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Subject: Re: [gentoo-user] unstoppable, undeciperable kernel call trace in log
From: Maxim Wexler <maxim.wexler@gmail.com>
To: gentoo-user@lists.gentoo.org
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> 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.

  =E2=94=82 This option provides tracing in RCU which presents stats       =
         =E2=94=82
  =E2=94=82 in debugfs for debugging RCU implementation.

Ok, so I've  set the RCU_TRACE=3Dy. Next question: How do I use debugfs,
never used it before?

>
> Do you have RCU_CPU_STALL_INFO=3Dy in your kernel config?

no.

syzygy@lumby ~ $ grep RCU /usr/src/linux/.config
# RCU Subsystem
CONFIG_TREE_RCU=3Dy
# CONFIG_PREEMPT_RCU is not set
# CONFIG_RCU_TRACE is not set
CONFIG_RCU_FANOUT=3D32
# 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=3D60