USB: ci13xxx_udc: fix deadlock during rmmod

The inline documentation of _gadget_stop_activity() states that the
function should be called holding the udc->lock. This however will
result in a deadlock, because _gadget_stop_activity() takes the udc->lock.

During normal operation _gadget_stop_activity() is always called unlocked,
but in ci13xxx_stop() it's called locked, this results in the following
deadlock during rmmod of a gadget driver.

This patch fixes the deadlock by calling _gadget_stop_activity() always
unlocked, the inline documentation is adjusted accordingly.

=============================================
[ INFO: possible recursive locking detected ]
3.1.0-rc6+ #159
---------------------------------------------
rmmod/121 is trying to acquire lock:
 (udc_lock){-.-...}, at: [<c0229048>] _gadget_stop_activity+0x18/0x154

but task is already holding lock:
 (udc_lock){-.-...}, at: [<c02291e0>] ci13xxx_stop+0x5c/0x164

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(udc_lock);
  lock(udc_lock);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

2 locks held by rmmod/121:
 #0:  (udc_lock#2){+.+.+.}, at: [<c02286c0>] usb_gadget_unregister_driver+0x34/0x88
 #1:  (udc_lock){-.-...}, at: [<c02291e0>] ci13xxx_stop+0x5c/0x164

stack backtrace:
[<c000d41c>] (unwind_backtrace+0x0/0xf0) from [<c0056f94>] (check_deadlock.clone.24+0x284/0x2c4)
[<c0056f94>] (check_deadlock.clone.24+0x284/0x2c4) from [<c00589ac>] (validate_chain.clone.25+0x430/0x6fc)
[<c00589ac>] (validate_chain.clone.25+0x430/0x6fc) from [<c0059bac>] (__lock_acquire+0x494/0x8f0)
[<c0059bac>] (__lock_acquire+0x494/0x8f0) from [<c005a698>] (lock_acquire+0x98/0x1a8)
[<c005a698>] (lock_acquire+0x98/0x1a8) from [<c02f12a4>] (_raw_spin_lock_irqsave+0x64/0xa0)
[<c02f12a4>] (_raw_spin_lock_irqsave+0x64/0xa0) from [<c0229048>] (_gadget_stop_activity+0x18/0x154)
[<c0229048>] (_gadget_stop_activity+0x18/0x154) from [<c0229234>] (ci13xxx_stop+0xb0/0x164)
[<c0229234>] (ci13xxx_stop+0xb0/0x164) from [<c022867c>] (usb_gadget_remove_driver+0x88/0x98)
[<c022867c>] (usb_gadget_remove_driver+0x88/0x98) from [<c02286f4>] (usb_gadget_unregister_driver+0x68/0x88)
[<c02286f4>] (usb_gadget_unregister_driver+0x68/0x88) from [<c0065f2c>] (sys_delete_module+0x1fc/0x26c)
[<c0065f2c>] (sys_delete_module+0x1fc/0x26c) from [<c00092a0>] (ret_fast_syscall+0x0/0x38)
BUG: spinlock lockup on CPU#0, rmmod/121, c05b1644
[<c000d41c>] (unwind_backtrace+0x0/0xf0) from [<c01da000>] (do_raw_spin_lock+0x128/0x144)
[<c01da000>] (do_raw_spin_lock+0x128/0x144) from [<c02f12c8>] (_raw_spin_lock_irqsave+0x88/0xa0)
[<c02f12c8>] (_raw_spin_lock_irqsave+0x88/0xa0) from [<c0229048>] (_gadget_stop_activity+0x18/0x154)
[<c0229048>] (_gadget_stop_activity+0x18/0x154) from [<c0229234>] (ci13xxx_stop+0xb0/0x164)
[<c0229234>] (ci13xxx_stop+0xb0/0x164) from [<c022867c>] (usb_gadget_remove_driver+0x88/0x98)
[<c022867c>] (usb_gadget_remove_driver+0x88/0x98) from [<c02286f4>] (usb_gadget_unregister_driver+0x68/0x88)
[<c02286f4>] (usb_gadget_unregister_driver+0x68/0x88) from [<c0065f2c>] (sys_delete_module+0x1fc/0x26c)
[<c0065f2c>] (sys_delete_module+0x1fc/0x26c) from [<c00092a0>] (ret_fast_syscall+0x0/0x38)

Tested-by: Pavankumar Kondeti <pkondeti@codeaurora.org>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/gadget/ci13xxx_udc.c

@@ -1613,7 +1613,6 @@ __acquires(mEp->lock)
  * @gadget: gadget
  *
  * This function returns an error code
- * Caller must hold lock
  */
 static int _gadget_stop_activity(struct usb_gadget *gadget)
 {
@@ -2707,7 +2706,9 @@ static int ci13xxx_stop(struct usb_gadget_driver *driver)
 		if (udc->udc_driver->notify_event)
 			udc->udc_driver->notify_event(udc,
 			CI13XXX_CONTROLLER_STOPPED_EVENT);
+		spin_unlock_irqrestore(udc->lock, flags);
 		_gadget_stop_activity(&udc->gadget);
+		spin_lock_irqsave(udc->lock, flags);
 		pm_runtime_put(&udc->gadget.dev);
 	}