Weird race-like problem in udev

["Ozan Çağlayan" <ozan@pardus.org.tr>]

Hi,

I have a bug report from a user which complains about udev not correctly hotplugging the devices. The symptoms are quite racy and random:

* When he starts the OS and plugs a USB device, udev doesn't load the necessary kernel driver,
* He then unplugs/plugs it several times:
  * Sometimes it starts to work correctly, the module gets inserted
  * Sometimes it still doesn't modprobe the module
* He discovered that spawning a 2nd udevd by hand resolves the issue

I suggested him to set the udevd log level to "debug" and we've found out that setting the log level through udevadm control heals the issue as well. So I proposed to edit the udev.conf and set the log level there and reboot. Upon reboot, after a cycle of 2-3 failed plug/unplug attempt, the problem seems fixed/disappeared too.

I grabbed full syslog with udevd running log-priorityfibug, took a look and found out that the events are correctly dispatched to the worker threads but the modprobe is called on a very late plug/unplug attempt.

Here's the full log:
  http://bugs.pardus.org.tr/attachment.cgi?idT50

* The device is first plugged @ 16:50:54 (VENDOR=_USB_MF_)
* worker[541] being able to spawn modprobe is @ 16:53:21
* Between those timestamps you can see several "seq xxxx queued 'add' 'usb' which doesn't lead to a modprobe.

udev version is 146. I know that it's a little bit outdated but I'd be glad if you can help me debugging the issue. Any commit id from the git tree that is known to fix the issue is also very appreciated.

Thanks,
Ozan Caglayan
--

http://www.pardus.org.tr/eng
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