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Commit f6d635ad authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: implement cgroup_subsys->implicit_on_dfl 



Some controllers, perf_event for now and possibly freezer in the
future, don't really make sense to control explicitly through
"cgroup.subtree_control".  For example, the primary role of perf_event
is identifying the cgroups of tasks; however, because the controller
also keeps a small amount of state per cgroup, it can't be replaced
with simple cgroup membership tests.

This patch implements cgroup_subsys->implicit_on_dfl flag.  When set,
the controller is implicitly enabled on all cgroups on the v2
hierarchy so that utility type controllers such as perf_event can be
enabled and function transparently.

An implicit controller doesn't show up in "cgroup.controllers" or
"cgroup.subtree_control", is exempt from no internal process rule and
can be stolen from the default hierarchy even if there are non-root
csses.

v2: Reimplemented on top of the recent updates to css handling and
    subsystem rebinding.  Rebinding implicit subsystems is now a
    simple matter of exempting it from the busy subsystem check.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent e4857982

include/linux/cgroup-defs.h

+13 −0
Original line number Diff line number Diff line
@@ -450,6 +450,19 @@ struct cgroup_subsys { 


	bool early_init:1;



	/*

	 * If %true, the controller, on the default hierarchy, doesn't show

	 * up in "cgroup.controllers" or "cgroup.subtree_control", is

	 * implicitly enabled on all cgroups on the default hierarchy, and

	 * bypasses the "no internal process" constraint.  This is for

	 * utility type controllers which is transparent to userland.

	 *

	 * An implicit controller can be stolen from the default hierarchy

	 * anytime and thus must be okay with offline csses from previous

	 * hierarchies coexisting with csses for the current one.

	 */

	bool implicit_on_dfl:1;



	/*

	 * If %false, this subsystem is properly hierarchical -

	 * configuration, resource accounting and restriction on a parent

kernel/cgroup.c

+31 −7
Original line number Diff line number Diff line
@@ -186,6 +186,9 @@ static u16 cgroup_no_v1_mask; 
/* some controllers are not supported in the default hierarchy */

static u16 cgrp_dfl_inhibit_ss_mask;



/* some controllers are implicitly enabled on the default hierarchy */

static unsigned long cgrp_dfl_implicit_ss_mask;



/* The list of hierarchy roots */



static LIST_HEAD(cgroup_roots);
@@ -359,8 +362,8 @@ static u16 cgroup_control(struct cgroup *cgrp) 
		return parent->subtree_control;



	if (cgroup_on_dfl(cgrp))

		root_ss_mask &= ~cgrp_dfl_inhibit_ss_mask;



		root_ss_mask &= ~(cgrp_dfl_inhibit_ss_mask |

				  cgrp_dfl_implicit_ss_mask);

	return root_ss_mask;

}
@@ -1327,6 +1330,8 @@ static u16 cgroup_calc_subtree_ss_mask(u16 subtree_control, u16 this_ss_mask) 


	lockdep_assert_held(&cgroup_mutex);



	cur_ss_mask |= cgrp_dfl_implicit_ss_mask;



	while (true) {

		u16 new_ss_mask = cur_ss_mask;
@@ -1512,8 +1517,13 @@ static int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask) 
	lockdep_assert_held(&cgroup_mutex);



	do_each_subsys_mask(ss, ssid, ss_mask) {

		/* if @ss has non-root csses attached to it, can't move */

		if (css_next_child(NULL, cgroup_css(&ss->root->cgrp, ss)))

		/*

		 * If @ss has non-root csses attached to it, can't move.

		 * If @ss is an implicit controller, it is exempt from this

		 * rule and can be stolen.

		 */

		if (css_next_child(NULL, cgroup_css(&ss->root->cgrp, ss)) &&

		    !ss->implicit_on_dfl)

			return -EBUSY;



		/* can't move between two non-dummy roots either */
@@ -3039,6 +3049,18 @@ static void cgroup_restore_control(struct cgroup *cgrp) 
	}

}



static bool css_visible(struct cgroup_subsys_state *css)

{

	struct cgroup_subsys *ss = css->ss;

	struct cgroup *cgrp = css->cgroup;



	if (cgroup_control(cgrp) & (1 << ss->id))

		return true;

	if (!(cgroup_ss_mask(cgrp) & (1 << ss->id)))

		return false;

	return cgroup_on_dfl(cgrp) && ss->implicit_on_dfl;

}



/**

 * cgroup_apply_control_enable - enable or show csses according to control

 * @cgrp: root of the target subtree
@@ -3074,7 +3096,7 @@ static int cgroup_apply_control_enable(struct cgroup *cgrp) 
					return PTR_ERR(css);

			}



			if (cgroup_control(dsct) & (1 << ss->id)) {

			if (css_visible(css)) {

				ret = css_populate_dir(css);

				if (ret)

					return ret;
@@ -3117,7 +3139,7 @@ static void cgroup_apply_control_disable(struct cgroup *cgrp) 
			if (css->parent &&

			    !(cgroup_ss_mask(dsct) & (1 << ss->id))) {

				kill_css(css);

			} else if (!(cgroup_control(dsct) & (1 << ss->id))) {

			} else if (!css_visible(css)) {

				css_clear_dir(css);

				if (ss->css_reset)

					ss->css_reset(css);
@@ -5455,7 +5477,9 @@ int __init cgroup_init(void) 


		cgrp_dfl_root.subsys_mask |= 1 << ss->id;



		if (!ss->dfl_cftypes)

		if (ss->implicit_on_dfl)

			cgrp_dfl_implicit_ss_mask |= 1 << ss->id;

		else if (!ss->dfl_cftypes)

			cgrp_dfl_inhibit_ss_mask |= 1 << ss->id;



		if (ss->dfl_cftypes == ss->legacy_cftypes) {