Re: [PATCH v2] usb:xhci fix panic in xhci_free_virt_devices_depth_first

[Chen Yu]

Hi,

On 2017/11/6 16:31, Greg KH wrote:
> On Mon, Nov 06, 2017 at 04:20:23PM +0800, Yu Chen wrote:
>> From: Yu Chen <chenyu56@xxxxxxxxxx>
>>
>> Check vdev->real_port 0 to avoid panic
>> [    9.261347] [<ffffff800884a390>] xhci_free_virt_devices_depth_first+0x58/0x108
>> [    9.261352] [<ffffff800884a814>] xhci_mem_cleanup+0x1bc/0x570
>> [    9.261355] [<ffffff8008842de8>] xhci_stop+0x140/0x1c8
>> [    9.261365] [<ffffff80087ed304>] usb_remove_hcd+0xfc/0x1d0
>> [    9.261369] [<ffffff80088551c4>] xhci_plat_remove+0x6c/0xa8
>> [    9.261377] [<ffffff80086e928c>] platform_drv_remove+0x2c/0x70
>> [    9.261384] [<ffffff80086e6ea0>] __device_release_driver+0x80/0x108
>> [    9.261387] [<ffffff80086e7a1c>] device_release_driver+0x2c/0x40
>> [    9.261392] [<ffffff80086e5f28>] bus_remove_device+0xe0/0x120
>> [    9.261396] [<ffffff80086e2e34>] device_del+0x114/0x210
>> [    9.261399] [<ffffff80086e9e00>] platform_device_del+0x30/0xa0
>> [    9.261403] [<ffffff8008810bdc>] dwc3_otg_work+0x204/0x488
>> [    9.261407] [<ffffff80088133fc>] event_work+0x304/0x5b8
>> [    9.261414] [<ffffff80080e31b0>] process_one_work+0x148/0x490
>> [    9.261417] [<ffffff80080e3548>] worker_thread+0x50/0x4a0
>> [    9.261421] [<ffffff80080e9ea0>] kthread+0xe8/0x100
>> [    9.261427] [<ffffff8008083680>] ret_from_fork+0x10/0x50
>>
>> The problem can occur if xhci_plat_remove() is called shortly after
>> xhci_plat_probe(). While xhci_free_virt_devices_depth_first been
>> called before the device has been setup and get real_port initialized.
>> The problem occurred on Hikey960 and was reproduced by Guenter Roeck
>> on Kevin with chromeos-4.4.
>>
>> Cc: Guenter Roeck <groeck@xxxxxxxxxx>
>> Signed-off-by: Fan Ning <fanning4@xxxxxxxxxxxxx>
>> Signed-off-by: Li Rui <lirui39@xxxxxxxxxxxxx>
>> Signed-off-by: yangdi <yangdi10@xxxxxxxxxxxxx>
>> Signed-off-by: Yu Chen <chenyu56@xxxxxxxxxx>
>>
>> ---
>>  drivers/usb/host/xhci-mem.c | 4 ++++
>>  1 file changed, 4 insertions(+)
>>
>> diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
>> index 2a82c927ded2..0361b4a58f59 100644
>> --- a/drivers/usb/host/xhci-mem.c
>> +++ b/drivers/usb/host/xhci-mem.c
>> @@ -947,6 +947,9 @@ void xhci_free_virt_devices_depth_first(struct xhci_hcd *xhci, int slot_id)
>>  	if (!vdev)
>>  		return;
>>  
>> +	if (WARN_ON(!vdev->real_port))
> 
> Ok, now you are sending a lot of mess to the kernel log, so what can a
> user do about it?
> 
> How can this ever happen?  Is it a hardware error, or a kernel driver
> logic error?
> 
> thanks,
> 
> greg k-h
> 
> .
> 

The problem is a driver logic error, it can reproduced if xhci_plat_remove() is
called shortly after xhci_plat_probe() while xhci_alloc_virt_device has been called
but real_port has not been initialized in xhci_setup_addressable_virt_dev.
A simple process is as below:
	xhci_plat_probe()
               |
	usb_add_hcd()					xhci_plat_remove()
	       |						|
	find some device				usb_remove_hcd()
	       |						|
	hub_port_connect() -> usb_alloc_dev()		usb_disconnect()
	       |						|
	before hub_enable_device()			xhci_stop()
								|
							xhci_mem_cleanup()
								|
							xhci_free_virt_devices_depth_first()
								|
							real_port is 0 access xhci->rh_bw[vdev->real_port-1]

The problem came from https://bugs.96boards.org/show_bug.cgi?id=535
Also look at crbug.com/700041