Re: [PATCH v2] driver core: Take parent lock in async device attach

[Johan Hovold <johan@kernel.org>]

On Wed, Oct 07, 2026 at 01:15:14PM +0000, Mario Peter wrote:
> On buses with need_parent_lock set (only USB), probe() must run with the
> parent device locked. A synchronous attach after device_add() gets this
> from the caller, e.g. usb_set_configuration() holds the udev lock while
> adding interfaces. __device_attach_async_helper() runs the probe from an
> async worker instead, where that lock isn't held, and only takes
> device_lock(dev).

> Take the parent lock in __device_attach_async_helper() as well, like
> __driver_attach_async_helper() does, and move
> __device_driver_lock/unlock() up for that. With this the warning was
> gone in 300 boots on the board and in 6000 iterations in QEMU.
> 
> Fixes: 765230b5f084 ("driver-core: add asynchronous probing support for drivers")
> Assisted-by: LLM
> Signed-off-by: Mario Peter <mario.peter@leica-geosystems.com>
> ---
> v2:
> - Describe the race in more detail
> - Keep the multi-TT detail, but say why the hub has to be multi-TT
>   for this symptom
> - Reproduce and test on v7.3-rc6 in QEMU
> 
> In the same QEMU setup, a debug-only device_lock_assert(&udev->dev) in
> usb_probe_interface() fired on every async probe of a hub interface
> without this patch (52 of 52) and never with it (0 of 102). The hub
> emulator and the test scripts are small, I can post them if that helps.

Thanks for fixing this, USB interfaces should indeed always be probed
with the parent lock held:

Reviewed-by: Johan Hovold <johan@kernel.org>

I believe we want this in stable too:

Cc: stable@vger.kernel.org

> Not covered: deferred_probe_work_func() also re-probes via
> __device_attach() without the parent lock.

Thanks for reporting this as well. I've started preparing a patch to
address it.

Johan