Re: cgroup_fj tests will stick the nort kernel

[Li Zefan <lizefan@huawei.com>]

On 2013/4/19 15:30, Qiang Huang wrote:
> Hi,
> 
> I ran cgroup_fj tests on RT kernel with PREEMPT_RT_FULL disabled, it will
> stick the system when ran cpuset stress tests, it happens everytime.
> 
> Here stick the system means there are almost no response from the system and
> we can hardly do anything on the terminal, but kernel isn't crash nor deadlocked
> (according to the lockdep message), and it may do some response sometimes.
> 
> The problem exists on all RT versions from 3.4.18-rt29 to 3.4.37-rt51 AFAIK, but
> without RT patches or with PREEMPT_RT_FULL enabled, the problem isn't exists.
> 
> When the system is stuck, we will get the following message:
> # dmesg
> ...

I've found the culprit after some investigation:

From: Thomas Gleixner <tglx@linutronix.de>
Date: Fri, 04 Nov 2011 19:48:36 +0000
Subject: sched-clear-pf-thread-bound-on-fallback-rq.patch

At system boot when some cpus haven't been up, the scheduler calls select_fallback_rq()
and schedules tasks in other cpus, which ends up clearing some kernel threads'
PF_THREAD_BOUND flag...