Hi Tzung-Bi, On Tue, Sep 02, 2025 at 09:18:47PM +0800, Tzung-Bi Shih wrote: > On Fri, Aug 29, 2025 at 08:50:01PM +0800, Tzung-Bi Shih wrote: > > On Fri, Aug 29, 2025 at 11:28:55AM +0000, Dmitry Torokhov wrote: > > > On Thu, Aug 28, 2025 at 08:35:56AM +0000, Tzung-Bi Shih wrote: > > > > A race is observed when cros_ec_lpc and cros-ec-keyb are all built as > > > > modules. cros_ec_lpc is cros-ec-keyb's parent. However, they can be > > > > probed at the same time. > > > > > > > > Example: > > > > > > > > + -----------------------------------------------------------------+ > > > > | Some init process (e.g. udevd) | deferred_probe_work_func worker | > > > > + -----------------------------------------------------------------+ > > > > | Probe cros-ec-keyb. | | > > > > | - Decide to defer[1]. | | > > > > | | A device bound to a driver[2]. | > > > > | Probe cros_ec_lpc. | | > > > > | - Init the struct[3]. | | > > > > | | Retry cros-ec-keyb from the | > > > > | | deferred list[4]. | > > > > | | - Won't defer again as [3]. | > > > > | | - Access uninitialized data in | > > > > | | the struct. | > > > > | - Register the device. | | > > > > + -----------------------------------------------------------------+ > > > > > > > > [1] https://elixir.bootlin.com/linux/v6.16/source/drivers/input/keyboard/cros_ec_keyb.c#L707 > > > > [2] https://elixir.bootlin.com/linux/v6.16/source/drivers/base/dd.c#L405 > > > > [3] https://elixir.bootlin.com/linux/v6.16/source/drivers/platform/chrome/cros_ec_lpc.c#L644 > > > > [4] https://elixir.bootlin.com/linux/v6.16/source/drivers/base/dd.c#L418 > > > > > > > > Note that the device link[5] can't help as in the observed environment, > > > > the devices are already added via device_add()[6]. > > > > > > > > [5] https://www.kernel.org/doc/html/latest/driver-api/device_link.html#usage > > > > [6] https://elixir.bootlin.com/linux/v6.16/source/drivers/acpi/acpi_platform.c#L177 > > > > > > > > The series fixes the issue by ensuring the struct is ready for accessing > > > > before continuing to probe cros-ec-keyb. > > > > > > Why is the keyboard platform device instantiated before the transport > > > (cros_ec_lpc) is done initializing? I think this is the root of the > > > issue... > > > > I may misunderstand but it seems to me: > > > > - The ACPI bus enumerated and instantiated the platform devices[6] first. > > > > - The keyboard platform device was probed when `cros_ec_keyb_driver` > > registered. It deferred as its parent's drvdata was NULL[1]. > > > > - The transport platform device was probed when `cros_ec_lpc_driver` > > registered. It set the drvdata[3]. > > > > - The keyboard platform device was probed again from retrying the deferred > > list, by another thread `deferred_probe_work_func`. The parent's drvdata > > wasn't NULL and cros_ec_register() for the transport device weren't > > finished. The race happened. > > Hi Dmitry, > > Does it make sense to you? I'll have to research how MFD mixes up statically described and DT-described platform devices and makes sure that children are not probed before the parent is ready - I think we need to make cros_ec behave the same way. Thanks. -- Dmitry
