/*
* cgroup_freezer.c - control group freezer subsystem
*
* Copyright IBM Corporation, 2007
*
* Author : Cedric Le Goater <[email protected]>
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of version 2.1 of the GNU Lesser General Public License
* as published by the Free Software Foundation.
*
* This program is distributed in the hope that it would be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
*/
#include <linux/export.h>
#include <linux/slab.h>
#include <linux/cgroup.h>
#include <linux/fs.h>
#include <linux/uaccess.h>
#include <linux/freezer.h>
#include <linux/seq_file.h>
#include <linux/mutex.h>
#include <linux/cpu.h>
/*
* A cgroup is freezing if any FREEZING flags are set. FREEZING_SELF is
* set if "FROZEN" is written to freezer.state cgroupfs file, and cleared
* for "THAWED". FREEZING_PARENT is set if the parent freezer is FREEZING
* for whatever reason. IOW, a cgroup has FREEZING_PARENT set if one of
* its ancestors has FREEZING_SELF set.
*/
enum freezer_state_flags {
CGROUP_FREEZER_ONLINE = (1 << 0), /* freezer is fully online */
CGROUP_FREEZING_SELF = (1 << 1), /* this freezer is freezing */
CGROUP_FREEZING_PARENT = (1 << 2), /* the parent freezer is freezing */
CGROUP_FROZEN = (1 << 3), /* this and its descendants frozen */
/* mask for all FREEZING flags */
CGROUP_FREEZING = CGROUP_FREEZING_SELF | CGROUP_FREEZING_PARENT,
};
struct freezer {
struct cgroup_subsys_state css;
unsigned int state;
};
static DEFINE_MUTEX(freezer_mutex);
static inline struct freezer *css_freezer(struct cgroup_subsys_state *css)
{
return css ? container_of(css, struct freezer, css) : NULL;
}
static inline struct freezer *task_freezer(struct task_struct *task)
{
return css_freezer(task_css(task, freezer_cgrp_id));
}
static struct freezer *parent_freezer(struct freezer *freezer)
{
return css_freezer(freezer->css.parent);
}
bool cgroup_freezing(struct task_struct *task)
{
bool ret;
unsigned int state;
rcu_read_lock();
/* Check if the cgroup is still FREEZING, but not FROZEN. The extra
* !FROZEN check is required, because the FREEZING bit is not cleared
* when the state FROZEN is reached.
*/
state = task_freezer(task)->state;
ret = (state & CGROUP_FREEZING) && !(state & CGROUP_FROZEN);
rcu_read_unlock();
return ret;
}
static const char *freezer_state_strs(unsigned int state)
{
if (state & CGROUP_FROZEN)
return "FROZEN";
if (state & CGROUP_FREEZING)
return "FREEZING";
return "THAWED";
};
static struct cgroup_subsys_state *
freezer_css_alloc(struct cgroup_subsys_state *parent_css)
{
struct freezer *freezer;
freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL);
if (!freezer)
return ERR_PTR(-ENOMEM);
return &freezer->css;
}
/**
* freezer_css_online - commit creation of a freezer css
* @css: css being created
*
* We're committing to creation of @css. Mark it online and inherit
* parent's freezing state while holding cpus read lock and freezer_mutex.
*/
static int freezer_css_online(struct cgroup_subsys_state *css)
{
struct freezer *freezer = css_freezer(css);
struct freezer *parent = parent_freezer(freezer);
cpus_read_lock();
mutex_lock(&freezer_mutex);
freezer->state |= CGROUP_FREEZER_ONLINE;
if (parent && (parent->state & CGROUP_FREEZING)) {
freezer->state |= CGROUP_FREEZING_PARENT | CGROUP_FROZEN;
static_branch_inc_cpuslocked(&freezer_active);
}
mutex_unlock(&freezer_mutex);
cpus_read_unlock();
return 0;
}
/**
* freezer_css_offline - initiate destruction of a freezer css
* @css: css being destroyed
*
* @css is going away. Mark it dead and decrement freezer_active if
* it was holding one.
*/
static void freezer_css_offline(struct cgroup_subsys_state *css)
{
struct freezer *freezer = css_freezer(css);
cpus_read_lock();
mutex_lock(&freezer_mutex);
if (freezer->state & CGROUP_FREEZING)
static_branch_dec_cpuslocked(&freezer_active);
freezer->state = 0;
mutex_unlock(&freezer_mutex);
cpus_read_unlock();
}
static void freezer_css_free(struct cgroup_subsys_state *css)
{
kfree(css_freezer(css));
}
/*
* Tasks can be migrated into a different freezer anytime regardless of its
* current state. freezer_attach() is responsible for making new tasks
* conform to the current state.
