Re: BUG with linux 5.9.0 with dwc3 in gadget mode

[Ferry Toth <fntoth@gmail.com>]

Op 21-10-2020 om 03:56 schreef Thinh Nguyen:
> Jack Pham wrote:
>> Hi Thinh, Ferry,
>>
>> On Tue, Oct 20, 2020 at 10:58:31PM +0000, Thinh Nguyen wrote:
>>> Thinh Nguyen wrote:
>>>> Hi,
>>>>
>>>> Ferry Toth wrote:
>>>>> Op 20-10-2020 om 14:32 schreef Felipe Balbi:
>>>>>> Hi,
>>>>>>
>>>>>> Ferry Toth <fntoth@gmail.com> writes:
>>>>>>
>>>>>> 8< snip
>>>>>>
>>>>>>>>> [   12.657416] CR2: 0000000100000000
>>>>>>>>> [   12.660729] ---[ end trace 9b92dea6da33c71e ]---
>>>>>>>> It this something you can reproduce on your end? Ferry, can you get
>>>>>>>> dwc3
>>>>>>>> trace logs when this happens? ftrace_dump_on_oops may help here.
>>>>>>> I will do that tonight. Is flipping on ftrace_dump_on_oops
>>>>>>> sufficient or
>>>>>>> do I need to do more?
>>>>>> you'd have to enable dwc3 trace events first ;-)
>>>>>>
>>>>>>> BTW after posting this I found in host mode dwc3 is not working
>>>>>>> properly
>>>>>>> either. No oops, but no driver get loaded on device plug in.
>>>>>> okay
>>>>>>
>>>>> Ehem, you maybe only me to enable /dwc3/dwc3_ep_dequeue/enable:
>>>>>
>>>>> root@edison:/boot# uname -a
>>>>> Linux edison 5.9.0-edison-acpi-standard #1 SMP Mon Oct 19 20:17:04 UTC
>>>>> 2020 x86_64 x86_64 x86_64 GNU/Linux
>>>>> root@edison:/boot# echo 1 >
>>>>> /sys/kernel/debug/tracing/events/dwc3/dwc3_ep_dequeue/enable
>>>>> root@edison:/boot# echo 1 > /proc/sys/kernel/ftrace_dump_on_oops
>>>>> root@edison:/boot#
>>>>> root@edison:/boot# [ 2608.585323] BUG: kernel NULL pointer
>>>>> dereference, address: 0000000000000000
>>>>> [ 2608.592288] #PF: supervisor read access in kernel mode
>>>>> [ 2608.597419] #PF: error_code(0x0000) - not-present page
>>>>> [ 2608.602549] PGD 0 P4D 0
>>>>> [ 2608.605090] Oops: 0000 [#1] SMP PTI
>>>>> [ 2608.608580] CPU: 1 PID: 733 Comm: irq/15-dwc3 Not tainted
>>>>> 5.9.0-edison-acpi-standard #1
>>>>> [ 2608.616571] Hardware name: Intel Corporation Merrifield/BODEGA BAY,
>>>>> BIOS 542 2015.01.21:18.19.48
>>>>> [ 2608.625356] RIP: 0010:dwc3_gadget_ep_dequeue+0x41/0x1c0
>>>>> [ 2608.630580] Code: e9 51 01 00 00 4c 8d a3 30 01 00 00 4c 89 e7 e8
>>>>> 15 e6 42 00 49 8b 4e 48 49 89 c5 49 8d 46 48 48 8d 51 a0 48 39 c8 75
>>>>> 0f eb 2e <48> 8b 4a 60 48 8d 51 a0 48 39 c8 74 21 48 39 d5 75 ee 45 31
>>>>> f6 4c
>>>>> [ 2608.649320] RSP: 0018:ffffa838002a7c40 EFLAGS: 00010087
>>>>> [ 2608.654543] RAX: ffff9a5f4609c048 RBX: ffff9a5f46f48028 RCX:
>>>>> 0000000000000000
>>>>> [ 2608.661666] RDX: ffffffffffffffa0 RSI: 0000000000000008 RDI:
>>>>> ffff9a5f46f48158
>>>>> [ 2608.668790] RBP: ffff9a5f7bd09b40 R08: 00000000000002d8 R09:
>>>>> ffff9a5f7dd6a000
>>>>> [ 2608.675913] R10: ffffa838002a7d90 R11: ffff9a5f46f48300 R12:
>>>>> ffff9a5f46f48158
>>>>> [ 2608.683039] R13: 0000000000000046 R14: ffff9a5f4609c000 R15:
>>>>> ffff9a5f7ad77e00
>>>>> [ 2608.690165] FS:  0000000000000000(0000) GS:ffff9a5f7e300000(0000)
>>>>> knlGS:0000000000000000
>>>>> [ 2608.698244] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>>>> [ 2608.703980] CR2: 0000000000000000 CR3: 000000003780a000 CR4:
>>>>> 00000000001006e0
>>>>> [ 2608.711102] Call Trace:
>>>>> [ 2608.713561]  usb_ep_dequeue+0x19/0x80
>>>>> [ 2608.717234]  u_audio_stop_capture+0x54/0x9a [u_audio]
>>>>> [ 2608.722289]  afunc_set_alt+0x73/0x80 [usb_f_uac2]
>>>> I took a look at how the audio function is handling switching alternate
>>>> setting and dequeuing endpoints, and I think I found the issue.
>>>>
>>>> Here's a snippet of the free_ep() code in u_audio.c:
>>>>
>>>> static inline void free_ep(struct uac_rtd_params *prm, struct usb_ep *ep)
>>>> {
>>>>      .....
>>>>          for (i = 0; i < params->req_number; i++) {
>>>>                  if (prm->ureq[i].req) {
>>>>                          usb_ep_dequeue(ep, prm->ureq[i].req);
>>>>                          usb_ep_free_request(ep, prm->ureq[i].req);
>>>>                          prm->ureq[i].req = NULL;
>>>>                  }
>>>>          }
>>>>    ....
>>>>
>>>>
>>>> usb_ep_dequeue() can be asynchronous. The dwc3 still has ownership of
>>>> the request until it gives back the request. Freeing the request
>>>> immediately here will cause a problem.
>>> To confirm my suspicion, can you try this and see if you still get oops?
>>>
>>> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
>>> index eec8e9a9e3ed..b66eb24ec070 100644
>>> --- a/drivers/usb/dwc3/gadget.c
>>> +++ b/drivers/usb/dwc3/gadget.c
>>> @@ -2031,6 +2031,7 @@ static int dwc3_gadget_ep_dequeue(struct usb_ep *ep,
>>>                          list_for_each_entry_safe(r, t,
>>> &dep->started_list, list)
>>>                                  dwc3_gadget_move_cancelled_request(r);
>>>   
>>> +                       dwc3_gadget_ep_cleanup_cancelled_requests(dep);
>>>                          goto out;
>>>                  }
>>>          }
>>>
>>>
>>> This will make usb_ep_dequeue() synchronous. (Note that this is not tested).
>> But only for dwc3 right? In general do other UDC drivers provide
>> synchronous behavior? It does states clearly in the kerneldoc for
>> usb_ep_dequeue() that the completion is asynchronous.  From
>> drivers/usb/gadget/udc/core.c:
>>
>>   * If the request is still active on the endpoint, it is dequeued and
>>   * eventually its completion routine is called (with status -ECONNRESET);
>>   * else a negative error code is returned.  This routine is asynchronous,
>>   * that is, it may return before the completion routine runs.
>>
>> Alternatively, could we not fix up u_audio.c to deal with this?
> 
> The issue is in u_audio.c. But I want to confirm my suspicion about
> whether the oops that Ferry is due to this (most likely it is).

