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SubjectRe: [v3.10-rc1] WARNING: at kernel/rcutree.c:502
Date
"Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com> writes:
> On 05/13/2013 08:09 PM, Bjørn Mork wrote:
>
>> Hey, hey, hey. Turns out this wasn't that wrong after all. That merge
>> includes a oneline diff in kernel/cpu/idle.c and it *is* actually this
>> diff which trigger the problem for me. Reverting it, using the attached
>> patch, makes the warning go away. Which means that it had nothing to do
>> with your RCU changes.
>>
>> But I haven't the faintest idea how this is supposed to work, or even
>> how to explain the patch properly, so I think I need some help from
>> Thomas here. Unless this makes you understand the real issue?
>>
>> Thomas, why does powertop trigger the
>>
>> WARNING: at kernel/rcutree.c:502 rcu_eqs_exit_common.isra.48+0x3d/0x125()
>>
>> without the attached patch? And what is the proper resolution?
>>
>
> The problem appears to be in the cpu idle poll implementation. You can trigger
> this problem by passing idle=poll in the kernel cmd-line as well, right?

That sounded so obvious that it made me think "Doh, why didn't I just
test that before?" But unfortunately there must be some other factor
involved. No warnings observed during normal use when running with
idle=poll:

bjorn@nemi:~$ dmesg|grep polling
[ 0.000000] process: using polling idle threads


I expected a flood of warnings here, but there is none until I start
powertop (to confirm that the original issue is still there). So it's
more than just entering cpu_idle_poll().

> I think I understand what is going on here. Can you please try the fix below?
> (It is only compile-tested since its very late here and I really need to get
> some sleep!).

Works perfect. Thanks. I assume this is the correct fix even if the
problem isn't completely understood?



Bjørn
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