Re: [gentoo-user] unstoppable, undeciperable kernel call trace in log

[Maxim Wexler]

This is weird

syzygy@lumby ~ $ grep DEBUG_FS /usr/src/linux/.config
# CONFIG_DEBUG_FS is not set

But the entry in menuconfig ->kernel hacking looks like this:' -*-
Debug Filesystem', and can't be changed.  Not '[*]' which is
changeable with the spacebar, but '-*-' which is not.

According to <help> it depends on TREE_RCU_TRACE=y OR <a whole bunch
of other stuff>.

But I have TREE_RCU_TRACE=y. So I should be good right? But then why
doesn't it select DEBUG_FS?

googling lead me to http://en.wikipedia.org/wiki/Debugfs,  which says
do: 'mount -t debugfs none /sys/kernel/debug'. Ok, but there's no
debug file or dir under /sys/kernel. Do I make one? And will it make a
difference since according to grep DEBUG_FS is not set in the kernel
config?

I'll go and make the new kernel and see what happens.


On 6/30/12, Maxim Wexler <maxim.wexler@×××××.com> wrote:
>> Hi,
>>
>> I don't have an answer, but if you google the phrase "rcu_bh detected
>> stall on CPU" you can find many reports similar to yours and maybe
>> some information.
>
> This might be usefu
> lhttp://www.kernel.org/doc/Documentation/RCU/stallwarn.txt
>
> "RCU bugs can often be debugged with the help of CONFIG_RCU_TRACE"
>
> from <help> in menuconfig.
>
>   │ This option provides tracing in RCU which presents stats
> │
>   │ in debugfs for debugging RCU implementation.
>
> Ok, so I've  set the RCU_TRACE=y. Next question: How do I use debugfs,
> never used it before?
>
>>
>> Do you have RCU_CPU_STALL_INFO=y in your kernel config?
>
> no.
>
> syzygy@lumby ~ $ grep RCU /usr/src/linux/.config
> # RCU Subsystem
> CONFIG_TREE_RCU=y
> # CONFIG_PREEMPT_RCU is not set
> # CONFIG_RCU_TRACE is not set
> CONFIG_RCU_FANOUT=32
> # CONFIG_RCU_FANOUT_EXACT is not set
> # CONFIG_RCU_FAST_NO_HZ is not set
> # CONFIG_TREE_RCU_TRACE is not set
> # CONFIG_SPARSE_RCU_POINTER is not set
> CONFIG_RCU_CPU_STALL_TIMEOUT=60
>