linux-kernel - Re: [BUG: NULL pointer dereference] cgroups and RT scheduling interact badly.

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Message-Id: <1213612447.16944.99.camel@twins>
Date:	Mon, 16 Jun 2008 12:34:07 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Daniel K." <dk@...no>
Cc:	mingo@...e.hu, menage@...gle.com,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [BUG: NULL pointer dereference] cgroups and RT scheduling
	interact badly.

On Sun, 2008-06-15 at 00:26 +0200, Daniel K. wrote:
> I get the following on the latest Linus git tree.
> 
> Testcase:
> 
> mkdir /dev/cgroup
> mount -t cgroup -o cpu,cpuset cgroup /dev/cgroup
> 
> mkdir -p /dev/cgroup/burn/oops
> cd /dev/cgroup/burn
> 
> echo 3 > cpuset.cpus
> echo 0 > cpuset.mems
> echo 1000000 > cpu.rt_period_us
> echo 940000  > cpu.rt_runtime_us
> 
> echo 3 > oops/cpuset.cpus
> echo 0 > oops/cpuset.mems
> echo 100000 > oops/cpu.rt_period_us
> echo 4000 > oops/cpu.rt_runtime_us
> 
> echo $$ > oops/tasks
> schedtool -R -p 1 -e burnP6
> 
> And then it breaks into the pieces below, as captured by netconsole.

Excellent report, thanks!


Does the below work for you?


Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
---
Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c
+++ linux-2.6/kernel/sched.c
@@ -7784,7 +7784,6 @@ static void init_tg_rt_entry(struct task
 	else
 		rt_se->rt_rq = parent->my_q;
 
-	rt_se->rt_rq = &rq->rt;
 	rt_se->my_q = rt_rq;
 	rt_se->parent = parent;
 	INIT_LIST_HEAD(&rt_se->run_list);

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