linux-kernel - Re: [PATCH] usb: dwc3: gadget: Avoid race between dwc3 interrupt handler and irq thread handler

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Date:   Fri, 6 Jan 2017 10:44:03 +0800
From:   Baolin Wang <baolin.wang@...aro.org>
To:     John Youn <John.Youn@...opsys.com>
Cc:     Felipe Balbi <balbi@...nel.org>,
        Janusz Dziedzic <janusz.dziedzic@...il.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        USB <linux-usb@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linaro Kernel Mailman List <linaro-kernel@...ts.linaro.org>,
        Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH] usb: dwc3: gadget: Avoid race between dwc3 interrupt
 handler and irq thread handler

Hi John,

On 6 January 2017 at 03:08, John Youn <John.Youn@...opsys.com> wrote:
> On 12/28/2016 5:29 PM, John Youn wrote:
>>
>>
>>> Janusz Dziedzic <janusz.dziedzic@...il.com> writes:
>>>>>>> On some platfroms(like x86 platform), when one core is running the
>>> USB gadget
>>>>>>> irq thread handler by dwc3_thread_interrupt(), meanwhile another
>>> core also can
>>>>>>> respond other interrupts from dwc3 controller and modify the event
>>> buffer by
>>>>>>> dwc3_interrupt() function, that will cause getting the wrong event
>>> count in
>>>>>>> irq thread handler to make the USB function abnormal.
>>>>>>>
>>>>>>> We should add spin_lock/unlock() in dwc3_check_event_buf() to avoid
>>> this race.
>>>>>>
>>>>>> Why not spin_lock_irq ones? This lock seems to be used in both
>>>>>> normal and interrupt threads. Or, I missed anything?
>>>>>
>>>>> this is top half handler. Interrupts are already disabled.
>>>>>
>>>> BTW,
>>>> We don't use spin_lock in top half handler.
>>>> Maybe we should/can switch all spin_lock_irqsave() to simple
>>>> spin_lock() in the thread/callbacks?
>>>
>>> in theory, yes we've masked all interrupts from this controller for the
>>> duration of the thread handler. However this breaks networking
>>> gadgets. I can only guess network stack has a hard requirement to run
>>> with IRQs disabled.
>>>
>>
>> Hi,
>>
>> Is this version 3.00a of the core?
>>
>> That version has a STAR where the interrupts cannot be masked. That
>> results in similar symptoms to what you're seeing here.

Sorry for late reply. The version is 2.80a.

>> Regards,
>> John
>>
>
> Didn't see any response to this. Just want to make sure this
> possibility is addressed as there is a workaround for it on mainline.

Thanks for reminding.

>
> See the following commits for details:
>
> d9fa4c63f766 ("usb: dwc3: core: add a event buffer cache")
> ebbb2d59398f ("usb: dwc3: gadget: use evt->cache for processing events")
> 65aca3205046 ("usb: dwc3: gadget: clear events in top-half handler")
> cf40b86b6ef6 ("usb: dwc3: Implement interrupt moderation")
> 28632b44d129 ("usb: dwc3: Workaround for irq mask issue")
>

-- 
Baolin.wang
Best Regards