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

Stefan Wahren
2023-01-07T17:23:37Z

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+

Best regards

>
> [1] https://lore.kernel.org/r/d04bcc45-3471-4417-b30b-5cf9880d785d@i2se.com/
> [2] https://lore.kernel.org/all/Y6OrGbqaMy2iVDWB@google.com/
>
> Cc: stable@vger.kernel.org
> Fixes: 8bc063641ceb ("usb: misc: Add onboard_usb_hub driver")
> Link: https://lore.kernel.org/r/d04bcc45-3471-4417-b30b-5cf9880d785d@i2se.com/
> Link: https://lore.kernel.org/all/Y6OrGbqaMy2iVDWB@google.com/
> Reported-by: Stefan Wahren <stefan.wahren@i2se.com>
> Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
> ---
>
> drivers/usb/misc/onboard_usb_hub.c | 19 +++++++++++++------
> 1 file changed, 13 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/usb/misc/onboard_usb_hub.c b/drivers/usb/misc/onboard_usb_hub.c
> index db0844b30bbd..8bc4deb465f0 100644
> --- a/drivers/usb/misc/onboard_usb_hub.c
> +++ b/drivers/usb/misc/onboard_usb_hub.c
> @@ -27,7 +27,10 @@
>
> #include "onboard_usb_hub.h"
>
> +static void onboard_hub_attach_usb_driver(struct work_struct *work);
> +
> static struct usb_device_driver onboard_hub_usbdev_driver;
> +static DECLARE_WORK(attach_usb_driver_work, onboard_hub_attach_usb_driver);
>
> /************************** Platform driver **************************/
>
> @@ -45,7 +48,6 @@ struct onboard_hub {
> bool is_powered_on;
> bool going_away;
> struct list_head udev_list;
> - struct work_struct attach_usb_driver_work;
> struct mutex lock;
> };
>
> @@ -270,9 +272,15 @@ static int onboard_hub_probe(struct platform_device *pdev)
> *
> * This needs to be done deferred to avoid self-deadlocks on systems
> * with nested onboard hubs.
> + *
> + * If the work is already running wait for it to complete, then
> + * schedule it again to ensure that the USB devices of this onboard
> + * hub instance are bound to the USB driver.
> */
> - INIT_WORK(&hub->attach_usb_driver_work, onboard_hub_attach_usb_driver);
> - schedule_work(&hub->attach_usb_driver_work);
> + while (work_busy(&attach_usb_driver_work) & WORK_BUSY_RUNNING)
> + msleep(10);
> +
> + schedule_work(&attach_usb_driver_work);
>
> return 0;
> }
> @@ -285,9 +293,6 @@ static int onboard_hub_remove(struct platform_device *pdev)
>
> hub->going_away = true;
>
> - if (&hub->attach_usb_driver_work != current_work())
> - cancel_work_sync(&hub->attach_usb_driver_work);
> -
> mutex_lock(&hub->lock);
>
> /* unbind the USB devices to avoid dangling references to this device */
> @@ -449,6 +454,8 @@ static void __exit onboard_hub_exit(void)
> {
> usb_deregister_device_driver(&onboard_hub_usbdev_driver);
> platform_driver_unregister(&onboard_hub_driver);
> +
> + cancel_work_sync(&attach_usb_driver_work);
> }
> module_exit(onboard_hub_exit);
>