Re: [PATCH 1/1] usb: gadget: core: wait gadget device .release finishing at usb_del_gadget_udc

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

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?

NO!!!

> 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?

Nope.  Remove it please.

> > > > > -static void usb_udc_nop_release(struct device *dev)
> > > > > +static void usb_gadget_release(struct device *dev)
> > > > >  {
> > > > > +	struct usb_gadget *gadget;
> > > > > +
> > > > >  	dev_vdbg(dev, "%s\n", __func__);
> > > > > +
> > > > > +	gadget = container_of(dev, struct usb_gadget, dev);
> > > > > +	complete(&gadget->done);
> > > > > +	memset(dev, 0x0, sizeof(*dev));
> > > > 
> > > > No, the memory should be freed here, not memset.
> > > > 
> > >  
> > > This memory is allocated at UDC driver and is freed by UDC driver too.
> > 
> > That's wrong, the release function should be where this is released.
> 
> So, the release function should be at individual UDC driver, a common
> release function is improper, right?

Depends on how this all works, but again, the release function needs to
free the memory, otherwise this is broken.

> > And this no-op function is horrid.  There used to be documentation in
> > the kernel where I could rant about this, but instead, I'll just say,
> > "why are people trying to work around warnings we put in the core kernel
> > to fix common problems?  Do they think we did that just because we
> > wanted to be mean???"
> > 
> 
> So, like kernel doc for device_initialize said, a proper fix for dwc3
> should be zeroed gadget device memory at its own driver before the 
> gadget device register to driver core, right?

It should get a totally different, dynamically allocated structure.
NEVER recycle them.

thanks,

greg k-h