Re: SMP driver core lock real-time driver

*Hi Doug,*



*maybe you could try to somehow tell Linux that the core is no longer
available/online. Could you try one of the following alternatives?*



*1- while the task is on the busy wait execute something like this: (where
* is the desired cpu core)*



*echo 0 > /sys/devices/system/cpu/cpu*/online*



*2- Another alternative could be to call this function *



*int cpu_down(unsigned int cpu);*



*cheers,*

*Asier.*

On Tue, Nov 21, 2017 at 3:40 AM, Doug Renton <[email protected]> wrote:

>
>  I cut and pasted a kernel module, and made it do busy work, until the
> kernel decided it had found a bug. While the busy work was going on,
> everything seemed fine, could not tell one core was busy.
>
> Everything seems to run fine with one core doing my made up task, until
> eventually the kernel decides it has found a bug.
> With the loops at something reasonable like 999, everything runs fine and
> my task ends. Once turned up to 999999, the kernel eventually gives my
> module the boot. Looks like this could be tricky. I still can't see why we
> cant just simplify everything and dedicate one/two core(s) to RTAI, and
> busy wait.
>
>
> [  189.566739] Timer module installing
> [  189.566743] Starting timer to fire in 200ms (4294939693)
> [  189.763714] my_timer_callback called (4294939743).
> [  216.060934] NMI watchdog: BUG: soft lockup - CPU#1 stuck for 23s!
> [swapper/1:0]
> [  216.060945] Modules linked in: hello_2(O) Bla Bla Bla...
>
>
> /*
>  *  hello-2.c - Demonstrating the module_init() and module_exit() macros.
>  *  This is preferred over using init_module() and cleanup_module().
>  */
> #include <linux/module.h>       /* Needed by all modules */
> #include <linux/kernel.h>       /* Needed for KERN_INFO */
> #include <linux/init.h>         /* Needed for the macros */
> #include <linux/timer.h>
>
> MODULE_LICENSE("GPL");
>
> static struct timer_list my_timer;
>
> void my_timer_callback( unsigned long data )
> {
>   int delay = 0;
>   int delay2;
>   int delay3;
>   int delay4;
>   volatile int glob_test;
>
>   glob_test = 1000000;
>
>
>   printk( "my_timer_callback called (%ld).\n", jiffies );
>   for ( delay4 = 0; delay4 < 99; delay4 += 1)
>   {
>   for ( delay3 = 0; delay3 < 99; delay3 += 1)
>   {
>      for ( delay2 = 0; delay2 < 99; delay2 += 1)
>      {
>         //printk( "my_timer_callback loop %d.\n",delay2);
>         for( delay = 0; delay < 99; delay += 1)
>         {
>            if (delay > glob_test) { printk("What??\n");}
>         }
>      }
>   }
>   }
>  printk( "my_timer_callback done.\n" );
> }
>
>
> static int __init hello_2_init(void)
> {
>   int ret;
>   printk("Timer module installing\n");
>
>   // my_timer.function, my_timer.data
>   setup_timer( &my_timer, my_timer_callback, 0 );
>
>   printk( "Starting timer to fire in 200ms (%ld)\n", jiffies );
>   ret = mod_timer( &my_timer, jiffies + msecs_to_jiffies(200) );
>   if (ret) printk("Error in mod_timer\n");
>         return 0;
> }
>
> static void __exit hello_2_exit(void)
> {
> //      printk(KERN_INFO "Goodbye, world 2\n");
>   int ret;
>   ret = del_timer( &my_timer );
>   if (ret) printk("The timer is still in use...\n");
>
>   printk("Timer module uninstalling\n");
>
> }
>
> module_init(hello_2_init);
> module_exit(hello_2_exit);
>
>
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>

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