Re: [PATCH] usb: dwc3: Potential fix of possible dwc3 interrupt storm

[Selvarasu Ganesan <selvarasu.g@samsung.com>]

On 9/13/2024 11:30 PM, Thinh Nguyen wrote:
> On Fri, Sep 13, 2024, Thinh Nguyen wrote:
>> On Fri, Sep 13, 2024, Selvarasu Ganesan wrote:
>>> Hi Thinh,
>>>
>>> So far, there have been no reported error instances. But, we suspecting
>>> that the issue may be related to our glue driver. In our glue driver, we
>>> access the reference of evt->flags when starting or stopping the gadget
>>> based on a VBUS notification. We apologize for sharing this information
>>> so late, as we only became aware of it recently.
>>>
>>> The following sequence outlines the possible scenarios of race conditions:
>>>
>>> Thread#1 (Our glue Driver Sequence)
>>> ===================================
>>> ->USB VBUS notification
>>> ->Start/Stop gadget
>>> ->dwc->ev_buf->flags |= BIT(20); (It's for our reference)
>>> ->Call dwc3 exynos runtime suspend/resume
>>> ->dwc->ev_buf->flags &= ~BIT(20);
>>> ->Call dwc3 core runtime suspend/resume
>>>
>>> Thread#2
>>> ========
>>> ->dwc3_interrupt()
>>> ->evt->flags |= DWC3_EVENT_PENDING;
>>> ->dwc3_thread_interrupt()
>>> ->evt->flags &= ~DWC3_EVENT_PENDING;
>>>
>> This is great! That's likely the problem. Glad you found it.
>>
>>>
>>> After our internal discussions, we have decided to remove the
>>> unnecessary access to evt->flag in our glue driver. We have made these
>>> changes and initiated testing.
>>>
>>> Thank you for your help so far to understand more into our glue driver code.
>>>
>>> And We are thinking that it would be fine to reset evt->flag when the
>>> USB controller is started, along with the changes you suggested earlier.
>>> This additional measure will help prevent similar issues from occurring
>>> in the future.
>>>
>>> Please let us know your thoughts on this proposal. If it is not
>>> necessary, we understand and will proceed accordingly.
>>>
>> You can submit the change I suggested. That's a valid change. However,
>> we should not include the reset of the DWC3_EVENT_PENDING flag. Had we
>> done this, you may not found the issue above. It serves no purpose for
>> the core driver logic and will be an extra burden for us to maintain. (I
>> don't want to scratch my head in the future to figure out why that
>> change was needed or concern whether it can be removed without causing
>> regression).
>>
> Also, perhaps you may want to revisit and review the change below to see
> if the glue driver may be the culprit:
>
> 14e497183df2 ("usb: dwc3: core: Prevent USB core invalid event buffer address access")

Hi Thinh,

We reconfirmed that this issue not due to our glue driver.


Thanks,
Selva
> Thanks,
> Thinh