[Devel] Re: [PATCH] cgroups: respect cgroup timer slack value in prctl

[Matt Helsley]

On Tue, Feb 01, 2011 at 02:41:43PM -0800, jacob.jun.pan at linux.intel.com wrote:
> From: Jacob Pan <jacob.jun.pan at linux.intel.com>
> 
> Per cgroup timer slack value is used to manage task groups
> for more friendly power management behavior. Once a task is
> attached to a cgroup, we should not allow user to change
> (escape) the per cgroup restriction unless a more relaxed
> timer slack value is given by user via prctl.
> 
> Signed-off-by: Jacob Pan <jacob.jun.pan at linux.intel.com>

> ---
>  include/linux/cgroup.h      |   13 +++++++++++++

Looks like the original two patches (one or more implementing:

>  kernel/cgroup_timer_slack.c |    4 ----

) were not sent to containers at lists.linux-foundation.org ?

>  kernel/sys.c                |   21 ++++++++++++++++++++-
>  3 files changed, 33 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
> index ed4ba11..4405666 100644
> --- a/include/linux/cgroup.h
> +++ b/include/linux/cgroup.h
> @@ -627,6 +627,19 @@ bool css_is_ancestor(struct cgroup_subsys_state *cg,
>  unsigned short css_id(struct cgroup_subsys_state *css);
>  unsigned short css_depth(struct cgroup_subsys_state *css);
> 
> +#ifdef CONFIG_CGROUP_TIMER_SLACK
> +struct timer_slack_cgroup {
> +	struct cgroup_subsys_state css;
> +	unsigned long timer_slack_ns;
> +};
> +
> +static inline struct timer_slack_cgroup *task_timer_slack(struct task_struct *task)
> +{
> +	return container_of(task_subsys_state(task, timer_slack_subsys_id),
> +			    struct timer_slack_cgroup, css);
> +}
> +#endif
> +
>  #else /* !CONFIG_CGROUPS */
> 
>  static inline int cgroup_init_early(void) { return 0; }
> diff --git a/kernel/cgroup_timer_slack.c b/kernel/cgroup_timer_slack.c
> index daa452d..1de122a 100644
> --- a/kernel/cgroup_timer_slack.c
> +++ b/kernel/cgroup_timer_slack.c
> @@ -4,10 +4,6 @@
>  #include <linux/slab.h>
> 
>  struct cgroup_subsys timer_slack_subsys;
> -struct timer_slack_cgroup {
> -	struct cgroup_subsys_state css;
> -	unsigned long timer_slack_ns;
> -};
> 
>  static struct timer_slack_cgroup *cgroup_to_tslack_cgroup(struct cgroup *cgroup)
>  {
> diff --git a/kernel/sys.c b/kernel/sys.c
> index 7f5a0cd..433fcdb 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -37,6 +37,8 @@
>  #include <linux/ptrace.h>
>  #include <linux/fs_struct.h>
>  #include <linux/gfp.h>
> +#include <linux/cgroup.h>
> +#include <linux/init_task.h>
> 
>  #include <linux/compat.h>
>  #include <linux/syscalls.h>
> @@ -1688,8 +1690,25 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
>  			if (arg2 <= 0)
>  				current->timer_slack_ns =
>  					current->default_timer_slack_ns;
> -			else
> +			else {
> +#ifdef CONFIG_CGROUP_TIMER_SLACK
> +				/* only allow more relaxed slack value than
> +				 * the attached timer slack cgroup allows.
> +				 */
> +				unsigned long cg_timer_slack;
> +
> +				rcu_read_lock();
> +				cg_timer_slack = task_timer_slack(current)->timer_slack_ns;
> +				rcu_read_unlock();
> +				if (cg_timer_slack < arg2 || cg_timer_slack
> +					== TIMER_SLACK_NS_DEFAULT)
> +					current->timer_slack_ns = arg2;
> +				else
> +					return -EINVAL;
> +#else

Looks like this could be an inline function which returns the
minimum timer slack allowed for the task. Then the code here would be:

if (arg2 <= 0)
	current->timer_slack_ns = current->default_timer_slack_ns;
else {
	if (arg2 < min_timer_slack_ns(tsk))
		return -EINVAL; /* Can't set less than the minimum */
	current->timer_slack_ns = arg2;
}

and the #ifdef CONFIG_CGROUP_TIMER_SLACK bits could be in a header as
usual.

Incidentally, shouldn't that really be -EPERM since it's not an invalid
value -- just one that's not permitted due to restrictions imposed by
the cgroup subsystem?

>  				current->timer_slack_ns = arg2;
> +#endif
> +			}
>  			error = 0;
>  			break;
>  		case PR_MCE_KILL:
> -- 
> 1.7.0.4
> 
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> Containers at lists.linux-foundation.org
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