[07/12] usb: usbtmc: Add ioctl USBTMC488_IOCTL_WAIT_SRQ

[Oliver Neukum <oneukum@suse.com>]

Am Donnerstag, den 17.05.2018, 19:03 +0200 schrieb Guido Kiener:
> +static int usbtmc488_ioctl_wait_srq(struct usbtmc_file_data *file_data,
> +                                   unsigned int __user *arg)
> +{
> +       struct usbtmc_device_data *data = file_data->data;
> +       struct device *dev = &data->intf->dev;
> +       int rv;
> +       unsigned int timeout;
> +       unsigned long expire;
> +
> +       if (!data->iin_ep_present) {
> +               dev_dbg(dev, "no interrupt endpoint present\n");
> +               return -EFAULT;
> +       }
> +
> +       if (get_user(timeout, arg))
> +               return -EFAULT;
> +
> +       expire = msecs_to_jiffies(timeout);
> +
> +       mutex_unlock(&data->io_mutex);

There is such a thing as threads sharing file descriptors.
That leads to the question what happens to the mutex if this
ioctl() is called multiple times.

	Regards
		Oliver
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