Sachin found cpu hotplug test failures on powerpc, which made the kernel hang on his POWER box. The problem is that we fail to re-activate a cpu when a hot-unplug fails. Fix this by moving the de-activation into _cpu_down after doing the initial checks. Remove the synchronize_sched() calls and rely on those implied by rebuilding the sched domains using the new mask. Reported-by: Sachin Sant Signed-off-by: Xiaotian Feng Tested-by: Sachin Sant Signed-off-by: Peter Zijlstra --- kernel/cpu.c | 24 +++--------------------- 1 file changed, 3 insertions(+), 21 deletions(-) Index: linux-2.6/kernel/cpu.c =================================================================== --- linux-2.6.orig/kernel/cpu.c +++ linux-2.6/kernel/cpu.c @@ -209,6 +209,7 @@ static int __ref _cpu_down(unsigned int return -ENOMEM; cpu_hotplug_begin(); + set_cpu_active(cpu, false); err = __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE | mod, hcpu, -1, &nr_calls); if (err == NOTIFY_BAD) { @@ -280,18 +281,6 @@ int __ref cpu_down(unsigned int cpu) goto out; } - set_cpu_active(cpu, false); - - /* - * Make sure the all cpus did the reschedule and are not - * using stale version of the cpu_active_mask. - * This is not strictly necessary becuase stop_machine() - * that we run down the line already provides the required - * synchronization. But it's really a side effect and we do not - * want to depend on the innards of the stop_machine here. - */ - synchronize_sched(); - err = _cpu_down(cpu, 0); out: @@ -382,19 +371,12 @@ int disable_nonboot_cpus(void) return error; cpu_maps_update_begin(); first_cpu = cpumask_first(cpu_online_mask); - /* We take down all of the non-boot CPUs in one shot to avoid races + /* + * We take down all of the non-boot CPUs in one shot to avoid races * with the userspace trying to use the CPU hotplug at the same time */ cpumask_clear(frozen_cpus); - for_each_online_cpu(cpu) { - if (cpu == first_cpu) - continue; - set_cpu_active(cpu, false); - } - - synchronize_sched(); - printk("Disabling non-boot CPUs ...\n"); for_each_online_cpu(cpu) { if (cpu == first_cpu) -- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/