[v2] USB: cdc-wdm: don't enable interrupts in USB-giveback

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2018-06-13 19:43:55 [+0200], Oliver Neukum wrote:
> On Mi, 2018-06-13 at 18:28 +0200, Sebastian Andrzej Siewior wrote:
> > The function service_outstanding_interrupt() will unconditionally enable
> > interrupts during unlock and invoke usb_submit_urb() with GFP_KERNEL.
> > If the HCD completes in BH (like ehci does) then the context remains
> > atomic due local_bh_disable() and enabling interrupts does not change
> > this.
> 
> Hi,
Hi Oliver,

> I am just looking at your patch and I am wondering why
> wdm_in_callback() won't just call service_outstanding_interrupt()
> again and again? OK, maybe I am dense and it may well be present now,
> but it just looks to me that way.

But this part didn't change, did it? The user blocks in wdmw_read()
waiting for the WDM_READ to be set and a wakeup. After rhe wakeup it
clears the ->rerr.

| static ssize_t wdm_read
| (struct file *file, char __user *buffer, size_t count, loff_t *ppos)
| {
|…
|                        rv = wait_event_interruptible(desc->wait,
|                                 test_bit(WDM_READ, &desc->flags));
|… 
|
|                if (desc->rerr) { /* read completed, error happened */
|                         rv = usb_translate_errors(desc->rerr);
|                         desc->rerr = 0;
|                         spin_unlock_irq(&desc->iuspin);
|                         goto err;
|                 }

Maybe we should delay the WDM_READ flag in the error case until the
worker is done (before the wakeup).

> 	Regards
> 		Oliver

Sebastian
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