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

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Message-ID: <CAMz4kuKyQ+H9nkCD=zZxEDCJ9Uya55_fSoa_hi0j=1f2dZx3hA@mail.gmail.com>
Date:   Tue, 27 Dec 2016 20:16:49 +0800
From:   Baolin Wang <baolin.wang@...aro.org>
To:     Felipe Balbi <balbi@...nel.org>
Cc:     Janusz Dziedzic <janusz.dziedzic@...il.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,

On 27 December 2016 at 19:11, Felipe Balbi <balbi@...nel.org> wrote:
>
> Hi,
>
> Baolin Wang <baolin.wang@...aro.org> writes:
>> 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.
>
> not true, we masked interrupts for the entire event buffer:

Yes, you are right and I missed that. I should reproduce this problem
and analyse the real reason.

>
>> static irqreturn_t dwc3_check_event_buf(struct dwc3_event_buffer *evt)
>> {
>>       struct dwc3 *dwc = evt->dwc;
>>       u32 count;
>>       u32 reg;
>>
>>       if (pm_runtime_suspended(dwc->dev)) {
>>               pm_runtime_get(dwc->dev);
>>               disable_irq_nosync(dwc->irq_gadget);
>>               dwc->pending_events = true;
>>               return IRQ_HANDLED;
>>       }
>>
>>       count = dwc3_readl(dwc->regs, DWC3_GEVNTCOUNT(0));
>>       count &= DWC3_GEVNTCOUNT_MASK;
>>       if (!count)
>>               return IRQ_NONE;
>>
>>       evt->count = count;
>>       evt->flags |= DWC3_EVENT_PENDING;
>>
>>       /* Mask interrupt */
>>       reg = dwc3_readl(dwc->regs, DWC3_GEVNTSIZ(0));
>>       reg |= DWC3_GEVNTSIZ_INTMASK;
>
> See here ?!?
>
>>       dwc3_writel(dwc->regs, DWC3_GEVNTSIZ(0), reg);
>>
>>       return IRQ_WAKE_THREAD;
>> }
>
>>> BTW, what value you get when problem occured, 0xFFFC?
>>
>> Yes, something like this, the event count become huge.
>
> please send us tracepoint data. You probably need to compress
> it. Something like 256k of trace data is probably enough, so:
>
> # mkdir -p /t
> # mount -t tracefs none /t
> # cd /t
> # echo 256 > buffer_size_kb
> # echo 1 > events/dwc3/enable
> # echo 0 > events/dwc3/dwc3_readl/enable
> # echo 0 > events/dwc3/dwc3_writel/enable
>
> (reproduce)
>
> # cp /t/trace /path/to/non-volatile/media/trace.txt

Okay, I try to do that. Thanks.

-- 
Baolin.wang
Best Regards