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

[Dave Penkler <dpenkler@gmail.com>]

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@gmail.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) {

use_count is never zero for an initialised board so this would always
return -EBUSY not allowing a board to be placed offline

> +		mutex_unlock(&board->user_mutex);
> +		return -EBUSY;
> +	}
> +
>  	if (board->autospoll_task && !IS_ERR(board->autospoll_task)) {
>  		retval = kthread_stop(board->autospoll_task);
>  		if (retval)
> @@ -262,6 +270,7 @@ int iboffline(struct gpib_board *board)
>  	board->online = 0;
>  	dev_dbg(board->gpib_dev, "board offline\n");
>  
> +	mutex_unlock(&board->user_mutex);
>  	return 0;
>  }
>  
> -- 
> 2.34.1
>