On Wed, Aug 10, 2016 at 09:49:22PM -0700, Dan Williams wrote: > Where dax_dev_release() is the f_op->release() method, and is > implemented to simply drop the final references on our driver objects: > > struct dax_dev *dax_dev = filp->private_data; > struct device *dev = dax_dev->dev; > > dev_dbg(dax_dev->dev, "%s\n", __func__); > put_device(dev); > dax_dev_put(dax_dev); > > The dax_dev object embeds a 'struct cdev' which means f_op->release() > may free cdev, so __fput() needs to drop the cdev reference before > calling f_op->release().
NAK. You *can't* free a structure that contains kobj with currently positive refcount. Ever. If you embed a struct kobj into something, you must use the refcount of that kobj (or one of its ancestors) to control the lifetime of containing object. If your dax_dev_put() can trigger freeing of dax_dev despite the still-positive refcount of embedded cdev.kobj, it is fundamentally broken.
