Re: [PATCH v2 6/6] Revert "usb: udc: allow adding and removing the same gadget device"

[Peter Chen <peter.chen@nxp.com>]

On 20-08-19 10:52:36, stern@rowland.harvard.edu wrote:
> On Wed, Aug 19, 2020 at 01:31:14AM +0000, Peter Chen wrote:
> > On 20-08-18 10:46:55, stern@rowland.harvard.edu wrote:
> > > On Tue, Aug 18, 2020 at 10:05:51AM +0000, Peter Chen wrote:
> > > >  
> > > > > >
> > > > > > diff --git a/drivers/usb/gadget/udc/core.c
> > > > > > b/drivers/usb/gadget/udc/core.c index 473e74088b1f..43351b0af569
> > > > > > 100644
> > > > > > --- a/drivers/usb/gadget/udc/core.c
> > > > > > +++ b/drivers/usb/gadget/udc/core.c
> > > > > > @@ -1386,7 +1386,6 @@ void usb_del_gadget_udc(struct usb_gadget
> > > > > > *gadget)  {
> > > > > >  	usb_del_gadget(gadget);
> > > > > >  	usb_put_gadget(gadget);
> > > > > > -	memset(&gadget->dev, 0x00, sizeof(gadget->dev));
> > > > > 
> > > > > Shouldn't you do this patch earlier in the series, as the
> > > > > usb_put_gadget() call could have freed the memory that is being cleared here?
> > > > > 
> > > > 
> > > > If I did it earlier, it would cause dwc3 break if people do 'git bisect', dwc3 issue is
> > > > fixed at patch 5.
> > > 
> > > If you use the patch I posted earlier:
> > > 
> > > 	https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fmarc.info%2F%3Fl%3Dlinux-usb%26m%3D159605415210351%26w%3D2&data=02%7C01%7Cpeter.chen%40nxp.com%7Cac0a92404ea34c230dd208d8444f83d3%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C637334455595715503&sdata=whweZozRiWD%2B4iRFz7zvEahWAqQYkQQ8tHlRSiU%2Fj7I%3D&reserved=0
> > > 
> > > instead of this one then dwc3 would continue to work correctly during 
> > > the intermediate stages of the series.
> > > 
> > 
> > But at last, we don't want below at .release function
> > 
> > 	memset(dev, 0, sizeof(*dev));
> > 
> > It still needs another patch to delete it after dwc3 changes,
> > and it changes .release function name to usb_udc_zero_release,
> > this change may also not be needed.
> > 
> > Or I only do move memory clear operation at the first patch, and
> > delete it at the last patch, it could let the reader not see
> > the memory clear operation at the usb_del_gadget during the patch
> > series.
> 
> One way or another, the existing code is wrong.  I guess the best we can 
> do for now is to let it remain wrong during the patch series, rather 
> than changing it to be wrong in a different way.
> 
> To put it another way, we already run the risk of clearing memory that 
> has been freed.  The series does not make that risk any worse, and it 
> eventually fixes the problem.
> 
> This means your patch should remain in its position at the end of the 
> series.
> 

Thank.

If you think my sequence during the patch series is OK, would you
please add your reviewed-by below?

https://www.spinics.net/lists/linux-usb/msg199291.html

-- 

Thanks,
Peter Chen