linux-kernel - Re: [PATCH v5 12/36] bit_spinlock: Include missing <asm/processor.h>

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Message-ID: <61037092-ddfb-4504-9351-7f6a3e5e4616@acm.org>
Date: Fri, 19 Dec 2025 12:38:32 -0800
From: Bart Van Assche <bvanassche@....org>
To: Marco Elver <elver@...gle.com>, Peter Zijlstra <peterz@...radead.org>,
 Boqun Feng <boqun.feng@...il.com>, Ingo Molnar <mingo@...nel.org>,
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 <frederic@...nel.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
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Subject: Re: [PATCH v5 12/36] bit_spinlock: Include missing <asm/processor.h>

On 12/19/25 7:40 AM, Marco Elver wrote:
> Including <linux/bit_spinlock.h> into an empty TU will result in the
> compiler complaining:
> 
> ./include/linux/bit_spinlock.h:34:4: error: call to undeclared function 'cpu_relax'; <...>
>     34 |                         cpu_relax();
>        |                         ^
> 1 error generated.
> 
> Include <asm/processor.h> to allow including bit_spinlock.h where
> <asm/processor.h> is not otherwise included.
> 
> Signed-off-by: Marco Elver <elver@...gle.com>
> ---
>   include/linux/bit_spinlock.h | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/include/linux/bit_spinlock.h b/include/linux/bit_spinlock.h
> index c0989b5b0407..59e345f74b0e 100644
> --- a/include/linux/bit_spinlock.h
> +++ b/include/linux/bit_spinlock.h
> @@ -7,6 +7,8 @@
>   #include <linux/atomic.h>
>   #include <linux/bug.h>
>   
> +#include <asm/processor.h>  /* for cpu_relax() */
> +
>   /*
>    *  bit-based spin_lock()
>    *

The abbreviation "TU" is uncommon so it's probably a good idea to expand
it. Anyway:

Reviewed-by: Bart Van Assche <bvanassche@....org>