Re: [PATCH 2/2] usb: misc: onboard_hub: Move 'attach' work to the driver

Stefan Wahren
2023-01-09T20:20:18Z

Hi Matthias,

Am 09.01.23 um 18:40 schrieb Matthias Kaehlcke:
> On Sun, Jan 08, 2023 at 11:47:13AM +0100, Stefan Wahren wrote:
>> Am 07.01.23 um 18:23 schrieb Stefan Wahren:
>>> Hi Matthias,
>>>
>>> Am 06.01.23 um 00:03 schrieb Matthias Kaehlcke:
>>>> Currently each onboard_hub platform device owns an 'attach' work,
>>>> which is scheduled when the device probes. With this deadlocks
>>>> have been reported on a Raspberry Pi 3 B+ [1], which has nested
>>>> onboard hubs.
>>>>
>>>> The flow of the deadlock is something like this (with the onboard_hub
>>>> driver built as a module) [2]:
>>>>
>>>> - USB root hub is instantiated
>>>> - core hub driver calls onboard_hub_create_pdevs(), which creates the
>>>>    'raw' platform device for the 1st level hub
>>>> - 1st level hub is probed by the core hub driver
>>>> - core hub driver calls onboard_hub_create_pdevs(), which creates
>>>>    the 'raw' platform device for the 2nd level hub
>>>>
>>>> - onboard_hub platform driver is registered
>>>> - platform device for 1st level hub is probed
>>>>    - schedules 'attach' work
>>>> - platform device for 2nd level hub is probed
>>>>    - schedules 'attach' work
>>>>
>>>> - onboard_hub USB driver is registered
>>>> - device (and parent) lock of hub is held while the device is
>>>>    re-probed with the onboard_hub driver
>>>>
>>>> - 'attach' work (running in another thread) calls driver_attach(), which
>>>>     blocks on one of the hub device locks
>>>>
>>>> - onboard_hub_destroy_pdevs() is called by the core hub driver when one
>>>>    of the hubs is detached
>>>> - destroying the pdevs invokes onboard_hub_remove(), which waits for the
>>>>    'attach' work to complete
>>>>    - waits forever, since the 'attach' work can't acquire the device
>>>> lock
>>>>
>>>> Use a single work struct for the driver instead of having a work struct
>>>> per onboard hub platform driver instance. With that it isn't necessary
>>>> to cancel the work in onboard_hub_remove(), which fixes the deadlock.
>>>> The work is only cancelled when the driver is unloaded.
>>> i applied both patches for this series on top of v6.1
>>> (multi_v7_defconfig), but usb is still broken on Raspberry Pi 3 B+
> Thanks for testing.
>
>> here is the hung task output:
>>
>> [  243.682193] INFO: task kworker/1:0:18 blocked for more than 122 seconds.
>> [  243.682222]       Not tainted 6.1.0-00002-gaa61d98d165b #2
>> [  243.682233] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables
>> this message.
>> [  243.682242] task:kworker/1:0     state:D stack:0     pid:18 ppid:2
>> flags:0x00000000
>> [  243.682267] Workqueue: events onboard_hub_attach_usb_driver
>> [onboard_usb_hub]
>> [  243.682317]  __schedule from schedule+0x4c/0xe0
>> [  243.682345]  schedule from schedule_preempt_disabled+0xc/0x10
>> [  243.682367]  schedule_preempt_disabled from
>> __mutex_lock.constprop.0+0x244/0x804
>> [  243.682394]  __mutex_lock.constprop.0 from __driver_attach+0x7c/0x188
>> [  243.682421]  __driver_attach from bus_for_each_dev+0x70/0xb0
>> [  243.682449]  bus_for_each_dev from onboard_hub_attach_usb_driver+0xc/0x28
>> [onboard_usb_hub]
>> [  243.682494]  onboard_hub_attach_usb_driver [onboard_usb_hub] from
