Re: BUG with linux 5.9.0 with dwc3 in gadget mode

[Thinh Nguyen <Thinh.Nguyen@synopsys.com>]

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).

BR,
Thinh