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Date:   Mon, 16 Jan 2017 20:00:32 +0800
From:   Baolin Wang <baolin.wang@...aro.org>
To:     Felipe Balbi <balbi@...nel.org>
Cc:     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: ep0: Fix the possible missed request for
 handling delay STATUS phase

Hi,

On 16 January 2017 at 19:29, Felipe Balbi <balbi@...nel.org> wrote:
>
> Hi,
>
> Baolin Wang <baolin.wang@...aro.org> writes:
>> Hi,
>>
>> On 16 January 2017 at 18:56, Felipe Balbi <balbi@...nel.org> wrote:
>>>
>>> Hi,
>>>
>>> Baolin Wang <baolin.wang@...aro.org> writes:
>>>> When handing the SETUP packet by composite_setup(), we will release the
>>>> dwc->lock. If we get the 'USB_GADGET_DELAYED_STATUS' result from setup
>>>> function, which means we need to delay handling the STATUS phase.
>>>
>>> this sentence needs a little work. Seems like it's missing some
>>> information.
>>>
>>> anyway, I get that we release the lock but...
>>>
>>>> But during the lock release period, maybe the request for handling delay
>>>
>>> execution of ->setup() itself should be locked. I can see that it's only
>>> locked for set_config() which is rather peculiar.
>>>
>>> What exact request you had when you triggered this? (Hint: dwc3
>>> tracepoints print out ctrl request bytes). IIRC, only set_config() or
>>> f->set_alt() can actually return USB_GADGET_DELAYED_STATUS.
>>
>> Yes, when host set configuration for mass storage driver, it can
>> produce this issue.
>>
>>>
>>> Which gadget driver were you using when you triggered this?
>>
>> mass storage driver. When host issues the setting config request, we
>> will get USB_GADGET_DELAYED_STATUS result from
>> set_config()--->fsg_set_alt(). Then the mass storage driver will issue
>> one thread to complete the status stage by ep0_queue() (this thread
>> may be running on another core), then if the thread issues ep0_queue()
>> too fast before we get the dwc->lock in dwc3_ep0_delegate_req() or
>> before we get into the STATUS stage, then we can not handle this
>> request for the delay STATUS stage in dwc3_gadget_ep0_queue().
>>
>>>
>>> Another point here is that the really robust way of fixing this is to
>>> get rid of USB_GADGET_DELAYED_STATUS altogether and just make sure
>>> gadget drivers know how to queue requests for all three phases of a
>>> Control Transfer.
>>>
>>> A lot of code will be removed from all gadget drivers and UDC drivers
>>> while combining all of it in a single place in composite.c.
>>>
>>> The reason I'm saying this is that other UDC drivers might have similar
>>> races already but they just haven't triggered.
>>
>> Yes, maybe.
>>
>>>
>>>> STATUS phase has been queued into list before we set 'dwc->delayed_status'
>>>> flag or entering 'EP0_STATUS_PHASE' phase, then we will miss the chance
>>>> to handle the STATUS phase. Thus we should check if the request for delay
>>>> STATUS phase has been enqueued when entering 'EP0_STATUS_PHASE' phase in
>>>> dwc3_ep0_xfernotready(), if so, we should handle it.
>>>>
>>>> Signed-off-by: Baolin Wang <baolin.wang@...aro.org>
>>>> ---
>>>>  drivers/usb/dwc3/ep0.c |   14 ++++++++++++++
>>>>  1 file changed, 14 insertions(+)
>>>>
>>>> diff --git a/drivers/usb/dwc3/ep0.c b/drivers/usb/dwc3/ep0.c
>>>> index 9bb1f85..e689ced 100644
>>>> --- a/drivers/usb/dwc3/ep0.c
>>>> +++ b/drivers/usb/dwc3/ep0.c
>>>> @@ -1123,7 +1123,21 @@ static void dwc3_ep0_xfernotready(struct dwc3 *dwc,
>>>>               dwc->ep0state = EP0_STATUS_PHASE;
>>>>
>>>>               if (dwc->delayed_status) {
>>>> +                     struct dwc3_ep *dep = dwc->eps[0];
>>>> +
>>>>                       WARN_ON_ONCE(event->endpoint_number != 1);
>>>> +                     /*
>>>> +                      * We should handle the delay STATUS phase here if the
>>>> +                      * request for handling delay STATUS has been queued
>>>> +                      * into the list.
>>>> +                      */
>>>> +                     if (!list_empty(&dep->pending_list)) {
>>>> +                             dwc->delayed_status = false;
>>>> +                             usb_gadget_set_state(&dwc->gadget,
>>>> +                                                  USB_STATE_CONFIGURED);
>>>
>>> Isn't this patch also changing the normal case when usb_ep_queue() comes
>>> later? I guess list_empty() protects against that...
>>
>> I think it will not change other cases, we only handle the delayed
>> status and I've tested it for a while and I did not find any problem.
>
> Alright, it's important enough to fix this bug. Can you also have a look
> into dropping USB_GADGET_DELAYED_STATUS altogether? If you're too busy,
> no issues. It'll stay in my queue.

Okay, I will have a look at f_mass_storage driver to see if we can
drop USB_GADGET_DELAYED_STATUS. Thanks.

-- 
Baolin.wang
Best Regards

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