linux-kernel - Problem with set_current

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Message-ID: <804dabb00810150750sb54377dhc83841dedee0f72b@mail.gmail.com>
Date:	Wed, 15 Oct 2008 22:50:45 +0800
From:	"Peter Teoh" <htmldeveloper@...il.com>
To:	LKML <linux-kernel@...r.kernel.org>
Subject: Problem with set_current_state() and schedule()

I am puzzled over this:

The module just consist of three function:

static int myfunction(void)
{
       dbg("%s - enter....", __FUNCTION__);

       while (!kthread_should_stop()) {
               dbg("%s - executing....", __FUNCTION__);
               set_current_state(TASK_INTERRUPTIBLE);
               printk("sssssssssssssssssssssssssssssssss\n");


               schedule(); ======>       ////// removed for part 2
               printk("sssssssssssssssssssssssssssssssss\n");======>//////
removed for part 2


               msleep(1000);
               schedule();
       }
       return 0;
       dbg("%s exit", __FUNCTION__);
}

int init_module(void)
{

       g_task = kthread_run(myfunction, NULL, "mykthread");

       return 0;
}

void cleanup_module(void)
{
       printk(KERN_INFO "Goodbye mykthread.\n");
       kthread_stop(g_task);
}

Below is the dmesg out .... noticed two parts (based on timing output):

Part 1:
[ 1160.348000] mykthread: myfunction - enter....
[ 1160.348000] mykthread: myfunction - executing....
[ 1160.348000] sssssssssssssssssssssssssssssssss
[ 1208.632000] Goodbye mykthread.=======> this is because I "rmmod",
otherwise it got stuck in the previous statement.

Part 2:
[ 1208.632000] sssssssssssssssssssssssssssssssss
[ 1225.612000] mykthread: myfunction - enter....
[ 1225.612000] mykthread: myfunction - executing....
[ 1225.612000] sssssssssssssssssssssssssssssssss
[ 1226.616000] mykthread: myfunction - executing....
[ 1226.616000] sssssssssssssssssssssssssssssssss
[ 1227.620000] mykthread: myfunction - executing....
[ 1227.620000] sssssssssssssssssssssssssssssssss
[ 1228.624000] mykthread: myfunction - executing....
[ 1228.624000] sssssssssssssssssssssssssssssssss
[ 1229.628000] mykthread: myfunction - executing....
[ 1229.628000] sssssssssssssssssssssssssssssssss
[ 1230.632000] mykthread: myfunction - executing....
[ 1230.632000] sssssssssssssssssssssssssssssssss
[ 1231.636000] mykthread: myfunction - executing....
[ 1231.636000] sssssssssssssssssssssssssssssssss
[ 1232.640000] mykthread: myfunction - executing....
[ 1232.640000] sssssssssssssssssssssssssssssssss
[ 1233.644000] mykthread: myfunction - executing....
[ 1233.644000] sssssssssssssssssssssssssssssssss
[ 1234.648000] mykthread: myfunction - executing....
[ 1234.648000] sssssssssssssssssssssssssssssssss
[ 1235.652000] mykthread: myfunction - executing....
[ 1235.652000] sssssssssssssssssssssssssssssssss
[ 1236.656000] mykthread: myfunction - executing....
[ 1236.656000] sssssssssssssssssssssssssssssssss
[ 1237.660000] mykthread: myfunction - executing....
[ 1237.660000] sssssssssssssssssssssssssssssssss
[ 1238.664000] mykthread: myfunction - executing....
[ 1238.664000] sssssssssssssssssssssssssssssssss
[ 1239.668000] mykthread: myfunction - executing....
[ 1239.668000] sssssssssssssssssssssssssssssssss
[ 1240.672000] mykthread: myfunction - executing....
[ 1240.672000] sssssssssssssssssssssssssssssssss
[ 1241.676000] mykthread: myfunction - executing....
[ 1241.676000] sssssssssssssssssssssssssssssssss
[ 1242.680000] mykthread: myfunction - executing....
[ 1242.680000] sssssssssssssssssssssssssssssssss

For part 1:

After printing one line, the program never seemed to continue anymore.
  why?   It got stuck in the first schedule().

For part 2:

Just remove the "remove for part 2".   And u can immediately see that
it starts to loop forever.   So effectively there is only one
schedule() in the while loop.

Why?

I am quite puzzled......thanks in advance for the help.   :-).

-- 
Regards,
Peter Teoh
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