Re: [PATCH 4/7] platform/surface: aggregator_cdev: Add support for forwarding events to user-space

[Maximilian Luz]

On 6/4/21 1:32 PM, Hans de Goede wrote:
> Hi,
>
> I've one review remark inline below.
>
> On 6/4/21 1:45 AM, Maximilian Luz wrote:

[...]

> > +static int ssam_cdev_device_open(struct inode *inode, struct file *filp)
> > +{
> > +	struct miscdevice *mdev = filp->private_data;
> > +	struct ssam_cdev_client *client;
> > +	struct ssam_cdev *cdev = container_of(mdev, struct ssam_cdev, mdev);
> > +
> > +	/* Initialize client */
> > +	client = vzalloc(sizeof(*client));
> > +	if (!client)
> > +		return -ENOMEM;
> > +
> > +	client->cdev = ssam_cdev_get(cdev);
> > +
> > +	INIT_LIST_HEAD(&client->node);
> > +
> > +	mutex_init(&client->notifier_lock);
> > +
> > +	mutex_init(&client->read_lock);
> > +	mutex_init(&client->write_lock);
> > +	INIT_KFIFO(client->buffer);
> > +	init_waitqueue_head(&client->waitq);
> > +
> > +	filp->private_data = client;
> > +
> > +	/* Attach client. */
> > +	down_write(&cdev->client_lock);
> > +
> > +	if (test_bit(SSAM_CDEV_DEVICE_SHUTDOWN_BIT, &cdev->flags)) {
> > +		up_write(&cdev->client_lock);
> > +		ssam_cdev_put(client->cdev);
>
> You are missing the mutex_destroy() calls here which you are
> doing in ssam_cdev_device_release().

Thank you for noticing this! This code is based on Surface DTX code
which has the same problem, I'll send in a fix for that shortly.

> Or maybe move the mutex_init calls below this check
> (before the up_write()) since I don't think the client can
> be accessed by any code until the up_write is done?

Yes, that would also be possible, but I'd prefer adding the
mutex_destroy() calls in the failure path. To me that seems a bit easier
to reason about.

Thanks,
Max