10.11.2014, 19:45, "Sasha Levin" <[email protected]>:
> On 11/10/2014 11:36 AM, Kirill Tkhai wrote:
>> I mean task_numa_find_cpu(). If a garbage is in
>> cpumask_of_node(env->dst_nid)
>> and cpu is bigger than mask, the check
>>
>> cpumask_test_cpu(cpu, tsk_cpus_allowed(env->p)
>>
>> may be true.
>>
>> So, we dereference wrong rq in task_numa_compare(). It's not rq at all.
>> Strange cpu may be from here. It's just a int number in a wrong memory.
>
> But the odds of the spinlock magic and owner pointer matching up are slim
> to none in that case. The memory is also likely to be valid since KASAN didn't
> complain about the access, so I don't believe it to be an access to freed
> memory.
I'm not good with lockdep checks, so I can't judge right now...
Just a hypothesis.
>> A hypothesis that below may help:
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 826fdf3..a2b4a8a 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -1376,6 +1376,9 @@ static void task_numa_find_cpu(struct task_numa_env
>> *env,
>> {
>> int cpu;
>>
>> + if (!node_online(env->dst_nid))
>> + return;
>
> I've changed that to BUG_ON(!node_online(env->dst_nid)) and will run it for a
> bit.
I've looked one more time, and it looks like it's better to check for
BUG_ON(env->dst_nid > MAX_NUMNODES). node_online() may do not work for
insane nids.
Anyway, even if it's not connected, we need to initialize numa_preferred_nid
of init_task, because it's inherited by kernel_init() (and /sbin/init too).
I'll send the patch tomorrow.
Kirill
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