This flag is a deprecated NOOP, interrupt handlers are always run
with interupts disabled.
See commit 
6932bf37 (genirq: Remove IRQF_DISABLED from core code), and
include/linux/interrupt.h:
	 * IRQF_DISABLED - keep irqs disabled when calling the action handler.
	 *                 DEPRECATED. This flag is a NOOP and scheduled to be removed
Signed-off-by: Matthijs Kooijman <matthijs@stdin.nl>
Acked-by: Paul Zimmerman <paulz@synopsys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
         * allocates the DMA buffer pool, registers the USB bus, requests the
         * IRQ line, and calls hcd_start method.
         */
-       retval = usb_add_hcd(hcd, irq, IRQF_SHARED | IRQF_DISABLED);
+       retval = usb_add_hcd(hcd, irq, IRQF_SHARED);
        if (retval < 0)
                goto error3;