On Sun, Jun 20, 2021 at 11:53:18AM +0800, linyyuan@xxxxxxxxxxxxxx wrote:
> On 2021-06-20 11:46, linyyuan@xxxxxxxxxxxxxx wrote:
> > On 2021-06-20 10:13, Alan Stern wrote:
> > > On Sat, Jun 19, 2021 at 11:43:08PM +0800, Linyu Yuan wrote:
> > > > currently most gadget driver have a pointer to save
> > > > struct usb_gadget_driver from upper layer,
> > > > it allow upper layer set and unset of the pointer.
> > > >
> > > > there is race that upper layer unset the pointer first,
> > > > but gadget driver use the pointer later,
> > > > and it cause system crash due to NULL pointer access.
> > >
> > > This race has already been fixed in Greg's usb-next branch. See
> > > commit
> > > 7dc0c55e9f30 ("USB: UDC core: Add udc_async_callbacks gadget op") and
> > > following commits 04145a03db9d ("USB: UDC: Implement
> > > udc_async_callbacks in dummy-hcd") and b42e8090ba93 ("USB: UDC:
> > > Implement udc_async_callbacks in net2280").
> > >
> > thanks, this is better, lower driver only need change several places.
> > > You just need to write a corresponding patch implementing the
> > > async_callbacks op for dwc3.
> > yes, i will do.
> > >
> Alan, i want to discuss your suggestion again in b42e8090ba93 ("USB: UDC:
> Implement udc_async_callbacks in net2280")
>
> + if (dev->async_callbacks) { ----> if CPU1 saw this
> is true
> + spin_unlock(&dev->lock); ---> CPU2 get lock
> after this unlock,
> it will set async_callbacks to false, then follow call also crash, right ?
> + tmp = dev->driver->setup(&dev->gadget,
> &u.r);
> + spin_lock(&dev->lock);
> + }
No, this is okay. The reason is because usb_gadget_remove_driver (CPU2
in your example) does this:
usb_gadget_disable_async_callbacks(udc);
if (udc->gadget->irq)
synchronize_irq(udc->gadget->irq);
udc->driver->unbind(udc->gadget);
usb_gadget_udc_stop(udc);
The synchronize_irq call will make CPU2 wait until CPU1 has finished
handling the interrupt for the setup packet. The system won't crash,
because dev->driver->setup will be called before unbind and udc_stop
instead of after.
Alan Stern
