(bisected) Lock up on sh73a0/kzm9g on cpuidle initialization

[Geert Uytterhoeven]

On Fri, Nov 7, 2014 at 8:59 AM, Geert Uytterhoeven <geert at linux-m68k.org> wrote:
> On Thu, Nov 6, 2014 at 10:02 PM, Daniel Lezcano
> <daniel.lezcano at linaro.org> wrote:
>> On 11/06/2014 09:38 PM, Geert Uytterhoeven wrote:
>>> When CONFIG_CPU_IDLE=y, the kernel locks up during cpuidle initialization
>>> on Renesas sh73a0/kzm9g-reference, which has a dual-core Cortex-A9.
>>>
>>> Last message is:
>>>
>>>      DMA: preallocated 256 KiB pool for atomic coherent allocations
>>>
>>> After this it's supposed to print:
>>>
>>>      cpuidle: using governor ladder
>>>      cpuidle: using governor menu
>>>
>>> I've bisected this to commit 442bf3aaf55a91ebfec71da46a4ee10a3c905bcc
>>> ("sched: Let the scheduler see CPU idle states").
>>>
>>> Reverting that commit, and commit 83a0a96a5f26d974580fd7251043ff70c8f1823d
>>> ("sched/fair: Leverage the idle state info when choosing the "idlest"
>>> cpu") which
>>> depends on it, fixes the problem.
>>>
>>> I saw the discussion "lockdep splat in CPU hotplug", so I enabled lockdep
>>> debugging, but didn't see a lockdep splat.
>>
>> Did you try the fix attached ?
>>
>> https://lkml.org/lkml/2014/10/22/722
>
> Thanks, I didn't try that.
>
> However, this patch seems to be in v3.18-rc3, so I'm already using it.
> Hence it doesn't fix the problem for me.
>
> On another board, with a dual Cortex-A15, the problem doesn't show up.

This problem (regression introduced in v3.18-rc1) is still present in v3.18-rc6.

I did some more investigations, and it's hanging in the call to
synchronize_rcu() in cpuidle_uninstall_idle_handler(), which was added in
commit 442bf3aaf55a91ebfec71da46a4ee10a3c905bcc.
More specificailly, it's blocked on the wait_for_completion(&rcu.completion)
in kernel/rcu/update.c:void wait_rcu_gp(call_rcu_func_t crf).

Anyone with a clue?

Thanks again!

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds