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SubjectRe: [PATCH] USB: fix deadlock in HCD code
Date
Am Mittwoch 21 Mai 2008 15:27:50 schrieb Jiri Kosina:
> On Wed, 21 May 2008, Oliver Neukum wrote:
>
> > > hcd_urb_list_lock is used for synchronization between IRQ and non-IRQ
> > > contexts, so the non-IRQ context has to disable IRQs in order to prevent
> > > deadlocking with IRQ context.
> > Which non-irq context is that?
>
> One example -- assume usb_submit_urb() called from non-IRQ context. Then
>
> usb_hcd_submit_urb() -> rh_urb_enqueue() -> rh_queue_status() ->
> usb_hcd_link_urb_to_ep().
>

This turns out not to be the case. Interrupts are disabled.

static int rh_queue_status (struct usb_hcd *hcd, struct urb *urb)
{
int retval;
unsigned long flags;
int len = 1 + (urb->dev->maxchild / 8);

spin_lock_irqsave (&hcd_root_hub_lock, flags);
if (hcd->status_urb || urb->transfer_buffer_length < len) {
dev_dbg (hcd->self.controller, "not queuing rh status urb\n");
retval = -EINVAL;
goto done;
}

retval = usb_hcd_link_urb_to_ep(hcd, urb);

I'll investigate.

Regards
Oliver


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