linux/kernel/cgroup_freezer.c
Tejun Heo bd8815a6d8 cgroup: make css_for_each_descendant() and friends include the origin css in the iteration
Previously, all css descendant iterators didn't include the origin
(root of subtree) css in the iteration.  The reasons were maintaining
consistency with css_for_each_child() and that at the time of
introduction more use cases needed skipping the origin anyway;
however, given that css_is_descendant() considers self to be a
descendant, omitting the origin css has become more confusing and
looking at the accumulated use cases rather clearly indicates that
including origin would result in simpler code overall.

While this is a change which can easily lead to subtle bugs, cgroup
API including the iterators has recently gone through major
restructuring and no out-of-tree changes will be applicable without
adjustments making this a relatively acceptable opportunity for this
type of change.

The conversions are mostly straight-forward.  If the iteration block
had explicit origin handling before or after, it's moved inside the
iteration.  If not, if (pos == origin) continue; is added.  Some
conversions add extra reference get/put around origin handling by
consolidating origin handling and the rest.  While the extra ref
operations aren't strictly necessary, this shouldn't cause any
noticeable difference.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Acked-by: Aristeu Rozanski <aris@redhat.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Matt Helsley <matthltc@us.ibm.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Balbir Singh <bsingharora@gmail.com>
2013-08-08 20:11:27 -04:00

