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

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Message-ID: <CAMz4ku+WWGCT+ZSWeqptpzu5V5hR7wJS1q=ov7KiUav0QYJULQ@mail.gmail.com>
Date:   Tue, 3 Jan 2017 20:21:22 +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

On 28 December 2016 at 20:30, Janusz Dziedzic <janusz.dziedzic@...il.com> wrote:
> 2016-12-27 13:16 GMT+01:00 Baolin Wang <baolin.wang@...aro.org>:
>> 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.
>>>
> Probably you have little bit different code than current community
> version (depends how your PM works).
>
> This is possible when we write:
> dwc3_writel(dwc->regs, DWC3_GEVNTCOUNT(0), 0);
> And after that
> dwc3_writel(dwc->regs, DWC3_GEVNTCOUNT(0), 4);
>
> After that we will get 0xFFFC (-4).
>
> Possible races:
> 1) dwc3_event_buffers_setup/dwc3_event_buffers_cleanup - write 0
> 2) dwc3_thread - write 4
>
> While [1] could be called in PM work or UM context (init in Android
> case) spin_lock_irqsave() will only disable local irqs and still we
> could get IRQ on different core, next update evt->count and run
> thread...

Yeah, that's the possible races.

>
> So, seems your patch will solve this.
>
> I am not sure this problem could be also visible in community current version.
>
> Anyway, thanks for handling this.
>
> BR
> Janusz
>>> 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
>
>
>
> --
> Janusz Dziedzic



-- 
Baolin.wang
Best Regards