Re: [LTP] [PATCH] controllers: disallow attaching kthreadd or PF_THREAD_BOUND threads to cgroups on kernel > 3.4.0

[Wanlong Gao <gaowanlong@cn.fujitsu.com>]

On 01/19/2015 04:36 PM, Li Jinyue wrote:
> For kernel commit c4c27fbdda4e8ba87806c415b6d15266b07bce4b,
> disallow attaching kthreadd or PF_THREAD_BOUND threads to cgroups.
> 
> So, we kindly avoid to attach these threads in cgroup tests.
> 
> Signed-off-by: Li Jinyue <lijinyue@huawei.com>
> ---
>  testcases/kernel/controllers/cgroup_fj/cgroup_fj_function.sh | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/testcases/kernel/controllers/cgroup_fj/cgroup_fj_function.sh b/testcases/kernel/controllers/cgroup_fj/cgroup_fj_function.sh
> index 30476bd..30fffb6 100755
> --- a/testcases/kernel/controllers/cgroup_fj/cgroup_fj_function.sh
> +++ b/testcases/kernel/controllers/cgroup_fj/cgroup_fj_function.sh
> @@ -186,6 +186,16 @@ case $attach_operation in
>  	do
>  		cur_pid=`sed -n "$i""p" $TMPFILE`
>  		if [ -e /proc/$cur_pid/ ];then
> +			#For kernel 3.4.0 and higher,kernel disallow attaching kthreadd or
> +			#PF_THREAD_BOUND threads to cgroups.

I check the current kernel and find that this flag already removed now, please check the following
commit:

commit 14a40ffccd6163bbcd1d6f32b28a88ffe6149fc6
Author: Tejun Heo <tj@kernel.org>
Date:   Tue Mar 19 13:45:20 2013 -0700

    sched: replace PF_THREAD_BOUND with PF_NO_SETAFFINITY
    
    PF_THREAD_BOUND was originally used to mark kernel threads which were
    bound to a specific CPU using kthread_bind() and a task with the flag
    set allows cpus_allowed modifications only to itself.  Workqueue is
    currently abusing it to prevent userland from meddling with
    cpus_allowed of workqueue workers.


> +			#kernel commit: c4c27fbdda4e8ba87806c415b6d15266b07bce4b
> +			tst_kvercmp 3 4 0
> +			if [ $? -ne 0 ]; then

And where to go if tst_kvercmp failed and return -1?

> +				thread_flag=`cat /proc/$cur_pid/stat | awk '{print $9}'`
> +				if [ $cur_pid -eq 2 -o $((${thread_flag}&0x04000000)) -eq 67108864 ];then

These magic numbers must at least be commented to be understand easily.

Thanks,
Wanlong Gao

> +					continue
> +				fi
> +			fi
>  			do_echo 1 1 "$cur_pid" /dev/cgroup/subgroup_1/tasks
>  		fi
>  	done
> 


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