At 10/09/2012 02:21 PM, David Rientjes Wrote:
> On Mon, 8 Oct 2012, Tang Chen wrote:
>
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index 66b36ab..e76dce9 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -1263,18 +1263,24 @@ EXPORT_SYMBOL_GPL(kick_process);
>> */
>> static int select_fallback_rq(int cpu, struct task_struct *p)
>> {
>> - const struct cpumask *nodemask = cpumask_of_node(cpu_to_node(cpu));
>> + int nid = cpu_to_node(cpu);
>> + const struct cpumask *nodemask = NULL;
>> enum { cpuset, possible, fail } state = cpuset;
>> int dest_cpu;
>>
>> - /* Look for allowed, online CPU in same node. */
>> - for_each_cpu(dest_cpu, nodemask) {
>> - if (!cpu_online(dest_cpu))
>> - continue;
>> - if (!cpu_active(dest_cpu))
>> - continue;
>> - if (cpumask_test_cpu(dest_cpu, tsk_cpus_allowed(p)))
>> - return dest_cpu;
>> + /* If the cpu has been offlined, its nid was set to -1. */
>> + if (nid != -1) {
>
> NUMA_NO_NODE.
>
> Eek, the nid shouldn't be -1 yet, though, for cpu hotplug since this
> should be called at CPU_DYING level and migrate_tasks() still sees a valid
> cpu.
the cpu's node is set when the cpu is hotpluged(not online), and it will
be cleared when the cpu is hotremoved(This patch is in akpm tree):
https://lkml.org/lkml/2012/9/3/39
I guess the task is in sleep state when the cpu is offlined, and it doesn't
be migrated to another cpu.
Thanks
Wen Congyang
>
> On x86, cpumask_of_node() is always guaranteed to return a valid cpumask
> after boot so presumably this is a problem in some non-x86 arch code and
> isn't actually a sched problem.
>
>> + nodemask = cpumask_of_node(nid);
>> +
>> + /* Look for allowed, online CPU in same node. */
>> + for_each_cpu(dest_cpu, nodemask) {
>> + if (!cpu_online(dest_cpu))
>> + continue;
>> + if (!cpu_active(dest_cpu))
>> + continue;
>> + if (cpumask_test_cpu(dest_cpu, tsk_cpus_allowed(p)))
>> + return dest_cpu;
>> + }
>> }
>>
>> for (;;) {
>
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