Hello
I've got some questions about kernel threads.I am writing a module
which spawns some kernel threads, which would be removed when the
module unloads. For that purpose i call kthread_stop() at module
unload time. When issuing rmmod on the module, it deadlocks at that
point (in the call to kthread_stop), and never returns.
In the thread main function the code was something like this (it's of
course simplified).
thread_main()
{
while( ! kthread_should_stop())
{
.............
wait_event_interruptible(stop_wq, kthread_should_stop() );
}
return 0;
}
So if kthread_stop() first sets the thread "closing flag", and then
calls wake_up_process(), the thread should wake up, see he should
stop, and
end the loop. That doesnt actually never happen.
I have also tried what it is done in kernel/sched.c to finish:
/* wait for kthread_stop */
set_current_state(TASK_INTERRUPTIBLE);
while (!kthread_should_stop()) {
schedule();
set_current_state(TASK_INTERRUPTIBLE);
}
__set_current_state(TASK_RUNNING);
return 0;
I have ensured it actually arrives to that point by using printks, but
when the thread goes to sleep, it does never wake up again, so the
call to kthread_stop() lasts forever.
I dont know why this happens. Is the module cleanup code in the
context of a user process just like system calls? Can that code sleep?
If it can't sleep then the answer would be quite easy: kthread_stop()
wakes up the processes and then waits for the threads to finish (on
call wait_for_completion), but doesnt actually let them execute,
because it cannot sleep, so it deadlocks.
So I would be grateful if anyone can help me in this matter.
Regards
Aritz
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