linux-kernel - Re: [PATCH] hwmon: submitting-patches: Explain race conditions caused by calculations in macros

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Message-ID: <7d00f67c-298f-4fbf-9b5d-986ac4fa6d77@roeck-us.net>
Date: Thu, 4 Dec 2025 20:05:26 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: Gui-Dong Han <hanguidong02@...il.com>
Cc: linux-hwmon@...r.kernel.org, linux-kernel@...r.kernel.org,
	baijiaju1990@...il.com
Subject: Re: [PATCH] hwmon: submitting-patches: Explain race conditions
 caused by calculations in macros

On Wed, Dec 03, 2025 at 01:55:36AM +0800, Gui-Dong Han wrote:
> The current documentation advises against calculations in macros
> primarily to avoid code obfuscation. It misses the risk of concurrency
> issues.
> 
> Add a note explaining that macros evaluating arguments multiple times
> can lead to race conditions when accessing shared data.
> 
> Link: https://lore.kernel.org/all/CALbr=LYJ_ehtp53HXEVkSpYoub+XYSTU8Rg=o1xxMJ8=5z8B-g@mail.gmail.com/
> Signed-off-by: Gui-Dong Han <hanguidong02@...il.com>

Applied.

Side note: this is good enough for me. I'll be happy to accept a
separate patch with a more detailed explanation.

Thanks,
Guenter

> ---
>  Documentation/hwmon/submitting-patches.rst | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/hwmon/submitting-patches.rst b/Documentation/hwmon/submitting-patches.rst
> index 6482c4f137dc..7f7095951750 100644
> --- a/Documentation/hwmon/submitting-patches.rst
> +++ b/Documentation/hwmon/submitting-patches.rst
> @@ -82,7 +82,10 @@ increase the chances of your change being accepted.
>  * Avoid calculations in macros and macro-generated functions. While such macros
>    may save a line or so in the source, it obfuscates the code and makes code
>    review more difficult. It may also result in code which is more complicated
> -  than necessary. Use inline functions or just regular functions instead.
> +  than necessary. Such macros may also evaluate their arguments multiple times.
> +  This leads to Time-of-Check to Time-of-Use (TOCTOU) race conditions when
> +  accessing shared data without locking, for example when calculating values in
> +  sysfs show functions. Use inline functions or just regular functions instead.
>  
>  * Limit the number of kernel log messages. In general, your driver should not
>    generate an error message just because a runtime operation failed. Report