Re: [PATCH 1/7] work_on_cpu: helper for doing task on a CPU.

From: Rusty Russell
Date: Thu Oct 23 2008 - 23:04:45 EST

On Friday 24 October 2008 01:36:05 Gautham R Shenoy wrote:
> OK, how about doing the following? That will solve the problem
> of deadlock you pointed out in patch 6.
> get_online_cpus();
> if (likely(per_cpu(cpu_state, cpuid) == CPU_ONLINE)) {
> schedule_work_on(cpu, &;
> flush_work(&;
> } else if (per_cpu(cpu_state, cpuid) != CPU_DEAD)) {
> /*
> * We're the CPU-Hotplug thread. Call the
> * function synchronously so that we don't
> * deadlock with any pending work-item blocked
> * on get_online_cpus()
> */
> cpumask_t orignal_mask = current->cpus_allowed;
> set_cpus_allowed_ptr(current, &cpumask_of_cpu(cpu);
> wfc.ret = fn(arg);
> set_cpus_allowed_ptr(current, &original_mask);
> }

Hi Gautham, Oleg,

Unfortunately that's exactly what I'm trying to get away from: another cpumask
on the stack :(

The cpu hotplug thread is just whoever wrote 0 to "online" in sys. And in
fact it already plays with its cpumask, which should be fixed too.

I think we should BUG_ON(per_cpu(cpu_state, cpuid) != CPU_DEAD) to ensure we
never use work_on_cpu in the hotplug cpu path. Then we use
smp_call_function() for that hard intel_cacheinfo case. Finally, we fix the
cpu hotplug path to use schedule_work_on() itself rather than playing games
with cpumask.

If you agree, I'll spin the patches...

Thanks for the brainpower,
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at