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    SubjectRe: [PATCH 5/5] platform/x86: Add Intel Software Defined Silicon driver
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    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


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