lkml.org 
[lkml]   [2017]   [Nov]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH v2] usb:xhci fix panic in xhci_free_virt_devices_depth_first
From
Date


On 2017/11/6 22:00, Mathias Nyman wrote:
> On 06.11.2017 14:36, Chen Yu wrote:
>>
>>
>> On 2017/11/6 19:32, Greg KH wrote:
>>>> 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
>>>
>>> Then the bug needs to be fixed, throwing a huge kernel trace message
>>> into the kernel log is not "fixing" the problem at all, right?
>>>
>>> thanks,
>>>
>>> greg k-h
>>>
>>> .
>>>
>>
>> You are right, the way that xhci_plat_remove() to be called needs to be fixed.
>> But there is still possibility for this crash.
>> What do you think if just add an "xhci_warn" instead of "WARN_ON"?
>> + if (!vdev->real_port) {
>> + xhci_warn(xhci, "Bad vdev->real_port\n");
>> + goto out;
>> + }
>> +
>>
>
> This patch solves the issue, just drop all the error messages.
>
> vdev->real_port is not set until the the device enable/address
> stage, and we know it won't have any children yet then, so no need to
> worry about a child having tt pointers to this device.
>
> The "goto out" to xhci_free_virt_device() you do is fine here.
>
> xhci_plat_remove() is the .remove callback for the xhci platform driver.
> It might get called before a device is properly enabled/addressed.
> Not really a error. A unlikely but possible situation.
>
> xhci_free_tt_info() already has a similar check

Thanks a lot for your analysis and suggestion!
The check within xhci_free_tt_info() is a better one.
I will upload a new patch like the check in xhci_free_tt_info().

>
> Thanks
> -Mathias
>
>
> .
>

\
 
 \ /
  Last update: 2017-11-08 21:01    [W:0.057 / U:0.280 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site