*
* Freezer state changes and task migration are synchronized via
* @freezer->lock. freezer_attach() makes the new tasks conform to the
* current state and all following state changes can see the new tasks.
*/
static void freezer_attach(struct cgroup_taskset *tset)
{
struct task_struct *task;
struct cgroup_subsys_state *new_css;
mutex_lock(&freezer_mutex);
/*
* Make the new tasks conform to the current state of @new_css.
* For simplicity, when migrating any task to a FROZEN cgroup, we
* revert it to FREEZING and let update_if_frozen() determine the
* correct state later.
*
* Tasks in @tset are on @new_css but may not conform to its
* current state before executing the following - !frozen tasks may
* be visible in a FROZEN cgroup and frozen tasks in a THAWED one.
*/
cgroup_taskset_for_each(task, new_css, tset) {
struct freezer *freezer = css_freezer(new_css);
if (!(freezer->state & CGROUP_FREEZING)) {
__thaw_task(task);
} else {
freeze_task(task);
/* clear FROZEN and propagate upwards */
while (freezer && (freezer->state & CGROUP_FROZEN)) {
freezer->state &= ~CGROUP_FROZEN;
freezer = parent_freezer(freezer);
}
}
}
mutex_unlock(&freezer_mutex);
}
/**
* freezer_fork - cgroup post fork callback
* @task: a task which has just been forked
*
* @task has just been created and should conform to the current state of
* the cgroup_freezer it belongs to. This function may race against
* freezer_attach(). Losing to freezer_attach() means that we don't have
* to do anything as freezer_attach() will put @task into the appropriate
* state.
*/
static void freezer_fork(struct task_struct *task)
{
struct freezer *freezer;
/*
* The root cgroup is non-freezable, so we can skip locking the
* freezer. This is safe regardless of race with task migration.
* If we didn't race or won, skipping is obviously the right thing
* to do. If we lost and root is the new cgroup, noop is still the
* right thing to do.
*/
if (task_css_is_root(task, freezer_cgrp_id))
return;
mutex_lock(&freezer_mutex);
rcu_read_lock();
freezer = task_freezer(task);
if (freezer->state & CGROUP_FREEZING)
freeze_task(task);
rcu_read_unlock();
mutex_unlock(&freezer_mutex);
}
/**
* update_if_frozen - update whether a cgroup finished freezing
* @css: css of interest
*
* Once FREEZING is initiated, transition to FROZEN is lazily updated by
* calling this function. If the current state is FREEZING but not FROZEN,
* this function checks whether all tasks of this cgroup and the descendant
* cgroups finished freezing and, if so, sets FROZEN.
*
* The caller is responsible for grabbing RCU read lock and calling
* update_if_frozen() on all descendants prior to invoking this function.
*
* Task states and freezer state might disagree while tasks are being
* migrated into or out of @css, so we can't verify task states against
* @freezer state here. See freezer_attach() for details.
*/
static void update_if_frozen(struct cgroup_subsys_state *css)
{
struct freezer *freezer = css_freezer(css);
struct cgroup_subsys_state *pos;
struct css_task_iter it;
struct task_struct *task;
lockdep_assert_held(&freezer_mutex);
if (!(freezer->state & CGROUP_FREEZING) ||
(freezer->state & CGROUP_FROZEN))
return;
/* are all (live) children frozen? */
rcu_read_lock();
css_for_each_child(pos, css) {
struct freezer *child = css_freezer(pos);
if ((child->state & CGROUP_FREEZER_ONLINE) &&
!(child->state & CGROUP_FROZEN)) {
rcu_read_unlock();
return;
}
}
rcu_read_unlock();
/* are all tasks frozen? */
css_task_iter_start(css, 0, &it);
while ((task = css_task_iter_next(&it))) {
if (freezing(task) && !frozen(task))
goto out_iter_end;
}
freezer->state |= CGROUP_FROZEN;
out_iter_end:
css_task_iter_end(&it);
}
static int freezer_read(struct seq_file *m, void *v)
{
struct cgroup_subsys_state *css = seq_css(m), *pos;
mutex_lock(&freezer_mutex);
rcu_read_lock();
/* update states bottom-up */
css_for_each_descendant_post(pos, css) {
if (!css_tryget_online(pos))
continue;
rcu_read_unlock();
update_if_frozen(pos);
rcu_read_lock();
css_put(pos);
}
rcu_read_unlock();
mutex_unlock(&freezer_mutex);
seq_puts(m, freezer_state_strs(css_freezer(css)->state));
seq_putc(m, '\n');
return 0;
}
static void freeze_cgroup(struct freezer *freezer)
{
struct css_task_iter it;
struct task_struct *task;
css_task_iter_start(&freezer->css, 0, &it);
while ((task = css_task_iter_next(&it)))
freeze_task(task);
css_task_iter_end(&it);
}
static void unfreeze_cgroup(struct freezer *freezer)
{
struct css_task_iter it;
struct task_struct *task;
css_task_iter_start(&freezer->css, 0, &it);
while ((task = css_task_iter_next(&it)))
__thaw_task(task);
css_task_iter_end(&it);
}
/**
* freezer_apply_state - apply state change to a single cgroup_freezer
* @freezer: freezer to apply state change to
* @freeze: whether to freeze or unfreeze
* @state: CGROUP_FREEZING_* flag to set or clear
*
* Set or clear @state on @cgroup according to @freeze, and perform
* freezing or thawing as necessary.
