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SubjectRe: [patch] Race between init_idle and reschedule_idle
* Martin J. Bligh <Martin.Bligh@us.ibm.com> [20010930 01;50]:"
> On an SMP system, if the boot cpu calls reschedule_idle before the
> secondary cpus have all called init_idle, we hit the following code
> in reschedule_idle:
>
> ...
> for (i = 0; i < smp_num_cpus; i++) {
> cpu = cpu_logical_map(i);
> if (!can_schedule(p, cpu))
> continue;
> tsk = cpu_curr(cpu);
> ...
>
> Because init_idle hasn't run for all cpus yet, the expression
> "cpu_curr(cpu)"
> gives us NULL. When we derefernce an offset of 0x50 off tsk a few
> nanoseconds later we panic, complaining vaddr 0x00000050 is invalid.
>
> This is more likely to happen on larger systems, but could happen on any
> SMP system (especially if I enable serial console, which really slows down
> the secondary procs doing printk ;-) ). If you want to see the panic /
> analysis,
> I can send it.
>
> Thanks to Alan Cox & Andrew Morton for showing me how to serialise the
> cpus to make the panic legible. The following patch holds back the boot
> cpu at the end of smp_init until all the secondarys have done init_idle:
>

martin, we experienced the same problem way back when we brought our
Fujitsu based Numa machine up. We also experience the problem with
our cpu pooling and load balancing approach. I think the ksoftirq might
have similar problems.
We solved it in a similar fashion, through counters.
I strongly suggest to put this code into the main track.

-- Hubertus

> --- virgin-2.4.10/kernel/sched.c Mon Sep 17 23:03:09 2001
> +++ linux-2.4.10/kernel/sched.c Sat Sep 29 19:57:10 2001
> @@ -1309,6 +1309,8 @@
> atomic_inc(&current->files->count);
> }
>
> +extern volatile unsigned long wait_init_idle;
> +
> void __init init_idle(void)
> {
> struct schedule_data * sched_data;
> @@ -1321,6 +1323,7 @@
> }
> sched_data->curr = current;
> sched_data->last_schedule = get_cycles();
> + clear_bit(current->processor, &wait_init_idle);
> }
>
> extern void init_timervecs (void);
> --- virgin-2.4.10/init/main.c Thu Sep 20 21:02:01 2001
> +++ linux-2.4.10/init/main.c Sat Sep 29 21:11:52 2001
> @@ -477,6 +477,8 @@
> extern void setup_arch(char **);
> extern void cpu_idle(void);
>
> +volatile unsigned long wait_init_idle = 0UL;
> +
> #ifndef CONFIG_SMP
>
> #ifdef CONFIG_X86_IO_APIC
> @@ -490,13 +492,25 @@
>
> #else
>
> +
> /* Called by boot processor to activate the rest. */
> static void __init smp_init(void)
> {
> /* Get other processors into their bootup holding patterns. */
> smp_boot_cpus();
> + wait_init_idle = cpu_online_map;
> + clear_bit(current->processor, &wait_init_idle); /* Don't wait on me! */
> + printk("Waiting on wait_init_idle (map = 0x%lx)\n", wait_init_idle);
> smp_threads_ready=1;
> smp_commence();
> +
> + /* Wait for the other cpus to set up their idle processes */
> + while (1) {
> + if (!wait_init_idle)
> + break;
> + rep_nop();
> + }
> + printk("All processors have done init_idle\n");
> }
>
> #endif
>
>
>
> -
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