local_irq_save() disables irq completely on non-SMP which causes the hard interrupt handler unable to serve interrupts, which loses the benefit that the giveback tasklet brings in usb_hcd_giveback_urb().
One example of the issues caused by this disabling local irq is that urb->complete in uvc driver takes about 1ms, which holds the host controller to receive packets for so long that causes webcam drops data. I don't see any callers of usb_hcd_giveback_urb() holding a spin_lock, so it is safe to remove this local_irq_save/restore() around urb->complete. Signed-off-by: Bin Liu <[email protected]> --- drivers/usb/core/hcd.c | 13 ------------- 1 file changed, 13 deletions(-) diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c index 479e223..ae093f2 100644 --- a/drivers/usb/core/hcd.c +++ b/drivers/usb/core/hcd.c @@ -1751,20 +1751,7 @@ static void __usb_hcd_giveback_urb(struct urb *urb) /* pass ownership to the completion handler */ urb->status = status; - /* - * We disable local IRQs here 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. - */ - local_irq_save(flags); urb->complete(urb); - local_irq_restore(flags); - usb_anchor_resume_wakeups(anchor); atomic_dec(&urb->use_count); if (unlikely(atomic_read(&urb->reject))) -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
