Am Donnerstag, den 24.05.2018, 12:59 +0000 schrieb guido@kiener-
muenchen.de:
> Zitat von Oliver Neukum <oneukum@xxxxxxxx>:
>
> > 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
>
> Multiple threads can wait with the same or different file descriptors.
> When an SRQ interrupt occurs, all threads and file descriptors are
> informed concurrently with wake_up_interruptible_all(&data->waitq);
> The "_all" is already fixed in 02/12.
No, the problem is that you will underflow io->mutex
Regards
Oliver
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