When I disable uac2 from my config this oops goes away.
But I also have have eem (ethernet), which appears and then drops away.
So, seems there are more things wrong.

> We don't want to apply this as a workaround and mask the issue in audio.c.
> 
>>
>> diff --git a/drivers/usb/gadget/function/u_audio.c b/drivers/usb/gadget/function/u_audio.c
>> index 56906d15fb55..f08f036d520e 100644
>> --- a/drivers/usb/gadget/function/u_audio.c
>> +++ b/drivers/usb/gadget/function/u_audio.c
>> @@ -89,7 +89,12 @@ static void u_audio_iso_complete(struct usb_ep *ep, struct usb_request *req)
>> 	struct snd_uac_chip *uac = prm->uac;
>>
>> 	/* i/f shutting down */
>> -	if (!prm->ep_enabled || req->status == -ESHUTDOWN)
>> +	if (!prm->ep_enabled) {
>> +		usb_ep_free_request(ep, req);
>> +		return;
>> +	}
>> +
>> +	if (req->status == -ESHUTDOWN)
>> 		return;
>>
>> 	/*
>> @@ -352,7 +357,6 @@ static inline void free_ep(struct uac_rtd_params *prm, struct usb_ep *ep)
>> 	for (i = 0; i < params->req_number; i++) {
>> 		if (prm->ureq[i].req) {
>> 			usb_ep_dequeue(ep, prm->ureq[i].req);
>> -			usb_ep_free_request(ep, prm->ureq[i].req);
>> 			prm->ureq[i].req = NULL;
>> 		}
>> 	}
>>
>> Jack
> 
> Yes, the u_audio.c needs to do something like that.
> 
> BR,
> Thinh
>