Regression in net2280 locking

On Tue, 7 Aug 2018, D. Ziesche wrote:

Hello,

I use a 'USB controller: PLX Technology, Inc. Device 3380 (rev ab)' for 
a custom usb gadget.
With a more recent kernel (4.12+) the cpu hangs and the gadget device is 
not functioning at all.

I used git-bisect and a basic test gadget from the kernel tree
(tools/usb/ffs-aio-example/simple/device_app/aio_simple.c) to find the 
first
bad commit: f16443a034c7aa359ddf6f0f9bc40d01ca31faea
The bug still occurs with 4.18.0-rc7+.

Steps to reproduce:
1. Compile and run the testtool 
'tools/usb/ffs-aio-example/simple/device_app/aio_simple.c'
2. Connect with a host system
3. Disconnect from host system
4. Kernel suffers CPU lockups

Shell output:
---
$ ./a.out /dev/usb_gadget/aio_simple_gadget
Event Bind
Event Enable     <- connected to host
submit: in
submit: out
Event Suspend  <- disconnected from host
---hangs---         <- Event Disable is missing
---

Yes, I see the problem.  Commit f16443a034c7 was wrong in several 
respects.  One was fixed later in commit 7dbd8f4cabd9, but the problem 
in net2280 remained.

I think the patch below (which is mostly a reversion of the relevant
parts of f16443a034c7) should fix it.  Can you please test the patch
and let me know?

Alan Stern
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Index: usb-4.x/drivers/usb/gadget/udc/net2280.c
===================================================================

--- usb-4.x.orig/drivers/usb/gadget/udc/net2280.c
+++ usb-4.x/drivers/usb/gadget/udc/net2280.c

@@ -1545,7 +1545,7 @@ static int net2280_pullup(struct usb_gad
 		writel(tmp | BIT(USB_DETECT_ENABLE), &dev->usb->usbctl);
 	} else {
 		writel(tmp & ~BIT(USB_DETECT_ENABLE), &dev->usb->usbctl);
-		stop_activity(dev, dev->driver);
+		stop_activity(dev, NULL);
 	}
 
 	spin_unlock_irqrestore(&dev->lock, flags);

@@ -2466,8 +2466,11 @@ static void stop_activity(struct net2280
 		nuke(&dev->ep[i]);
 
 	/* report disconnect; the driver is already quiesced */
-	if (driver)
+	if (driver) {
+		spin_unlock(&dev->lock);
 		driver->disconnect(&dev->gadget);
+		spin_lock(&dev->lock);
+	}
 
 	usb_reinit(dev);
 }

@@ -3381,12 +3384,14 @@ static void handle_stat1_irqs(struct net
 			if (disconnect || reset) {
 				stop_activity(dev, dev->driver);
 				ep0_start(dev);
+				spin_unlock(&dev->lock);
 				if (reset)
 					usb_gadget_udc_reset
 						(&dev->gadget, dev->driver);
 				else
 					(dev->driver->disconnect)
 						(&dev->gadget);
+				spin_lock(&dev->lock);
 				return;
 			}
 		}