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

Matthias Kaehlcke
2023-01-10T01:07:22Z

On Mon, Jan 09, 2023 at 09:19:02PM +0100, Stefan Wahren wrote:
> 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 :-)

Thanks again for testing!

I'll post a version without that loop, which shouldn't be needed as per the
rationale in my previous mail.