Re: [PATCH] usb: core: hub: hub_port_init lock controller instead of bus

[Mathias Nyman <mathias.nyman@linux.intel.com>]

On 08.02.2016 15:49, Chris Bainbridge wrote:
> The XHCI controller presents two USB buses to the system - one for USB 2
> and one for USB 3. When only one bus is locked there is a race condition
> with two threads in hub_port_init:
>
> [    8.984500] Call Trace:
> [    8.985698]  [<ffffffff81b9bab7>] schedule+0x37/0x90
> [    8.986918]  [<ffffffff817da7cd>] usb_kill_urb+0x8d/0xd0
> [    8.988130]  [<ffffffff8111e5e0>] ? wake_up_atomic_t+0x30/0x30
> [    8.989343]  [<ffffffff817dafbe>] usb_start_wait_urb+0xbe/0x150
> [    8.990561]  [<ffffffff817db10c>] usb_control_msg+0xbc/0xf0
> [    8.991766]  [<ffffffff817d07de>] hub_port_init+0x51e/0xb70
> [    8.992964]  [<ffffffff817d4697>] hub_event+0x817/0x1570
> [    8.994156]  [<ffffffff810f3e6f>] process_one_work+0x1ff/0x620
> [    8.995342]  [<ffffffff810f3dcf>] ? process_one_work+0x15f/0x620
> [    8.996528]  [<ffffffff810f4684>] worker_thread+0x64/0x4b0
> [    8.997707]  [<ffffffff810f4620>] ? rescuer_thread+0x390/0x390
> [    8.998883]  [<ffffffff810fa7f5>] kthread+0x105/0x120
> [    9.000056]  [<ffffffff810fa6f0>] ? kthread_create_on_node+0x200/0x200
> [    9.001241]  [<ffffffff81ba183f>] ret_from_fork+0x3f/0x70
> [    9.002420]  [<ffffffff810fa6f0>] ? kthread_create_on_node+0x200/0x200
>
> [    9.870837] Call Trace:
> [    9.875664]  [<ffffffff817fd36d>] xhci_setup_device+0x53d/0xa40
> [    9.876871]  [<ffffffff817fd87e>] xhci_address_device+0xe/0x10
> [    9.878068]  [<ffffffff817d047f>] hub_port_init+0x1bf/0xb70
> [    9.879262]  [<ffffffff811247ed>] ? trace_hardirqs_on+0xd/0x10
> [    9.880465]  [<ffffffff817d4697>] hub_event+0x817/0x1570
> [    9.881668]  [<ffffffff810f3e6f>] process_one_work+0x1ff/0x620
> [    9.882869]  [<ffffffff810f3dcf>] ? process_one_work+0x15f/0x620
> [    9.884074]  [<ffffffff810f4684>] worker_thread+0x64/0x4b0
> [    9.885268]  [<ffffffff810f4620>] ? rescuer_thread+0x390/0x390
> [    9.886457]  [<ffffffff810fa7f5>] kthread+0x105/0x120
> [    9.887634]  [<ffffffff810fa6f0>] ? kthread_create_on_node+0x200/0x200
> [    9.888817]  [<ffffffff81ba183f>] ret_from_fork+0x3f/0x70
> [    9.889995]  [<ffffffff810fa6f0>] ? kthread_create_on_node+0x200/0x200
>
> Which results from the two call chains:
>
> hub_port_init
>   usb_get_device_descriptor
>    usb_get_descriptor
>     usb_control_msg
>      usb_internal_control_msg
>       usb_start_wait_urb
>        usb_submit_urb / wait_for_completion_timeout / usb_kill_urb
>
> hub_port_init
>   hub_set_address
>    xhci_address_device
>     xhci_setup_device
>
> The logged kernel errors are:
>
> [    8.034843] xhci_hcd 0000:00:14.0: Timeout while waiting for setup device command
> [   13.183701] usb 3-3: device descriptor read/all, error -110
>
> On a test system this failure occurred on 6% of all boots.
>
> Hypothetically, it should perhaps be possible to set the address of the
> hub on one bus while the hub on the other bus already has an outstanding
> descriptor read request. But as this is not working reliably, fix it by
> locking the controller in hub_port_init to prevent parallel
> initialisation of both buses.
>

Most likely xhci is messed up after two device slots are in default state at the same time.
This happens when both threads are in hub_port_init() have called hub_port_reset()

The issue becomes visible when the the descriptor read and set address both fail after
the port resets.

xhci specs 4.5.3 has one tiny note about this:
"Note: Software shall not transition more than one Device Slot to the Default State at a time"

So to me, and from xhci pov this patch looks like the correct solution,
but I might be missing some usb core side details.

-Mathias