On Monday 27 August 2012 10:10:37 Sebastian Andrzej Siewior wrote: > On 08/26/2012 09:34 PM, oliver@xxxxxxxxxx wrote: > > diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c > > index c34452a..dcc10ac 100644 > > --- a/drivers/usb/dwc3/core.c > > +++ b/drivers/usb/dwc3/core.c > > @@ -99,6 +99,7 @@ void dwc3_put_device_id(int id) > > > > ret = test_bit(id, dwc3_devs); > > WARN(!ret, "dwc3: ID %d not in use\n", id); > > + smp_mb__before_clear_bit(); > > clear_bit(id, dwc3_devs); > > Why before and not after? While you own the device you may manipulate it and any memory areas the HCD accesses. So the latest time you may manipulate memory associated with the HCD is as you write out the flag set to zero. You cannot do that, therefore the barrier has to be before that. > This has more a locking semantic. Would > test_and_clear_bit() make the mb obsolete? I have no idea. The thought is evil. Regards Oliver -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
