Date:   Thu, 30 Dec 2021 11:56:33 +0100
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Paulo Miguel Almeida <paulo.miguel.almeida.rodenas@gmail.com>
Cc:     realwakka@gmail.com, linux-staging@lists.linux.dev,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] staging: pi433: add comment to rx_lock mutex
 definition
Message-ID: <Yc2QYUcIAV2SY9JU@kroah.com>
References: <20211222215615.GA9361@localhost.localdomain>
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On Thu, Dec 23, 2021 at 10:56:15AM +1300, Paulo Miguel Almeida wrote:
> Checkpatch reports: CHECK: struct mutex definition without comment.
> Fix this by documenting what rx_mutex struct is used for in pi433 driver.
> 
> Signed-off-by: Paulo Miguel Almeida <paulo.miguel.almeida.rodenas@gmail.com>
> ---
> v2: ellaborate on reasons why the mutex lock is used in the driver (Req: Greg k-h)
> v1: https://lore.kernel.org/lkml/20211222093626.GA13332@localhost.localdomain/
> ---
>  drivers/staging/pi433/pi433_if.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/staging/pi433/pi433_if.c b/drivers/staging/pi433/pi433_if.c
> index 29bd37669059..1cd3d5f2df2a 100644
> --- a/drivers/staging/pi433/pi433_if.c
> +++ b/drivers/staging/pi433/pi433_if.c
> @@ -92,6 +92,17 @@ struct pi433_device {
>  	u32			rx_bytes_to_drop;
>  	u32			rx_bytes_dropped;
>  	unsigned int		rx_position;
> +	/*
> +	 * rx_lock is used to avoid race-conditions that can be triggered from userspace.
> +	 *
> +	 * For instance, if a program in userspace is reading the char device
> +	 * allocated in this module then another program won't be able to change RX
> +	 * configuration of the RF69 hardware module via ioctl and vice versa.
> +	 *
> +	 * utilization summary:
> +	 *  - pi433_read: blocks are read until rx read something (up to the buffer size)
> +	 *  - pi433_ioctl: during pending read request, change of config not allowed
> +	 */

This is nice, but way too specific, and will quickly get out-of-date.

How about something simple like:
	/* Protects all rx_* variable accesses */

thanks,

greg k-h