On Mon, Apr 20, 2015 at 03:02:03PM +0200, Jens Wiklander wrote: > > It appeared to me this driver was copying TPM's old architecture, > > which is very much known to be broken. > > The struct tee_device holds a shared memory pool from which shared > memory objects are allocated. These shared memory objects can be mapped > both by user space and secure world. So this is a whole other set of problems besides what was already brought up. You need to figure out a lifetime model for this shared memory that works. > To come around the problem with what should happen when the driver > is removed I'm increasing the refcount on the driver for each > allocated shared memory object and created file pointers. As long as > any resource is in use by either user space or secure world the > driver can't be unloaded. This isn't how the kernel works. The module refcount effects module unload (it protects the .text) - it does not interact with driver detatch. Userspace can trigger driver detatch (which results in tee_unregister being called) at any time via sysfs. If you properly design for that case then module unload sequencing works properly for free. Based on what I gather, I would suggest the following sequence in tee_unregister - unregister all sysfs and char dev registrations. - Write lock ops and set to null. This will error future cdev ioctls, and guarentees no driver ops callbacks are in progress, or will be started in future. - Wait until all client accesses to shared memory are released. - Command the driver to release it's side of the shared memory and wait for that to complete - Free the shared memory - deref the tee_device's struct device (match ref in tee_register) Then in your struct tee_device's release function free the tee_device memory. Replace all the module locking code with an active count in struct tee_device (see something like kernfs_drain for an example). > * Change to use the pattern (with a struct device etc) as described > above. Yes, I think Greg confirmed you need to use a struct device, and purge misc_device from the mid layer. > I can't protect the ops with just a mutex since tee_ioctl_cmd() needs to > be multithreaded. Then use a sleeping read/write lock - aka an active count. Jason -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
