Re: [PATCH 18/19] linux/include: add non-atomic version of xchg

[Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>]

On Thu, Dec 22, 2022 at 12:46:34PM +0100, Andrzej Hajda wrote:
> The pattern of setting variable with new value and returning old
> one is very common in kernel. Usually atomicity of the operation
> is not required, so xchg seems to be suboptimal and confusing in
> such cases.

FWIW,
Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>

> Signed-off-by: Andrzej Hajda <andrzej.hajda@xxxxxxxxx>
> ---
>  include/linux/non-atomic/xchg.h | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
>  create mode 100644 include/linux/non-atomic/xchg.h
> 
> diff --git a/include/linux/non-atomic/xchg.h b/include/linux/non-atomic/xchg.h
> new file mode 100644
> index 00000000000000..f7fa5dd746f37d
> --- /dev/null
> +++ b/include/linux/non-atomic/xchg.h
> @@ -0,0 +1,19 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _LINUX_NON_ATOMIC_XCHG_H
> +#define _LINUX_NON_ATOMIC_XCHG_H
> +
> +/**
> + * __xchg - set variable pointed by @ptr to @val, return old value
> + * @ptr: pointer to affected variable
> + * @val: value to be written
> + *
> + * This is non-atomic variant of xchg.
> + */
> +#define __xchg(ptr, val) ({		\
> +	__auto_type __ptr = ptr;	\
> +	__auto_type __t = *__ptr;	\
> +	*__ptr = (val);			\
> +	__t;				\
> +})
> +
> +#endif
> -- 
> 2.34.1
> 

-- 
With Best Regards,
Andy Shevchenko