[RFC PATCH v1 2/6] USB: disable IRQs deliberately when calling complete()

[Ming Lei]

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.

Cc: Oliver Neukum <oliver at neukum.org>
Cc: Alan Stern <stern at rowland.harvard.edu>
Signed-off-by: Ming Lei <ming.lei at canonical.com>
---
 drivers/usb/core/hcd.c |   23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

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);
+	}
+
 	atomic_dec (&urb->use_count);
 	if (unlikely(atomic_read(&urb->reject)))
 		wake_up (&usb_kill_urb_queue);
-- 
1.7.9.5