Messages in this thread | | | Date | Wed, 8 Jul 2015 11:10:26 -0600 | From | Jason Gunthorpe <> | Subject | Re: [PATCH v4 3/5] tee: generic TEE subsystem |
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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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