Re: [PATCH v2 0/8] HID: iio: Avoid race between callback setup and device exposure

[Sanjay Chitroda <sanjayembeddedse@gmail.com>]

On 23 June 2026 4:00:27 pm IST, Andy Shevchenko <andriy.shevchenko@intel.com> wrote:
>On Mon, Jun 22, 2026 at 10:59:56AM +0530, Sanjay Chitroda wrote:
>> 
>> This series avoid a race condition in HID IIO drivers related to the
>> ordering between callback registration and device exposure.
>> 
>> Currently, several HID IIO drivers register the IIO device (making it
>> visible to userspace and other kernel consumers) before all required
>> callbacks and resources are fully initialized, or rely on devm-based
>> cleanup in a way that does not guarantee correct teardown ordering.
>> This creates a window where the device can be accessed while it is
>
>There is a difference between "this creates" and "this might create".
>I believe Srinivas and others were asking for the proof. So, what path
>in the code makes this happen or possible to happen?
>
iio_device_register() exposes the IIO device to user space, while sensor_hub_register_callback() registers callbacks for buffered IIO(streaming mode).

This might create window where from userspace buffer mode is enabled and callbacks are not registered which would result into loss of samples until callback registration completes, although no explicit failure. In teardown path which can resulting in stale/no data.

This was discussed in the v1 thread and v2 was posted based on discussion and agreement:
 https://lore.kernel.org/all/3FED088A-651B-4E8B-840B-1B92CB4DF6F4@gmail.com/


>> not fully initialized or is being torn down, potentially leading to
>> sample drop or stale/no data.
>> 
>> To handle this, the series ensures that:
>>   - All required callbacks and resources are set up before the device
>>     is registered with the IIO core
>>   - Resource cleanup is performed explicitly where ordering matters
>> 
>> PS: This is prepratory series to convert all HID IIO driver to devm.
>> 
>> Testing:
>>   - Compiled with W=1 for each patch in series
>> 
>> ---
>> Changes in v2:
>> - Drop fixes tag and rectify commit message with reference to that
>
>You also dropped my tag. Why?
>
Thank you for the review and tag on v1.

While code changes are intact in v2, the rational and commit message were updated substantially. Since commit message is as important as change which will be permanent in history for future reference, I chose to drop the tag to request a fresh review.

I shall highlight the same in change log. I'll make sure to note in future revision.

Thanks, Sanjay

>> - Link to v1: https://patch.msgid.link/20260606-5-june-hid-iio-race-fixes-v1-0-27a848c5758f@gmail.com
>