Hi all,
I believe a bug has been introduced in recent Linux kernels that
causes udev rules to not be applied when the system is overloaded with
other tasks. This is more easily seen on single core machines since
it is easier to overload the system.
My goal is to give all users read and write permissions to a USB
device. To more easily reproduce the problem, I used a pre-existing
hardware test circuit where I can automatically plug and unplug a USB
device through software control. At the same time I had the OS
writing a large file over NFS with the "dd" command and performing
other tasks if needed. Intermittently, my permissions were not being
properly set by udev. Everything else about the enumeration process
with the device was correct.
I am using an un-programmed Cypress microcontroller as my device.
These devices have a VID of 0x04B4 and a PID of 0x8613. Therefore, my
udev rules file /etc/udev/rules.d/99-test.rules is simply:
ACTION=="add", SUBSYSTEMS=="usb", ATTRS{idVendor}=="04b4",
ATTRS{idProduct}=="8613", MODE="0666"
The problem appears under kernel 2.6.25.6 and 2.6.25.9 on different
motherboards. It can also be reproduced (albeit intermittently) when
manually attaching USB devices to the system, as opposed to using my
convenient automated hardware circuit. The same behavior was also
observed with a full-speed device.
I have tried this on kernel 2.6.23.1 and found that this was not
susceptible to this issue. I have also tried 118 and 124 versions of
udev, and found that these particular versions of udev had no effect
on the pass/failure rate of the test.
Any help would be much appreciated.
Best regards,
-Leonid
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