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cgroup: implement cgroup_subsys->implicit_on_dfl

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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: Tejun Heo <tj@kernel.org>
This commit is contained in:
Tejun Heo 2016-03-08 11:51:26 -05:00
parent e4857982f4
commit f6d635ad34
2 changed files with 44 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

13
include/linux/cgroup-defs.h
View File

@ -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

38
kernel/cgroup.c
View File

@ -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) {