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

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Message-ID: <0ac76b9b-c12b-866b-f76e-99380b7126fd@synopsys.com>
Date:   Thu, 5 Jan 2017 11:08:32 -0800
From:   John Youn <John.Youn@...opsys.com>
To:     Felipe Balbi <balbi@...nel.org>,
        Janusz Dziedzic <janusz.dziedzic@...il.com>
CC:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Baolin Wang <baolin.wang@...aro.org>,
        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

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.
> 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.

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")

Regards,
John