Re: modular net drivers

[Philipp Rumpf <prumpf@xxxxxxxxxxxxxxxxxxxxxx>]

On Sun, Jun 25, 2000 at 01:30:50AM +1000, Andrew Morton wrote:
> +static volatile int ice_block;
> +static spinlock_t freeze_lock = SPIN_LOCK_UNLOCKED;
> +
> +static int
> +antarctica(void *dummy)
> +{
> +     printk("start antarctica on %d\n", smp_processor_id());
> +     while (ice_block)
> +             ;
> +     printk("stop antarctica on %d\n", smp_processor_id());
> +     return 0;
> +}
> +
> +static int
> +freeze_other_cpus(void)
> +{
> +     int cpu, retval;
> +
> +     if (!spin_trylock(&freeze_lock))
> +             return -EAGAIN;
> +
> +     printk("start freeze_other_cpus()\n");
> +     ice_block = 1;
> +     for (cpu = 0; cpu < smp_num_cpus - 1; cpu++) {
> +             retval = kernel_thread(antarctica, (void *)0, 0);
> +             if (retval < 0)
> +                     goto out_melt;
> +     }
> +     printk("continue freeze_other_cpus()\n");
> +     return 0;
> +out_melt:
> +     ice_block = 0;
> +     spin_unlock(&freeze_lock);
> +     return retval;
> +}

You don't guarantee all the other kernel_threads have started executing.

Basically you need either an atomic_inc or a per-CPU flag somewhere.

        Philipp Rumpf