Re: kernel BUG at kernel/sched_rt.c:493!

From: Shawn Bohrer
Date: Mon Jan 07 2013 - 12:58:14 EST

On Sat, Jan 05, 2013 at 11:46:32AM -0600, Shawn Bohrer wrote:
> I've tried reproducing the issue, but so far I've been unsuccessful
> but I believe that is because my RT tasks aren't using enough CPU
> cause borrowing from the other runqueues. Normally our RT tasks use
> very little CPU so I'm not entirely sure what conditions caused them
> to run into throttling on the day that this happened.

I've managed to reproduce this a couple times now on 3.1.9 I'll give
this a try later with a more recent kernel. Here is what I've done to
reproduce the issue.

# Setup in shell 1
root@berbox39:/cgroup/cpuset# mkdir package0
root@berbox39:/cgroup/cpuset# echo 0 > package0/cpuset.mems
root@berbox39:/cgroup/cpuset# echo 0,2,4,6 > package0/cpuset.cpus
root@berbox39:/cgroup/cpuset# cat cpuset.sched_load_balance
root@berbox39:/cgroup/cpuset# cat package0/cpuset.sched_load_balance
root@berbox39:/cgroup/cpuset# cat sysdefault/cpuset.sched_load_balance
root@berbox39:/cgroup/cpuset# echo 1,3,5,7 > sysdefault/cpuset.cpus
root@berbox39:/cgroup/cpuset# echo 0 > sysdefault/cpuset.mems
root@berbox39:/cgroup/cpuset# echo $$ > package0/tasks

# Setup in shell 2
root@berbox39:~# cd /cgroup/cpuset/
root@berbox39:/cgroup/cpuset# chrt -f -p 60 $$
root@berbox39:/cgroup/cpuset# echo $$ > sysdefault/tasks

# In shell 1
root@berbox39:/cgroup/cpuset# chrt -f 1 /root/ &
root@berbox39:/cgroup/cpuset# chrt -f 1 /root/ &

# In shell 2
root@berbox39:/cgroup/cpuset# echo 0 > cpuset.sched_load_balance
root@berbox39:/cgroup/cpuset# echo 1 > cpuset.sched_load_balance
root@berbox39:/cgroup/cpuset# echo 0 > cpuset.sched_load_balance
root@berbox39:/cgroup/cpuset# echo 1 > cpuset.sched_load_balance

I haven't found the exact magic combination but I've been going back
and forth adding/killing processes and toggling
cpuset.sched_load_balance and in a couple of minutes I can usually get
the machine to trigger the bug.



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