488 lines
13 KiB
C

/*
* cgroup_freezer.c - control group freezer subsystem
*
* Copyright IBM Corporation, 2007
*
* Author : Cedric Le Goater <clg@fr.ibm.com>
*
* 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>
/*
* 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;
spinlock_t lock;
};
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_subsys_id));
}
static struct freezer *parent_freezer(struct freezer *freezer)
{
return css_freezer(css_parent(&freezer->css));
}
bool cgroup_freezing(struct task_struct *task)
{
bool ret;
rcu_read_lock();
ret = task_freezer(task)->state & CGROUP_FREEZING;
rcu_read_unlock();
return ret;
}
/*
* cgroups_write_string() limits the size of freezer state strings to
* CGROUP_LOCAL_BUFFER_SIZE
*/
static const char *freezer_state_strs(unsigned int state)
{
if (state & CGROUP_FROZEN)
return "FROZEN";
if (state & CGROUP_FREEZING)
return "FREEZING";
return "THAWED";
};
struct cgroup_subsys freezer_subsys;
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);
spin_lock_init(&freezer->lock);
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 both parent's and our
* freezer->lock.
*/
static int freezer_css_online(struct cgroup_subsys_state *css)
{
struct freezer *freezer = css_freezer(css);
struct freezer *parent = parent_freezer(freezer);
/*
* The following double locking and freezing state inheritance
* guarantee that @cgroup can never escape ancestors' freezing
* states. See css_for_each_descendant_pre() for details.
*/
if (parent)
spin_lock_irq(&parent->lock);
spin_lock_nested(&freezer->lock, SINGLE_DEPTH_NESTING);
freezer->state |= CGROUP_FREEZER_ONLINE;
if (parent && (parent->state & CGROUP_FREEZING)) {
freezer->state |= CGROUP_FREEZING_PARENT | CGROUP_FROZEN;
atomic_inc(&system_freezing_cnt);
}
spin_unlock(&freezer->lock);
if (parent)
spin_unlock_irq(&parent->lock);
return 0;
}
/**
* freezer_css_offline - initiate destruction of a freezer css
* @css: css being destroyed
*
* @css is going away. Mark it dead and decrement system_freezing_count if
* it was holding one.
*/
static void freezer_css_offline(struct cgroup_subsys_state *css)
{
struct freezer *freezer = css_freezer(css);
spin_lock_irq(&freezer->lock);
if (freezer->state & CGROUP_FREEZING)
atomic_dec(&system_freezing_cnt);
freezer->state = 0;
spin_unlock_irq(&freezer->lock);
}
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_subsys_state *new_css,
struct cgroup_taskset *tset)
{
struct freezer *freezer = css_freezer(new_css);
struct task_struct *task;
bool clear_frozen = false;
spin_lock_irq(&freezer->lock);
/*
* 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) {
if (!(freezer->state & CGROUP_FREEZING)) {
__thaw_task(task);
} else {
freeze_task(task);
freezer->state &= ~CGROUP_FROZEN;
clear_frozen = true;
}
}
spin_unlock_irq(&freezer->lock);
/*
* Propagate FROZEN clearing upwards. We may race with
* update_if_frozen(), but as long as both work bottom-up, either
* update_if_frozen() sees child's FROZEN cleared or we clear the
* parent's FROZEN later. No parent w/ !FROZEN children can be
* left FROZEN.
*/
while (clear_frozen && (freezer = parent_freezer(freezer))) {
spin_lock_irq(&freezer->lock);
freezer->state &= ~CGROUP_FROZEN;
clear_frozen = freezer->state & CGROUP_FREEZING;
spin_unlock_irq(&freezer->lock);
}
}
static void freezer_fork(struct task_struct *task)
{
struct freezer *freezer;
rcu_read_lock();
freezer = task_freezer(task);
/*
* The root cgroup is non-freezable, so we can skip the
* following check.
*/
if (!parent_freezer(freezer))
goto out;
spin_lock_irq(&freezer->lock);
if (freezer->state & CGROUP_FREEZING)
freeze_task(task);
spin_unlock_irq(&freezer->lock);
out:
rcu_read_unlock();
}
/**
* 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;
WARN_ON_ONCE(!rcu_read_lock_held());
spin_lock_irq(&freezer->lock);
if (!(freezer->state & CGROUP_FREEZING) ||
(freezer->state & CGROUP_FROZEN))
goto out_unlock;
/* are all (live) children frozen? */
css_for_each_child(pos, css) {
struct freezer *child = css_freezer(pos);
if ((child->state & CGROUP_FREEZER_ONLINE) &&
!(child->state & CGROUP_FROZEN))
goto out_unlock;
}
/* are all tasks frozen? */
css_task_iter_start(css, &it);
while ((task = css_task_iter_next(&it))) {
if (freezing(task)) {
/*
* freezer_should_skip() indicates that the task
* should be skipped when determining freezing
* completion. Consider it frozen in addition to
* the usual frozen condition.
*/
if (!frozen(task) && !freezer_should_skip(task))
goto out_iter_end;
}
}
freezer->state |= CGROUP_FROZEN;
out_iter_end:
css_task_iter_end(&it);
out_unlock:
spin_unlock_irq(&freezer->lock);
}
static int freezer_read(struct cgroup_subsys_state *css, struct cftype *cft,
struct seq_file *m)
{
struct cgroup_subsys_state *pos;
rcu_read_lock();
/* update states bottom-up */
css_for_each_descendant_post(pos, css)
update_if_frozen(pos);
rcu_read_unlock();
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, &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, &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->lock);
if (!(freezer->state & CGROUP_FREEZER_ONLINE))
return;
if (freeze) {
if (!(freezer->state & CGROUP_FREEZING))
atomic_inc(&system_freezing_cnt);
freezer->state |= state;
freeze_cgroup(freezer);
} else {
bool was_freezing = freezer->state & CGROUP_FREEZING;
freezer->state &= ~state;
if (!(freezer->state & CGROUP_FREEZING)) {
if (was_freezing)
atomic_dec(&system_freezing_cnt);
freezer->state &= ~CGROUP_FROZEN;
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;
/*
* Update all its descendants in pre-order traversal. Each
* descendant will try to inherit its parent's FREEZING state as
* CGROUP_FREEZING_PARENT.
*/
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);
spin_lock_irq(&pos_f->lock);
if (pos_f == freezer) {
freezer_apply_state(pos_f, freeze,
CGROUP_FREEZING_SELF);
} else {
/*
* Our update to @parent->state is already visible
* which is all we need. No need to lock @parent.
* For more info on synchronization, see
* freezer_post_create().
*/
freezer_apply_state(pos_f,
parent->state & CGROUP_FREEZING,
CGROUP_FREEZING_PARENT);
}
spin_unlock_irq(&pos_f->lock);
}
rcu_read_unlock();
}
static int freezer_write(struct cgroup_subsys_state *css, struct cftype *cft,
const char *buffer)
{
bool freeze;
if (strcmp(buffer, freezer_state_strs(0)) == 0)
freeze = false;
else if (strcmp(buffer, freezer_state_strs(CGROUP_FROZEN)) == 0)
freeze = true;
else
return -EINVAL;
freezer_change_state(css_freezer(css), freeze);
return 0;
}
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,
.read_seq_string = freezer_read,
.write_string = 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_subsys = {
.name = "freezer",
.css_alloc = freezer_css_alloc,
.css_online = freezer_css_online,
.css_offline = freezer_css_offline,
.css_free = freezer_css_free,
.subsys_id = freezer_subsys_id,
.attach = freezer_attach,
.fork = freezer_fork,
.base_cftypes = files,
};