From: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Felipe Balbi <balbi@kernel.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
syzbot <syzbot+abd2e0dafb481b621869@syzkaller.appspotmail.com>,
linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
syzkaller-bugs@googlegroups.com,
Pavel Skripkin <paskripkin@gmail.com>,
Thierry Escande <thierry.escande@collabora.com>,
Andrey Konovalov <andreyknvl@gmail.com>
Subject: Re: [syzbot] INFO: task hung in port100_probe
Date: Mon, 25 Oct 2021 16:57:23 +0200 [thread overview]
Message-ID: <7d26fa0f-3a45-cefc-fd83-e8979ba6107c@canonical.com> (raw)
In-Reply-To: <20211020220503.GB1140001@rowland.harvard.edu>
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
next prev parent reply other threads:[~2021-10-25 14:57 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-22 15:43 [syzbot] INFO: task hung in port100_probe syzbot
2021-06-22 16:07 ` Pavel Skripkin
2021-06-22 16:21 ` syzbot
2021-07-22 14:20 ` Krzysztof Kozlowski
2021-07-22 14:23 ` Krzysztof Kozlowski
2021-07-22 14:47 ` Alan Stern
2021-07-23 9:05 ` Krzysztof Kozlowski
2021-07-23 13:07 ` Alan Stern
2021-10-20 20:56 ` Krzysztof Kozlowski
2021-10-20 22:05 ` Alan Stern
2021-10-25 14:57 ` Krzysztof Kozlowski [this message]
2021-10-25 16:22 ` Alan Stern
2021-10-25 17:13 ` Krzysztof Kozlowski
2021-10-25 18:54 ` Alan Stern
2022-03-09 19:33 ` Pavel Skripkin
2022-03-09 19:56 ` syzbot
[not found] <20220310084247.1148-1-hdanton@sina.com>
2022-03-10 14:22 ` syzbot
[not found] ` <20220311053751.1226-1-hdanton@sina.com>
2022-03-11 19:17 ` Pavel Skripkin
2022-03-11 19:18 ` syzbot
2022-03-11 19:19 ` Pavel Skripkin
2022-03-11 19:32 ` syzbot
[not found] ` <20220312005624.1310-1-hdanton@sina.com>
2022-03-12 10:36 ` Pavel Skripkin
[not found] ` <20220312115854.1399-1-hdanton@sina.com>
2022-03-12 12:44 ` Pavel Skripkin
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