Re: failing kthread_create_on_node()

[Konrad Eisele <konrad@xxxxxxxxxxx>]

David Miller wrote:
> From: Konrad Eisele<konrad@xxxxxxxxxxx>
> Date: Tue, 17 Apr 2012 08:37:50 +0200
>
> > 2. What happens next
> >
> >     CPU1 will boot up and execute schedule().
> >     ...
> >     ->  kernel/core.c:__schedule()
>
> The stop thread doesn't actually run immediately when it is created,
> so will need to be woken up to be scheduled and run.
>
> At wakeup time, set_task_cpu() should fix things up and make the
> task have a correct ->cpu in it's thread_info.
>
> I wonder if one of the sparc32 global cpu masks isn't being
> initialized properly.
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I have posted
"[PATCH 1/1] sparc: task_cpu() for stopper thread on sparc32 returns 0"

I traced it further and you where right, the stop thread of CPU1 was
sleeping.
The reason that the stopper thread for cpu-1 gets inserted into runqueue-0
(which causes fatal failure later on) is traced below:

When CPU1 comes online it is woken up. Then I end up in
the following call path:

-> kernel/sched/core.c():try_to_wake_up():
        ...
1628:	cpu = select_task_rq(p, SD_BALANCE_WAKE, wake_flags);
1629:	if (task_cpu(p) != cpu) {
        ...
     -> kernel/sched/core.c:select_task_rq():
          ...
1332:	  int cpu = p->sched_class->select_task_rq(p, sd_flags, wake_flags);
          ...
        -> kernel/sched/stop_task.c:select_task_rq_stop():
            ...
16:         return task_cpu(p); /* stop tasks as never migrate */
            ...


however task_cpu(p) is 0.

The patch posted checks weather a different cpu should be returned in
kernel/sched/stop_task.c:select_task_rq_stop().

Hope that makes sense.

-- Konrad





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