On Wed, Jul 08, 2015 at 12:16:30PM +0200, Jens Wiklander wrote:
> +static void tee_device_complete_unused(struct kref *kref)
> +{
> + struct tee_device *teedev;
> +
> + teedev = container_of(kref, struct tee_device, users);
> + /* When the mutex is released, no other tee_device_get() will succeed */
> + teedev->desc = NULL;
> + complete(&teedev->c_no_users);
> +}
> +
> +void tee_device_put(struct tee_device *teedev)
> +{
> + mutex_lock(&teedev->mutex);
> + /* Shouldn't put in this state */
> + if (!WARN_ON(!teedev->desc))
> + kref_put(&teedev->users, tee_device_complete_unused);
> + mutex_unlock(&teedev->mutex);
> +}
> +
> +bool tee_device_get(struct tee_device *teedev)
> +{
> + mutex_lock(&teedev->mutex);
> + if (!teedev->desc) {
> + mutex_unlock(&teedev->mutex);
> + return false;
> + }
> + kref_get(&teedev->users);
> + mutex_unlock(&teedev->mutex);
> + return true;
> +}
If you are holding the mutex then you don't really need a kref, just a
simple active count counter.
I've been a bit learly lately about seeing krefs used for something
other than kfree, I've seen a few subtle mistakes in those schemes -
yours looks OK, only because of the lock, and the lock makes the kref
redundant..
> + cdev_init(&teedev->cdev, &tee_fops);
> + teedev->cdev.owner = teedesc->owner;
This also needs to set teedev->cdev.kobj.parent.
I'm guessing:
teedev->cdev.kobj.parent = &teedev->dev.kobj;
TPM had the same mistake..
> +void tee_device_unregister(struct tee_device *teedev)
> +{
> + if (IS_ERR_OR_NULL(teedev))
> + return;
See for some general colour on IS_ERR_OR_NULL
https://www.mail-archive.com/linux-omap@vger.kernel.org/msg78030.html
IMHO, you should never, store an ERR pointer into long term storage,
so I wonder why this is like this...
> + if (teedev->flags & TEE_DEVICE_FLAG_REGISTERED) {
> + cdev_del(&teedev->cdev);
> + device_del(&teedev->dev);
> + }
> +
> + tee_device_put(teedev);
> + wait_for_completion(&teedev->c_no_users);
Generally in a scheme like this we'd see open and release get/put the
underlying module handle to prevent driver removal while the char dev
is open. Otherwise module removal will hang here.
Jason
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