Netdev Archive on lore.kernel.org
help / color / mirror / Atom feed
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

  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
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=7d26fa0f-3a45-cefc-fd83-e8979ba6107c@canonical.com \
    --to=krzysztof.kozlowski@canonical.com \
    --cc=andreyknvl@gmail.com \
    --cc=balbi@kernel.org \
    --cc=gregkh@linuxfoundation.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=netdev@vger.kernel.org \
    --cc=paskripkin@gmail.com \
    --cc=stern@rowland.harvard.edu \
    --cc=syzbot+abd2e0dafb481b621869@syzkaller.appspotmail.com \
    --cc=syzkaller-bugs@googlegroups.com \
    --cc=thierry.escande@collabora.com \
    --subject='Re: [syzbot] INFO: task hung in port100_probe' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).