>
> On 20-07-31 10:12:48, Alan Stern wrote:
> > On Fri, Jul 31, 2020 at 02:06:20PM +0000, Peter Chen wrote:
> > > On 20-07-31 14:25:20, Greg Kroah-Hartman wrote:
> > > > On Fri, Jul 31, 2020 at 12:11:32PM +0000, Peter Chen wrote:
> > > >
> > > > Grab a reference from somewhere else and do not give it up for a
> > > > long time.
> > > >
> > >
> > > So wait_for_completion_timeout is suitable? The similar use case is
> > > when we open the file at the USB Drive at Windows, and we click
> > > "Eject", it will say "The device is currently in use", and refuse our "Eject"
> > > operation.
> > >
> > > When we try to remove the gadget, if the gadget is in use, we could
> > > refuse the remove operation, reasonable?
> >
> > No, the real solution is to fix the UDC drivers. They need to
> > allocate the gadget structure dynamically instead of reusing it. And
> > they should have a real release routine that deallocates the gadget structure.
> >
> > Alan Stern
>
> So, the basic routine should like below. I thought the usb_gadget should be
> deallocated before the UDC driver remove itself (UDC device is the parent of
> usb_gadget device), I may not need to wrong about it, it is just a memory region, it
> could release later.
>
> xxx_udc_release(struct device *gadget_dev) {
> struct usb_gadget *gadget = container_of(gadget_dev, struct
> usb_gadget, dev);
> kfree(gadget);
> }
>
>
> xxx_udc_probe(pdev)
> {
> udc_priv_data = kzalloc(sizeof(*udc_priv_data), GFP_KERNEL);
> gadget = kzalloc(sizeof(struct usb_gadget), GFP_KERNEL);
> udc_priv_data->gadget = gadget;
> ...
> usb_add_gadget_udc_release(&pdev->dev, gadget, xxx_udc_release);
>
> }
>
> At xxx_udc_remove(pdev)
> {
> usb_del_gadget_udc(udc_priv_data->gadget);
> /* need to never reference udc_priv_data->gadget any more */
> udc_priv_data other deinit;
> kfree(udc_priv_data);
> }
>
> Since all structures xxx_udc_release uses are common one, it could replace
> usb_udc_nop_release at udc/core.c.
>
Since gadget structure is allocated at UDC drivers, I think it should be freed at
the same place. Current common release function at udc/core.c may not a
good idea per our discussion.
Peter
