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You must set reslength to 0 whenever you get a ZLP > >        Regards >                Oliver > That's a good point! So that's the case, when we receive only a single ZLP, and nothing else. But we cannot return with -EAGAIN. If we do that, we're back to sqrt(1), and get stuck again. So what about modifying the service_interrupt_work to no simply set WDM_READ if resp_count is 0, but instead to check if there's any real message in the buffer, to not confuse consumers. Something like this: diff --git a/drivers/usb/class/cdc-wdm.c b/drivers/usb/class/cdc-wdm.c index 37873acd18f4..9037379f3603 100644 --- a/drivers/usb/class/cdc-wdm.c +++ b/drivers/usb/class/cdc-wdm.c @@ -1010,7 +1010,7 @@ static void service_interrupt_work(struct work_struct *work)         spin_lock_irq(&desc->iuspin);         service_outstanding_interrupt(desc); -       if (!desc->resp_count) { +       if (!desc->resp_count && (desc->length || desc->rerr)) {                 set_bit(WDM_READ, &desc->flags);                 wake_up(&desc->wait);         } Best regards, Robert