Messages in this thread | | | From | Krzysztof Kozlowski <> | Subject | Re: [syzbot] INFO: task hung in port100_probe | Date | Mon, 25 Oct 2021 16:57:23 +0200 |
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On 21/10/2021 00:05, Alan Stern wrote: >> >> The syzkaller reproducer fails if >1 of threads are running these usb >> gadgets. When this happens, no "in_urb" completion happens. No this >> "ack" port100_recv_ack(). >> >> I added some debugs and simply dummy_hcd dummy_timer() is woken up on >> enqueuing in_urb and then is looping crazy on a previous URB (some older >> URB, coming from before port100 driver probe started). The dummy_timer() >> loop never reaches the second "in_urb" to process it, I think. > > Is there any way you can track down what's happening in that crazy loop? > That is, what driver was responsible for the previous URB? > > We have seen this sort of thing before, where a driver submits an URB > for a gadget which has disconnected. The URB fails with -EPROTO status > but the URB's completion handler does an automatic resubmit. That can > lead to a very tight loop with dummy-hcd, and it could easily prevent > some other important processing from occurring. The simple solution is > to prevent the driver from resubmitting when the completion status is > -EPROTO.
Hi Alan,
Thanks for the reply.
The URB which causes crazy loop is the port100 driver second URB, the one called ack or in_urb.
The flow is: 1. probe() 2. port100_get_command_type_mask() 3. port100_send_cmd_async() 4. port100_send_frame_async() 5. usb_submit_urb(dev->out_urb) The call succeeds, the dummy_hcd picks it up and immediately ends the timer-loop with -EPROTO
The completion here does not resubmit another/same URB. I checked this carefully and I hope I did not miss anything.
6. port100_submit_urb_for_ack() which sends the in_urb: usb_submit_urb(dev->in_urb) ... wait for completion ... dummy_hcd loops on this URB around line 2000: if (status == -EINPROGRESS) continue
Best regards, Krzysztof
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