On Fri, Apr 16, 2021 at 11:27:34AM -0400, Alan Stern wrote:
> On Fri, Apr 16, 2021 at 11:10:35AM +0530, Anirudh Rayabharam wrote:
> > On Tue, Apr 13, 2021 at 12:13:11PM -0400, Alan Stern wrote:
> > > Maybe we can test this reasoning by putting a delay just before the call
> > > to dum->driver->setup. That runs in the timer handler, so it's not a
> > > good place to delay, but it may be okay just for testing purposes.
> > >
> > > Hopefully this patch will make the race a lot more likely to occur. Is
> >
> > Hi Alan,
> >
> > Indeed, I was able to reproduce this bug easily on my machine with your
> > delay patch applied and using this syzkaller program:
> >
> > syz_usb_connect$cdc_ncm(0x1, 0x6e, &(0x7f0000000040)={{0x12, 0x1, 0x0, 0x2,
> > 0x0, 0x0, 0x8, 0x525, 0xa4a1, 0x40, 0x1, 0x2, 0x3, 0x1, [{{0x9, 0x2, 0x5c,
> > 0x2, 0x1, 0x0, 0x0, 0x0, {{0x9, 0x4, 0x0, 0x0, 0x1, 0x2, 0xd, 0x0, 0x0,
> > {{0x5}, {0x5}, {0xd}, {0x6}}, {{0x9, 0x5, 0x81, 0x3, 0x200}}}}}}]}},
> > &(0x7f0000000480)={0x0, 0x0, 0x0, 0x0, 0x3, [{0x0, 0x0}, {0x0, 0x0}, {0x0,
> > 0x0}]})
> >
> > I also tested doing the synchronize_irq emulation in dummy_pullup and it
> > fixed the issue. The patch is below.
>
> That's great! Thanks for testing.
>
> > Thanks!
> >
> > - Anirudh.
> >
> > diff --git a/drivers/usb/gadget/udc/dummy_hcd.c
> > b/drivers/usb/gadget/udc/dummy_hcd.c
> > index ce24d4f28f2a..931d4612d859 100644
> > --- a/drivers/usb/gadget/udc/dummy_hcd.c
> > +++ b/drivers/usb/gadget/udc/dummy_hcd.c
> > @@ -903,6 +903,12 @@ static int dummy_pullup(struct usb_gadget *_gadget,
> > int value)
> > spin_lock_irqsave(&dum->lock, flags);
> > dum->pullup = (value != 0);
> > set_link_state(dum_hcd);
> > + /* emulate synchronize_irq(): wait for callbacks to finish */
> > + while (dum->callback_usage > 0) {
> > + spin_unlock_irqrestore(&dum->lock, flags);
> > + usleep_range(1000, 2000);
> > + spin_lock_irqsave(&dum->lock, flags);
> > + }
>
> We should do this only if value == 0. No synchronization is needed when
> the pullup is turned on.
Oh right! My bad.
> Also, there should be a comment explaining that this is necessary
> because there's no other place to emulate the call made to
> synchronize_irq() in core.c:usb_gadget_remove_driver().
Will do.
> > spin_unlock_irqrestore(&dum->lock, flags);
> >
> > usb_hcd_poll_rh_status(dummy_hcd_to_hcd(dum_hcd));
> > @@ -1005,13 +1011,6 @@ static int dummy_udc_stop(struct usb_gadget *g)
> > dum->ints_enabled = 0;
> > stop_activity(dum);
> >
> > - /* emulate synchronize_irq(): wait for callbacks to finish */
> > - while (dum->callback_usage > 0) {
> > - spin_unlock_irq(&dum->lock);
> > - usleep_range(1000, 2000);
> > - spin_lock_irq(&dum->lock);
> > - }
> > -
> > dum->driver = NULL;
> > spin_unlock_irq(&dum->lock);
>
> Actually, I wanted to move this emulation code into a new subroutine and
> then call that subroutine from _both_ places. Would you like to write
Does it really need to be called from both places?
> and submit a patch that does this?
Sure! I will do that.
Thanks!
- Anirudh.
