Re: [PATCH] usb: dwc3: ep0: Fix the possible missed request for handling delay STATUS phase

[Felipe Balbi]

Hi,

Baolin Wang <baolin.wang@xxxxxxxxxx> writes:
>>>>>> Baolin Wang <baolin.wang@xxxxxxxxxx> 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@xxxxxxxxxx>
>>>>>>> ---
>>>>>>>  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.
>>
>> not only mass storage. It needs to be done for all drivers. The way to
>> do that is to teach functions that control transfers are composed of two
>> or three phases. If you look at UDC drivers today, they all have
>> peculiarities about control transfers to handle stuff that *maybe*
>> gadget drivers won't handle.
>>
>> What we should do here is make sure that *all* 3 phases always have a
>> matching usb_ep_queue() coming from the upper layers. Whether
>> composite.c or f_*.c handles it, that's an implementation detail. But
>> just to illustrate the problem, we should be able to get rid of
>> dwc3_ep0_out_start() and assume that the upper layer will call
>> usb_ep_queue() when it wants to receive a new SETUP packet.
>>
>> Likewise, we should be able to assume that STATUS phase will only start
>> based on a usb_ep_queue() call. That way we can remove
>> USB_GADGET_DELAYED_STATUS altogether, because that will *always* be the
>> case. There will be no races to handle apart from the normal case where
>> XferNotReady can come before or after usb_ep_queue(), but we already
>> have proper handling for that too.
>
> Thanks to explain, but seems it need lots of work to convert these
> drivers, and I saw Alan had some concern about that. So I am not sure
> how to convert these drivers which can meet your requirements, maybe
> from adding one "wants_explicit_ctrl_phases"  flag in struct
> usb_gadget as you suggested to start?

yeah. Something like this:

patch 1: add the new flag and document it
patch 2: implement usb_ep_queue() for data and status phases conditional
	to that flag being set
patch 3: (e.g.) change dwc3 to rely on that behavior and pass the flag
	to usb_gadget.

this will be enough to actually test that the idea and implementation
works out. After that, just for_each_UDC_driver() port_patch_3(); Then
you add:

patch N - 1: remove legacy code and force behavior of
	wants_explicit_ctrl_phases
patch N: remove wants_explicit_ctrl_phases

something along these lines.

-- 
balbi

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