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

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Date:   Tue, 27 Dec 2016 19:06:46 +0800
From:   Baolin Wang <baolin.wang@...aro.org>
To:     Janusz Dziedzic <janusz.dziedzic@...il.com>
Cc:     Felipe Balbi <balbi@...nel.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

Hi,

On 27 December 2016 at 18:52, Janusz Dziedzic <janusz.dziedzic@...il.com> wrote:
> 2016-12-26 9:01 GMT+01:00 Baolin Wang <baolin.wang@...aro.org>:
>> 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.
>>
> Interesting, I always think we mask interrupt in dwc3_interrupt() by setting
> DWC3_GEVNTSIZ_INTMASK
> And unmask interrupt when we end dwc3_thread_interrupt().
>
> So, we shouldn't get any IRQ from HW during dwc3_thread_interrupt(),
> or I miss something?
> Do you have some traces that indicate this masking will not work correctly?

Yes, but we just masked the interrupts described in DEVTEN register,
and we did not mask all the interrupts, like the endpoint command
complete event, transfer complete event and so on, so we can still get
interrupts.

>
> BTW, what value you get when problem occured, 0xFFFC?

Yes, something like this, the event count become huge.

>
> BR
> Janusz
>
>> Signed-off-by: Baolin Wang <baolin.wang@...aro.org>
>> ---
>>  drivers/usb/dwc3/gadget.c |    6 +++++-
>>  1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
>> index 6785595..1a1e1f4 100644
>> --- a/drivers/usb/dwc3/gadget.c
>> +++ b/drivers/usb/dwc3/gadget.c
>> @@ -2894,10 +2894,13 @@ static irqreturn_t dwc3_check_event_buf(struct dwc3_event_buffer *evt)
>>                 return IRQ_HANDLED;
>>         }
>>
>> +       spin_lock(&dwc->lock);
>>         count = dwc3_readl(dwc->regs, DWC3_GEVNTCOUNT(0));
>>         count &= DWC3_GEVNTCOUNT_MASK;
>> -       if (!count)
>> +       if (!count) {
>> +               spin_unlock(&dwc->lock);
>>                 return IRQ_NONE;
>> +       }
>>
>>         evt->count = count;
>>         evt->flags |= DWC3_EVENT_PENDING;
>> @@ -2914,6 +2917,7 @@ static irqreturn_t dwc3_check_event_buf(struct dwc3_event_buffer *evt)
>>                 memcpy(evt->cache, evt->buf, count - amount);
>>
>>         dwc3_writel(dwc->regs, DWC3_GEVNTCOUNT(0), count);
>> +       spin_unlock(&dwc->lock);
>>
>>         return IRQ_WAKE_THREAD;
>>  }
>> --
>> 1.7.9.5
>>
>> --
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>
>
>
> --
> Janusz Dziedzic



-- 
Baolin.wang
Best Regards