usb: gadget: f_printer: fix deadlock caused by nested spinlock

Function printer_func_disable() has called spinlock on printer_dev->lock,
and it'll call function chain of

    printer_reset_interface()
        |
	+---dwc3_gadget_ep_disable()
	        |
                +---__dwc3_gadget_ep_disable()
                        |
                        +---dwc3_remove_requests()
                                |
                                +---dwc3_gadget_giveback()
                                        |
                                        +---rx_complete()

in the protected block.

However, rx_complete() in f_printer.c calls spinlock on printer_dev->lock
again, which will cause system hang.

The following steps can reproduce this hang:

1. Build the test program from Documentation/usb/gadget_printer.txt as
   g_printer
2. Plug in the USB device to a host(such as Ubuntu).
3. on the USB device system run:
   #modprobe g_printer.ko
   #./g_printer -read_data

4. Unplug the USB device from the host

   The system will hang later.

In order to avoid this deadlock, moving the spinlock from
printer_func_disable() into printer_reset_interface() and excluding the block
of calling dwc3_gadget_ep_disable(), in which the critical resource will be
protected by its spinlock in rx_complete().

This commit will fix the system hang with the following calltrace:

INFO: rcu_preempt detected stalls on CPUs/tasks: { 3} (detected by 0, t=21006 jiffies, g=524, c=523, q=2)
sending NMI to all CPUs:
NMI backtrace for cpu 3
CPU: 3 PID: 718 Comm: irq/22-dwc3 Not tainted 3.10.38-ltsi-WR6.0.0.11_standard #2
Hardware name: Intel Corp. VALLEYVIEW B3 PLATFORM/NOTEBOOK, BIOS BYTICRB1.86C.0092.R32.1410021707 10/02/2014
task: f44f4c20 ti: f40f6000 task.ti: f40f6000
EIP: 0060:[<c1824955>] EFLAGS: 00000097 CPU: 3
EIP is at _raw_spin_lock_irqsave+0x35/0x40
EAX: 00000076 EBX: f80fad00 ECX: 00000076 EDX: 00000075
ESI: 00000096 EDI: ffffff94 EBP: f40f7e20 ESP: f40f7e18
 DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068
CR0: 8005003b CR2: b77ac000 CR3: 01c30000 CR4: 001007f0
DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000
DR6: ffff0ff0 DR7: 00000400
Stack:
 f474a720 f80fad00 f40f7e3c f80f93cc c135d486 00000000 f474a720 f468fb00
 f4bea894 f40f7e54 f7e35f19 ffffff00 f468fb00 f468fb24 00000086 f40f7e64
 f7e36577 f468fb00 f4bea810 f40f7e74 f7e365a8 f468fb00 f4bea894 f40f7e9c
Call Trace:
 [<f80f93cc>] rx_complete+0x1c/0xb0 [g_printer]
 [<c135d486>] ? vsnprintf+0x166/0x390
 [<f7e35f19>] dwc3_gadget_giveback+0xc9/0xf0 [dwc3]
 [<f7e36577>] dwc3_remove_requests+0x57/0x70 [dwc3]
 [<f7e365a8>] __dwc3_gadget_ep_disable+0x18/0x60 [dwc3]
 [<f7e366e9>] dwc3_gadget_ep_disable+0x89/0xf0 [dwc3]
 [<f80f9031>] printer_reset_interface+0x31/0x50 [g_printer]
 [<f80f9270>] printer_func_disable+0x20/0x30 [g_printer]
 [<f80e6d8b>] composite_disconnect+0x4b/0x90 [libcomposite]
 [<f7e39a8b>] dwc3_disconnect_gadget+0x38/0x43 [dwc3]
 [<f7e39ad4>] dwc3_gadget_disconnect_interrupt+0x3e/0x5a [dwc3]
 [<f7e373b8>] dwc3_thread_interrupt+0x5c8/0x610 [dwc3]
 [<c10ac518>] irq_thread_fn+0x18/0x30
 [<c10ac800>] irq_thread+0x100/0x130
 [<c10ac500>] ? irq_finalize_oneshot.part.29+0xb0/0xb0
 [<c10ac650>] ? wake_threads_waitq+0x40/0x40
 [<c10ac700>] ? irq_thread_dtor+0xb0/0xb0
 [<c1057224>] kthread+0x94/0xa0
 [<c182b337>] ret_from_kernel_thread+0x1b/0x28
 [<c1057190>] ? kthread_create_on_node+0xc0/0xc0
Signed-off-by: Fupan Li <fupan.li@windriver.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/gadget/function/f_printer.c

@@ -804,6 +804,8 @@ set_printer_interface(struct printer_dev *dev)
 
 static void printer_reset_interface(struct printer_dev *dev)
 {
+	unsigned long	flags;
+
 	if (dev->interface < 0)
 		return;
 
@@ -815,9 +817,11 @@ static void printer_reset_interface(struct printer_dev *dev)
 	if (dev->out_ep->desc)
 		usb_ep_disable(dev->out_ep);
 
+	spin_lock_irqsave(&dev->lock, flags);
 	dev->in_ep->desc = NULL;
 	dev->out_ep->desc = NULL;
 	dev->interface = -1;
+	spin_unlock_irqrestore(&dev->lock, flags);
 }
 
 /* Change our operational Interface. */
@@ -1131,13 +1135,10 @@ static int printer_func_set_alt(struct usb_function *f,
 static void printer_func_disable(struct usb_function *f)
 {
 	struct printer_dev *dev = func_to_printer(f);
-	unsigned long		flags;
 
 	DBG(dev, "%s\n", __func__);
 
-	spin_lock_irqsave(&dev->lock, flags);
 	printer_reset_interface(dev);
-	spin_unlock_irqrestore(&dev->lock, flags);
 }
 
 static inline struct f_printer_opts