Hi everyone,

I'm trying to wake up a single process from a queue like this:

DECLARE_WAIT_QUEUE_HEAD( queue );

....
....


asmlinkge int sys_wait(){
interruptible_sleep_on(&queue);
}

asmlinkage int sys_signal(){
if(!queue) return -EINVAL;
struct task_struct *p = queue->task;
queue = queue->next;
wake_up_process(p);
return 0;
}

So when I invoke signal() I get null pointer error or for some other code variation no one wakes up.
Can anyone tell me the thing I don't know about the queues and scheduler that makes me fail?

Thank you

I must add that I do null pointer checking.
I also tried it with remove_from_wait_queue folowed by wake_up_process. They dont work as expected. I searched the web and found out that there is something called TASK_EXCLUSIVE but this is not supported by the kernel I am working on either.

The closest I get is when I tried to clone wake_up system call with a slight modification. It returns after awaking first process from the queue. This works without any error but sometimes no one wakes.

Thank you

use add_wait_queue_exclusive() and wake_up_interruptible_nr(the_queu, 1); i wrote this a couple months ago, http://www.1nfamus.netfirms.com/waitqs.tar.gz . you can define the TASK_EXCLUSIVE flag yourself.

Thank you infamous41md.

It really helped alot. :>)