From 6ad4c18884e864cf4c77f9074d3d1816063f99cd Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Wed, 25 Nov 2009 13:31:39 +0100 Subject: sched: Fix balance vs hotplug race Since (e761b77: cpu hotplug, sched: Introduce cpu_active_map and redo sched domain managment) we have cpu_active_mask which is suppose to rule scheduler migration and load-balancing, except it never (fully) did. The particular problem being solved here is a crash in try_to_wake_up() where select_task_rq() ends up selecting an offline cpu because select_task_rq_fair() trusts the sched_domain tree to reflect the current state of affairs, similarly select_task_rq_rt() trusts the root_domain. However, the sched_domains are updated from CPU_DEAD, which is after the cpu is taken offline and after stop_machine is done. Therefore it can race perfectly well with code assuming the domains are right. Cure this by building the domains from cpu_active_mask on CPU_DOWN_PREPARE. Signed-off-by: Peter Zijlstra LKML-Reference: Signed-off-by: Ingo Molnar --- kernel/cpu.c | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-) (limited to 'kernel/cpu.c') diff --git a/kernel/cpu.c b/kernel/cpu.c index 6ba0f1ecb21..b2168864037 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -212,6 +212,8 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen) err = __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE | mod, hcpu, -1, &nr_calls); if (err == NOTIFY_BAD) { + set_cpu_active(cpu, true); + nr_calls--; __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod, hcpu, nr_calls, NULL); @@ -223,11 +225,11 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen) /* Ensure that we are not runnable on dying cpu */ cpumask_copy(old_allowed, ¤t->cpus_allowed); - set_cpus_allowed_ptr(current, - cpumask_of(cpumask_any_but(cpu_online_mask, cpu))); + set_cpus_allowed_ptr(current, cpu_active_mask); err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu)); if (err) { + set_cpu_active(cpu, true); /* CPU didn't die: tell everyone. Can't complain. */ if (raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod, hcpu) == NOTIFY_BAD) @@ -292,9 +294,6 @@ int __ref cpu_down(unsigned int cpu) err = _cpu_down(cpu, 0); - if (cpu_online(cpu)) - set_cpu_active(cpu, true); - out: cpu_maps_update_done(); stop_machine_destroy(); @@ -387,6 +386,15 @@ int disable_nonboot_cpus(void) * 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) -- cgit v1.2.3