On Tue, 18 Jun 2013, Ming Lei wrote:
> We disable local IRQs here in case of running complete() by
> tasklet to avoid possible deadlock because drivers may call
> spin_lock() to hold lock which might be acquired in one hard
> interrupt handler.
>
> The local_irq_save()/local_irq_restore() around complete()
> will be removed if current USB drivers have been cleaned up
> and no one may trigger the above deadlock situation when
> running complete() in tasklet.
This should be part of the first patch, not added on separately.
> diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
> index a272968..09a8263 100644
> --- a/drivers/usb/core/hcd.c
> +++ b/drivers/usb/core/hcd.c
> @@ -1673,7 +1673,28 @@ static void __usb_hcd_giveback_urb(struct urb *urb)
>
> /* pass ownership to the completion handler */
> urb->status = status;
> - urb->complete (urb);
> +
> + /*
> + * We disable local IRQs here in case of running complete() by
> + * tasklet to avoid possible deadlock because drivers may call
> + * spin_lock() to hold lock which might be acquired in one hard
> + * interrupt handler.
> + *
> + * The local_irq_save()/local_irq_restore() around complete()
> + * will be removed if current USB drivers have been cleaned up
> + * and no one may trigger the above deadlock situation when
> + * running complete() in tasklet.
> + */
> + if (hcd_giveback_urb_in_bh(hcd)) {
> + unsigned long flags;
> +
> + local_irq_save(flags);
> + urb->complete (urb);
> + local_irq_restore(flags);
> + } else {
> + urb->complete (urb);
> + }
> +
There's no reason to bother with the test. You might as well always do
the local_irq_save.
Alan Stern
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