>> process_one_work+0x1ec/0x4d0
>> [  243.682534]  process_one_work from worker_thread+0x50/0x540
>> [  243.682559]  worker_thread from kthread+0xd0/0xec
>> [  243.682582]  kthread from ret_from_fork+0x14/0x2c
>> [  243.682600] Exception stack(0xf086dfb0 to 0xf086dff8)
>> [  243.682615] dfa0:                                     00000000 00000000
>> 00000000 00000000
>> [  243.682631] dfc0: 00000000 00000000 00000000 00000000 00000000 00000000
>> 00000000 00000000
>> [  243.682646] dfe0: 00000000 00000000 00000000 00000000 00000013 00000000
>> [  243.682692] INFO: task kworker/1:2:82 blocked for more than 122 seconds.
>> [  243.682703]       Not tainted 6.1.0-00002-gaa61d98d165b #2
>> [  243.682713] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables
>> this message.
>> [  243.682721] task:kworker/1:2     state:D stack:0     pid:82 ppid:2
>> flags:0x00000000
>> [  243.682741] Workqueue: events_power_efficient hub_init_func2
>> [  243.682764]  __schedule from schedule+0x4c/0xe0
>> [  243.682785]  schedule from schedule_preempt_disabled+0xc/0x10
>> [  243.682808]  schedule_preempt_disabled from
>> __mutex_lock.constprop.0+0x244/0x804
>> [  243.682833]  __mutex_lock.constprop.0 from hub_activate+0x584/0x8b0
>> [  243.682859]  hub_activate from process_one_work+0x1ec/0x4d0
>> [  243.682883]  process_one_work from worker_thread+0x50/0x540
>> [  243.682907]  worker_thread from kthread+0xd0/0xec
>> [  243.682927]  kthread from ret_from_fork+0x14/0x2c
>> [  243.682944] Exception stack(0xf1509fb0 to 0xf1509ff8)
>> [  243.682958] 9fa0:                                     00000000 00000000
>> 00000000 00000000
>> [  243.682974] 9fc0: 00000000 00000000 00000000 00000000 00000000 00000000
>> 00000000 00000000
>> [  243.682988] 9fe0: 00000000 00000000 00000000 00000000 00000013 00000000
>> [  243.683023] INFO: task kworker/1:4:257 blocked for more than 122 seconds.
>> [  243.683034]       Not tainted 6.1.0-00002-gaa61d98d165b #2
>> [  243.683043] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables
>> this message.
>> [  243.683051] task:kworker/1:4     state:D stack:0     pid:257 ppid:2
>> flags:0x00000000
>> [  243.683071] Workqueue: events_power_efficient hub_init_func2
>> [  243.683092]  __schedule from schedule+0x4c/0xe0
>> [  243.683113]  schedule from schedule_preempt_disabled+0xc/0x10
>> [  243.683135]  schedule_preempt_disabled from
>> __mutex_lock.constprop.0+0x244/0x804
>> [  243.683160]  __mutex_lock.constprop.0 from hub_activate+0x584/0x8b0
>> [  243.683184]  hub_activate from process_one_work+0x1ec/0x4d0
>> [  243.683209]  process_one_work from worker_thread+0x50/0x540
>> [  243.683233]  worker_thread from kthread+0xd0/0xec
>> [  243.683253]  kthread from ret_from_fork+0x14/0x2c
>> [  243.683270] Exception stack(0xf09d9fb0 to 0xf09d9ff8)
>> [  243.683283] 9fa0:                                     00000000 00000000
>> 00000000 00000000
>> [  243.683299] 9fc0: 00000000 00000000 00000000 00000000 00000000 00000000
>> 00000000 00000000
>> [  243.683313] 9fe0: 00000000 00000000 00000000 00000000 00000013 00000000
> Does commenting the following help:
>
> while (work_busy(&attach_usb_driver_work) & WORK_BUSY_RUNNING)
> msleep(10);
>
> ?
Yes, it does. I restarted the board multiple times and it never hang :-)