linux-kernel - Re: [PATCH] counter: drop chrdev

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Date:   Mon, 18 Oct 2021 08:08:21 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     David Lechner <david@...hnology.com>
Cc:     linux-iio@...r.kernel.org,
        William Breathitt Gray <vilhelm.gray@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] counter: drop chrdev_lock

On Sun, Oct 17, 2021 at 01:55:21PM -0500, David Lechner wrote:
> This removes the chrdev_lock from the counter subsystem. This was
> intended to prevent opening the chrdev more than once. However, this
> doesn't work in practice since userspace can duplicate file descriptors
> and pass file descriptors to other processes. Since this protection
> can't be relied on, it is best to just remove it.

Much better, thanks!

One remaining question:

> --- a/include/linux/counter.h
> +++ b/include/linux/counter.h
> @@ -297,7 +297,6 @@ struct counter_ops {
>   * @events:		queue of detected Counter events
>   * @events_wait:	wait queue to allow blocking reads of Counter events
>   * @events_lock:	lock to protect Counter events queue read operations
> - * @chrdev_lock:	lock to limit chrdev to a single open at a time
>   * @ops_exist_lock:	lock to prevent use during removal

Why do you still need 2 locks for the same structure?

thanks,

greg k-h