Re: [PATCH] cgroups: move cpuset specific checks from generic code to cpuset_can_attach (v2)

[Mike Galbraith <umgwanakikbuti@gmail.com>]

On Thu, 2015-11-26 at 20:32 -0200, Marcelo Tosatti wrote:
> Move PF_NO_SETAFFINITY and kthreadd_task checks to cpuset cgroups,  
> where they belong. This makes it possible to attach PF_NO_SETAFFINITY 
> tasks to Intel CAT cgroup.
> 
> Reported-by: Luiz Capitulino <lcapitulino@redhat.com>
> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
> Reviewed-by: Chao Peng <chao.p.peng@linux.intel.com>
> 
> v2: "PF_NO_SETAFFINITY check" -> "PF_NO_SETAFFINITY and kthreadd_task
> checks"
> 
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index f89d929..0603652 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -2466,16 +2466,6 @@ static ssize_t __cgroup_procs_write(struct kernfs_open_file *of, char *buf,
>  	if (threadgroup)
>  		tsk = tsk->group_leader;
>  
> -	/*
> -	 * Workqueue threads may acquire PF_NO_SETAFFINITY and become
> -	 * trapped in a cpuset, or RT worker may be born in a cgroup
> -	 * with no rt_runtime allocated.  Just say no.
> -	 */
> -	if (tsk == kthreadd_task || (tsk->flags & PF_NO_SETAFFINITY)) {
> -		ret = -EINVAL;
> -		goto out_unlock_rcu;
> -	}
> -
>  	get_task_struct(tsk);
>  	rcu_read_unlock();
>  
> diff --git a/kernel/cpuset.c b/kernel/cpuset.c
> index f0acff0..9fff4d6 100644
> --- a/kernel/cpuset.c
> +++ b/kernel/cpuset.c
> @@ -53,6 +53,7 @@
>  #include <linux/time.h>
>  #include <linux/backing-dev.h>
>  #include <linux/sort.h>
> +#include <linux/kthread.h>
>  
>  #include <asm/uaccess.h>
>  #include <linux/atomic.h>
> @@ -1445,6 +1446,17 @@ static int cpuset_can_attach(struct cgroup_subsys_state *css,
>  		goto out_unlock;
>  
>  	cgroup_taskset_for_each(task, tset) {
> +		/*
> +		 * Workqueue threads may acquire PF_NO_SETAFFINITY and become
> +		 * trapped in a cpuset, or RT worker may be born in a cgroup
> +		 * with no rt_runtime allocated.  Just say no.
> +		 */
> +		if (task == kthreadd_task ||
> +		    (task->flags & PF_NO_SETAFFINITY)) {
> +			ret = -EINVAL;
> +			goto out_unlock;
> +		}
> +
>  		ret = task_can_attach(task, cs->cpus_allowed);
>  		if (ret)
>  			goto out_unlock;

Note the rt_runtime reference in the comment, that wasn't about cpuset.
The kthreadd wants to remain immune to all fiddlings methinks.

	-Mike