This a problem that occurs under Linux 2.4.5-ac9 with the USB core
code compiled in, but usb-uhci, usb-storage, and sd_mod compiled
as modules. This setup allows me to offload images from a HP 315
USB digital camera. The problem may exist in earlier 2.4.x kernels
but this is the first time I've noticed it.
I insert all the above modules, turn on the camera, mount it's
CompactFlash card msdos filesystem that appears on /dev/sda1, and
then can offload the images with the cp command. Then I unmount
/dev/sda1, turn off the camera, and remove the modules. The usb-uhci
is removed nicely, but processes associated with the usb-storage and
sd_mod modules become zombies. Every time this procedure is repeated
there is another such zombie pair created. The usb-uhci module has
no process associated with it.
These processes appear to be children of kusbd, a process which seems
to be generated by the compiled in USB core. That's what the "ps -fA
--forest" command shows, and doing "kill -HUP $(pidof kusbd)" removes
the zombies but also causes kusbd to become a zombie. After that the
camera can't be mounted by reinserting the modules. Reboot seems to be
the only cure.
When the camera is successfully mounted doing "lsmod" shows usb-storage
and sd_mod as being used, but not usb-uhci. It's been suggested to me
that the zombie problem is likely caused by a bug in kusbd, but I'd add
that it seems to me that usb-uhci may also be a candidate for delousing.
I'd appreciate some comments as to why zombie processes are created by
removing modules and/or how to prevent it, even any that can suggest
something dumb that I'm doing to cause it to happen. I can provide
more details if they are needed.
---
Clifford Kite Not a guru. (tm)
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