disabled();
>   ^
> ./arch/mips/include/asm/smp.h: At top level:
> ./arch/mips/include/asm/smp.h:28:19: error: static declaration of 
>  ‘raw_smp_processor_id’ follows non-static declaration
>  static inline int raw_smp_processor_id(void)
>                  ^
> cc1: some warnings being treated as errors
> scripts/Makefile.build:117: recipe for target 'arch/mips/kernel/asm-offsets.s' failed
> make[1]: *** [arch/mips/kernel/asm-offsets.s] Error 1
> arch/mips/Makefile:396: recipe for target 'archprepare' failed
> make: *** [archprepare] Error 2
> 

What kernel are you building?

Commit 0cd39f4600ed ("locking/seqlock, headers: Untangle the spaghetti monster")

should have solved that I think.

> 
> Signed-off-by: Xingxing Su <suxingxing@loongson.cn>
> ---
>  v2:  update the commit message
> 
>  include/linux/seqlock.h | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
> index 54bc204..4763c13 100644
> --- a/include/linux/seqlock.h
> +++ b/include/linux/seqlock.h
> @@ -17,6 +17,7 @@
>  #include <linux/lockdep.h>
>  #include <linux/compiler.h>
>  #include <linux/kcsan-checks.h>
> +#include <linux/smp.h>
>  #include <asm/processor.h>

Wrong place, it's lockdep_assert_preemption_disabled() that requires
asm/percpu.h, and thus lockdep.h should include linux/smp. before
asm/percpu.h