LIBUSB_ERROR_TIMEOUT where libusb seems to get stuck for roughly 168 seconds

[azlamzn]

OS:

Ubuntu 20.04.4 LTS

Libraries:

libusb-1.0-0/focal,now 2:1.0.23-2build1 amd64 [installed,automatic]
libccid/focal,now 1.4.31-1 amd64 [installed,automatic]
libpcsclite1/focal,now 1.8.26-3 amd64 [installed,automatic]

Background:
I have a Python application using pyscard to read data. There is a seemingly random issue where libusb gets stuck during a transmit call for about 168 seconds which results in a LIBUSB_ERROR_TIMEOUT.

I have attached libusb debug logs with converted timestamps in order to provide some background around the series of events libusb_debug_logs_12_05_2023.txt.

The issue occurs near the bottom of the file. At timestamp 2023-12-05 09:45:56 the Python application starts the transmit that ultimately times out. The error I can observe is at Dec-05 09:55:45, which is a time period where the device is unresponsive. The logs end with unplugging the device and the issue is resolved once the device is replugged.

Question:
I wanted to confirm if this timeout behavior for 168 seconds is a known pattern and what the recommended recovery path should be since a usb reset from the Python code does not help. Thank you so much!

[tormodvolden]

I don't know where the 168 seconds come from but I see in the log:
[add_to_flying_list arm timerfd for timeout in 167723ms (first in line)
and these show up long before the issue occurs. What is the timeout that you specify, if any?

Would it be possible for you try 1.0.27-rc1 and also updated pyusb?

[azlamzn]

Thanks for the quick response! Which version of pyusb are you referring to here (I am using 1.2.1)?

[tormodvolden]

So you are not using the stock python3-usb package then. Well, you can try latest pyusb git master, but I don't think anything relevant changed since 1.2.1.

OTOH a lot changed in libusb since 1.0.23. So if we are going to debug this further we need to use latest libusb git or RC.

[rubygoldbergmachineinc]

Thanks @tormodvolden. Is the latest version for libusb backward compatible with python 3.8?

[mcuee]

Thanks @tormodvolden. Is the latest version for libusb backward compatible with python 3.8?

Yes.