linux-kernel - kernel threads in drivers using the RT patch

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Message-ID: <4DEA255B.2050503@unican.es>
Date:	Sat, 4 Jun 2011 14:30:19 +0200
From:	Monica Puig-Pey <puigpeym@...can.es>
To:	<linux-rt-users@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: kernel threads in drivers using the RT patch

Hello,

I'm studying how to develop drivers in a real time OS and how do they 
work. I'm using  Ubuntu 10.04 with the 2.6.31-11-rt patch installed.
I'm trying to run a kernel thread from my driver (kernel context). I 
create the kthread in the module_init, I change its real time priority 
and then make it run .
Code shown below:

thread_handler=*(struct task_struct *)kthread_create(my_tasklet_handler, 
(void*)&datos,"thread_handler");
   if (IS_ERR(&thread_handler)){
      return PTR_ERR(&thread_handler);
      printk(KERN_WARNING "<pci> (init_module)  Error creating Thread 
handler\n");
   }
params->sched_priority=20;
result = sched_setscheduler(&thread_handler, SCHED_FIFO, params);
result=wake_up_process(&thread_handler);

Params is global struct sched_param * and struct thread_handler  a 
global task_struct.

I stop the Kthread in the module_exit using 
res=kthread_stop(&thread_handler);

The kthread "thread_handler" has a while (1) loop and it is stopped in a 
semaphore, waiting for the interrupt handler. When it wakes up each time 
it calls kthread_should_stop() and depending on that break out of the 
loop or run.

My problem is, when trying to establish the rtprio kthread, the whole 
computer get blocked and I only can restart it. If I delete this part, 
then kthread runs, and works well. With the ps command I can see it has 
a 24 NON real time priority. Then the problem come when uninstalling my 
module with rmmod. In the  kthread_stop function, everything gets blocked.

Could someone tell what am I doing wrong? Or just give me some help 
about kernel threads in the RT Patch?

Thanks a lot

Mónica
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