On Fri, 2021-10-01 at 09:14 +0200, Greg KH wrote:
> On Thu, Sep 30, 2021 at 06:28:15PM -0700, David E. Box wrote:
> > +static int sdsi_device_open(struct inode *inode, struct file *file)
> > +{
> > + struct miscdevice *miscdev = file->private_data;
> > +
> > + get_device(miscdev->this_device);
>
> Why do you think this is needed? Shouldn't the misc core handle all of
> this for you already?
>
> > +
> > + return 0;
> > +}
> > +
> > +static int sdsi_device_release(struct inode *inode, struct file *file)
> > +{
> > +
> > + struct miscdevice *miscdev = file->private_data;
> > + struct sdsi_priv *priv = to_sdsi_priv(miscdev);
> > +
> > + if (priv->akc_owner == file)
> > + priv->akc_owner = NULL;
>
> Why is this needed?
>
> > +
> > + put_device(miscdev->this_device);
>
> I see this matches the open call, but if you do not have this in the
> open call, is it needed here as well?
>
> > + ret = devm_add_action_or_reset(priv->miscdev.this_device, sdsi_miscdev_remove, priv);
> > + if (ret)
> > + goto deregister_misc;
>
> I think this is all you need to clean up your device memory, not the
> get/put device in open/release, right?
It does clean up the memory, but it does so immediately after the device has been unregistered, even
if a file is open. The get/put ensures that if files are open, the memory isn't cleaned up until the
files are closed.
I can show that this happens without the get/put,
open()
unbind device -> devm action called -> kfree(priv)
ioctl() -> priv accessed
but it doesn't blow up. I guess because the former location of priv is accessible by container_of on
the miscdev. But that memory was freed right?
David
>
> thanks,
>
> greg k-h
