On 10-01-08 16:33, Nikolay N. Ivanov wrote:
I'm really newbie in kernel programming but I fond of daring experiments.
So I have written a simple module which is runs infinite cycle in the
init function. After insmodding system hangs up (it is not a problem
because i use qemu). I also tryed to put endless loop into exit function.
Then I've written a script.
#!/bin/sh
sleep 20 rmmod -f hangupmodule
I run this script every time before insmodding (or rmmodding). But
nothing helps to remain the system into working state. So my [stupid]
question is whether the system really hangs up when endless cycle runs
inside init or exit function?
Depends on CONFIG_PREEMPT.
Having a non-preemtive kernel means (by definition) that processes can not
be scheduled away while running in kernel-mode -- in this case the insmod
process is running in kernel-mode inside your infite loop and will be the
only process that runs, effectively locking up the machine (interrupts will
still happen but nothing will come of it).
With a preemptive kernel though, the system will happily switch away from
insmod to different processes, allowing you to cleanly reboot to get rid of
the insmod process -- you can't kill it since it's in kernel-mode.
Rene.
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