Re: [PATCH] usb: gadget: f_printer: fix the bug of deadlock caused by nested spinlock

[fupan <fupan.li@windriver.com>]

On 08/03/2015 10:47 PM, Felipe Balbi wrote:
> Hi,
>
> On Mon, Aug 03, 2015 at 07:19:43PM +0800, fupan.li@windriver.com wrote:
>> From: fli <fupan.li@windriver.com>
>>
>> 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>
> Thanks, out of curiosity, do you plan on sending a glue layer for
> Windriver's DWC3 ?
No, just this fix patch.

Fupan
>
> cheers
>