*/
static void freezer_apply_state(struct freezer *freezer, bool freeze,
unsigned int state)
{
/* also synchronizes against task migration, see freezer_attach() */
lockdep_assert_held(&freezer_mutex);
if (!(freezer->state & CGROUP_FREEZER_ONLINE))
return;
if (freeze) {
if (!(freezer->state & CGROUP_FREEZING))
static_branch_inc_cpuslocked(&freezer_active);
freezer->state |= state;
freeze_cgroup(freezer);
} else {
bool was_freezing = freezer->state & CGROUP_FREEZING;
freezer->state &= ~state;
if (!(freezer->state & CGROUP_FREEZING)) {
freezer->state &= ~CGROUP_FROZEN;
if (was_freezing)
static_branch_dec_cpuslocked(&freezer_active);
unfreeze_cgroup(freezer);
}
}
}
/**
* freezer_change_state - change the freezing state of a cgroup_freezer
* @freezer: freezer of interest
* @freeze: whether to freeze or thaw
*
* Freeze or thaw @freezer according to @freeze. The operations are
* recursive - all descendants of @freezer will be affected.
*/
static void freezer_change_state(struct freezer *freezer, bool freeze)
{
struct cgroup_subsys_state *pos;
cpus_read_lock();
/*
* Update all its descendants in pre-order traversal. Each
* descendant will try to inherit its parent's FREEZING state as
* CGROUP_FREEZING_PARENT.
*/
mutex_lock(&freezer_mutex);
rcu_read_lock();
css_for_each_descendant_pre(pos, &freezer->css) {
struct freezer *pos_f = css_freezer(pos);
struct freezer *parent = parent_freezer(pos_f);
if (!css_tryget_online(pos))
continue;
rcu_read_unlock();
if (pos_f == freezer)
freezer_apply_state(pos_f, freeze,
CGROUP_FREEZING_SELF);
else
freezer_apply_state(pos_f,
parent->state & CGROUP_FREEZING,
CGROUP_FREEZING_PARENT);
rcu_read_lock();
css_put(pos);
}
rcu_read_unlock();
mutex_unlock(&freezer_mutex);
cpus_read_unlock();
}
static ssize_t freezer_write(struct kernfs_open_file *of,
char *buf, size_t nbytes, loff_t off)
{
bool freeze;
buf = strstrip(buf);
if (strcmp(buf, freezer_state_strs(0)) == 0)
freeze = false;
else if (strcmp(buf, freezer_state_strs(CGROUP_FROZEN)) == 0)
freeze = true;
else
return -EINVAL;
freezer_change_state(css_freezer(of_css(of)), freeze);
return nbytes;
}
static u64 freezer_self_freezing_read(struct cgroup_subsys_state *css,
struct cftype *cft)
{
struct freezer *freezer = css_freezer(css);
return (bool)(freezer->state & CGROUP_FREEZING_SELF);
}
static u64 freezer_parent_freezing_read(struct cgroup_subsys_state *css,
struct cftype *cft)
{
struct freezer *freezer = css_freezer(css);
return (bool)(freezer->state & CGROUP_FREEZING_PARENT);
}
static struct cftype files[] = {
{
.name = "state",
.flags = CFTYPE_NOT_ON_ROOT,
.seq_show = freezer_read,
.write = freezer_write,
},
{
.name = "self_freezing",
.flags = CFTYPE_NOT_ON_ROOT,
.read_u64 = freezer_self_freezing_read,
},
{
.name = "parent_freezing",
.flags = CFTYPE_NOT_ON_ROOT,
.read_u64 = freezer_parent_freezing_read,
},
{ } /* terminate */
};
struct cgroup_subsys freezer_cgrp_subsys = {
.css_alloc = freezer_css_alloc,
.css_online = freezer_css_online,
.css_offline = freezer_css_offline,
.css_free = freezer_css_free,
.attach = freezer_attach,
.fork = freezer_fork,
.legacy_cftypes = files,
};
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