linux-kernel - Re: [PATCH] Staging: gpib: iblib: iboffline check if board is in use

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Message-ID: <9632c958-9c35-4282-9e20-ce84d10a6b20@suswa.mountain>
Date: Mon, 12 May 2025 17:58:58 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Thomas Andreatta <thomasandreatta2000@...il.com>
Cc: dpenkler@...il.com, gregkh@...uxfoundation.org,
	linux-kernel@...r.kernel.org, linux-staging@...ts.linux.dev,
	Thomas Andreatta <thomas.andreatta2000@...il.com>
Subject: Re: [PATCH] Staging: gpib: iblib: iboffline check if board is in use

On Sat, May 10, 2025 at 07:24:20PM +0200, Thomas Andreatta wrote:
> Ensures that a board cannot be taken offline while it's still in use.
> 
> Signed-off-by: Thomas Andreatta <thomas.andreatta2000@...il.com>
> ---
>  drivers/staging/gpib/common/iblib.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/staging/gpib/common/iblib.c b/drivers/staging/gpib/common/iblib.c
> index 7a44517464ab..0ab5680457ac 100644
> --- a/drivers/staging/gpib/common/iblib.c
> +++ b/drivers/staging/gpib/common/iblib.c
> @@ -240,7 +240,6 @@ int ibonline(struct gpib_board *board)
>  	return 0;
>  }
>  
> -/* XXX need to make sure board is generally not in use (grab board lock?) */
>  int iboffline(struct gpib_board *board)
>  {
>  	int retval;
> @@ -250,6 +249,15 @@ int iboffline(struct gpib_board *board)
>  	if (!board->interface)
>  		return -ENODEV;
>  
> +	/* Ensure board is not in use */
> +	if (mutex_lock_interruptible(&board->user_mutex))
> +		return -ERESTARTSYS;
> +
> +	if (board->use_count > 0) {

We're not holding this mutex in ibopen() and not necessarily
in ibclose() either so this doesn't work.  It's racy.

You'd have to change the ioctl as well.

regards,
dan carpenter