USB: pxa27x_udc: Fix deadlocks on request queueing

As reported by Antonio, there are cases where the ep->lock
can be taken twice, triggering a deadlock.
The typical sequence is :
 irq_handler
   \
    -> gadget.complete()
       \
        -> pxa27x_udc.pxa_ep_queue() : ep->lock is taken
           \
            -> gadget.complete()
               \
                -> pxa27x_udc.pxa_ep_queue() : ep->lock is taken
                                               ==> *deadlock*
The patch fixes this by :
 - releasing the lock each time gadget.complete() is called
 - adding a check in handle_ep() to detect a recursive call,
   in which case the function becomes on no-op.

The patch is still not good enough for ep0. For this unique
endpoint, another well thought over patch will be needed.

Reported-by: Antonio Ospite <ospite@studenti.unina.it>
Tested-by: Antonio Ospite <ospite@studenti.unina.it>
Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Cc: David Brownell <dbrownell@users.sourceforge.net>
Cc: Eric Miao <eric.y.miao@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 6 insertions, 0 deletions

diff --git a/drivers/usb/gadget/pxa27x_udc.h b/drivers/usb/gadget/pxa27x_udc.h
index e25225e2658..ff61e4866e8 100644
--- a/drivers/usb/gadget/pxa27x_udc.h
+++ b/drivers/usb/gadget/pxa27x_udc.h
@@ -318,6 +318,11 @@ struct udc_usb_ep {
  * @queue: requests queue
  * @lock: lock to pxa_ep data (queues and stats)
  * @enabled: true when endpoint enabled (not stopped by gadget layer)
+ * @in_handle_ep: number of recursions of handle_ep() function
+ * 	Prevents deadlocks or infinite recursions of types :
+ *	  irq->handle_ep()->req_done()->req.complete()->pxa_ep_queue()->handle_ep()
+ *      or
+ *        pxa_ep_queue()->handle_ep()->req_done()->req.complete()->pxa_ep_queue()
  * @idx: endpoint index (1 => epA, 2 => epB, ..., 24 => epX)
  * @name: endpoint name (for trace/debug purpose)
  * @dir_in: 1 if IN endpoint, 0 if OUT endpoint
@@ -346,6 +351,7 @@ struct pxa_ep {
 	spinlock_t		lock;		/* Protects this structure */
 						/* (queues, stats) */
 	unsigned		enabled:1;
+	unsigned		in_handle_ep:1;
 
 	unsigned		idx:5;
 	char			*name;