Re: Reboot/shutdown failure due to "USB: EHCI: work around silicon bug in Intel's EHCI"

[Stephen Warren <swarren-3lzwWm7+Weoh9ZMKESR00Q@public.gmane.org>]

On 03/19/2013 02:07 PM, Alan Stern wrote:
> On Tue, 19 Mar 2013, Stephen Warren wrote:
> 
>> Yes, sysrq seems to work over the serial console:-)
>>
>>>  * Will now restart
>>>
>>> *** break sent ***
>>> [  180.765213] SysRq : Show Blocked State
>>> [  180.768963]   task                PC stack   pid father
>>> [  180.774182] khubd           D c0517678     0    21      2 0x00000000
>>> [  180.780559] [<c0517678>] (__schedule+0x348/0x6dc) from [<c02ebc90>] (usb_kill_urb+0x88/0xd4)
>>> [  180.788984] [<c02ebc90>] (usb_kill_urb+0x88/0xd4) from [<c02ecb70>] (usb_start_wait_urb+0xa4/0x13c)
>>> [  180.798012] [<c02ecb70>] (usb_start_wait_urb+0xa4/0x13c) from [<c02ecd98>] (usb_control_msg+0x98/0xcc)
>>> [  180.807301] [<c02ecd98>] (usb_control_msg+0x98/0xcc) from [<c02e4394>] (hub_port_init+0x5e0/0x9d0)
>>> [  180.816242] [<c02e4394>] (hub_port_init+0x5e0/0x9d0) from [<c02e6640>] (hub_port_connect_change+0x1f4/0x970)
>>> [  180.826050] [<c02e6640>] (hub_port_connect_change+0x1f4/0x970) from [<c02e70fc>] (hub_events+0x340/0x8c4)
>>> [  180.835598] [<c02e70fc>] (hub_events+0x340/0x8c4) from [<c02e76a8>] (hub_thread+0x28/0x1b8)
>>> [  180.843941] [<c02e76a8>] (hub_thread+0x28/0x1b8) from [<c0041268>] (kthread+0xa4/0xb0)
> 
>> I assume you only want the back-traces, not the reset of the sysrq spew?
> 
> Yes.  It looks like khubd is your problem.
> 
>> BTW, I have also occasionally noticed some either hung task or RCU spew
>> related to usb_kill_urb at other times (i.e. when not rebooting), IIRC
>> (which I may not; I may be remembering what happens if I just leave the
>> reboot hung for a few minutes, as shown below):
>>
>>> [  240.670335] INFO: task khubd:21 blocked for more than 120 seconds.
>>> [  240.676516] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
>>> [  240.684336] khubd           D c0517678     0    21      2 0x00000000
> 
> Right.  It's another symptom of the same thing.  This problem occurs 
> well before shutdown -- something is causing khubd to hang and that 
> messes up everything else.
> 
> A dmesg log with CONFIG_USB_DEBUG enabled would be helpful.  We ought
> to be able to tell where khubd is getting stuck.

Hmmm. Enabling CONFIG_USB_DEBUG appears to mask the problem. I assume
this is some kind of timing/race condition, unless there's some code
with required side-effects hiding under ifdef CONFIG_USB_DEBUG somehow?
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