How to wait for a linux kernel thread (kthread)to exit?

Question

I have just started programing on Linux kernel threads. I have a problem which I would like to share with you guys. My code is:

void do_big_things(void *data)
{
   // do some really big things
} 
struct task_struct *t1;
struct task_struct *t2;

void calling_fucntion()
{
   for(j =0; j < 100; j++)
   {
      t1 = kthread_run(do_big_things, &data1, "thread1");
      t2 = kthread_run(do_big_things, &data2, "thread2");
   }
}

Now as far as I have concluded to this problem (I may be wrong) is that threads t1 and t2 are created and run by kernel and then program goes back at the start of loop to created and run another two threads. As there is no condition to wait for these threads to finish, the kernel creates so many threads hence causing a stack overflow.

All I want is to know that how to make program wait for these two threads to finish and then go back to loop starting another two threads.

Any help would be appreciated.

score 6 · Accepted Answer · edited Jul 17 '12 at 06:19

6

/* Wait for kthread_stop */
set_current_state(TASK_INTERRUPTIBLE);
while (!kthread_should_stop()) {
    schedule();
    set_current_state(TASK_INTERRUPTIBLE);
}

Check this article for more information: "Sleeping in the Kernel".

edited Jul 17 '12 at 06:19

Kijewski

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answered Jul 17 '12 at 06:11

Satish

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score 1 · Answer 2 · answered Nov 03 '10 at 06:50

1

Read about wait queues. This is a good place to look at.

Essentially, you need to keep track of how many threads are running (lock protected counter), and put the creating thread on a wait queue, until all threads are done. The last thread finishing its job can wake up the thread on the wait queue, so that it can repeat the process with another pair of threads.

answered Nov 03 '10 at 06:50

Sudhanshu

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My thread creating process is a kernel module. Should I put that module in a wait queue? – awatan Nov 03 '10 at 07:17
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No you put threads in the wait queue. I was just telling you the general mechanism for handling this kind of a problem. You need to find out - under what context is the calling_function running, and come up with a solution accordingly. – Sudhanshu Nov 03 '10 at 12:53
@Sudhanshu the link is broken (after 8 years kkk), do you still remember where did you get it? – campescassiano Apr 06 '18 at 08:47
I go to Wayback machine when this happens. A few months late in the reply but here it is if you or someone else is still looking: https://web.archive.org/web/20101201023051/http://book.opensourceproject.org.cn/kernel/kernelpri/opensource/0131181637/ch03lev1sec7.html – Sudhanshu Jul 16 '18 at 23:23

score 1 · Answer 3 · answered Nov 03 '10 at 12:51

1

It depends what you're doing, but you may not even want to start your own kernel threads.

You can submit a job to be run on the kernel's global workqueue using schedule_work().

If you do use your own thread you typically write it as a loop around kthread_should_stop(). Then the code which wants the thread to terminate calls kthread_stop(), which tells the thread to stop and then waits for it to stop.

answered Nov 03 '10 at 12:51

mpe

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I am interested with your`schedule_work()`can you write a code example on how to use it and wait it to complete please? – user2284570 Apr 06 '15 at 18:12

score 0 · Answer 4 · answered Feb 08 '14 at 09:20

0

YOu can also go for completions. The linux mass storage driver http://lxr.free-electrons.com/source/drivers/usb/storage/usb.c has a very good implementation of kthreads. Good Luck.

answered Feb 08 '14 at 09:20

Mitesh G

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How to wait for a linux kernel thread (kthread)to exit?

4 Answers4

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