Merge branch 'for-5.2' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup

Pull cgroup updates from Tejun Heo:
 "This includes Roman's cgroup2 freezer implementation.

  It's a separate machanism from cgroup1 freezer. Instead of blocking
  user tasks in arbitrary uninterruptible sleeps, the new implementation
  extends jobctl stop - frozen tasks are trapped in jobctl stop until
  thawed and can be killed and ptraced. Lots of thanks to Oleg for
  sheperding the effort.

  Other than that, there are a few trivial changes"

* 'for-5.2' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
  cgroup: never call do_group_exit() with task->frozen bit set
  kernel: cgroup: fix misuse of %x
  cgroup: get rid of cgroup_freezer_frozen_exit()
  cgroup: prevent spurious transition into non-frozen state
  cgroup: Remove unused cgrp variable
  cgroup: document cgroup v2 freezer interface
  cgroup: add tracing points for cgroup v2 freezer
  cgroup: make TRACE_CGROUP_PATH irq-safe
  kselftests: cgroup: add freezer controller self-tests
  kselftests: cgroup: don't fail on cg_kill_all() error in cg_destroy()
  cgroup: cgroup v2 freezer
  cgroup: protect cgroup->nr_(dying_)descendants by css_set_lock
  cgroup: implement __cgroup_task_count() helper
  cgroup: rename freezer.c into legacy_freezer.c
  cgroup: remove extra cgroup_migrate_finish() call

1 files changed, 236 insertions, 403 deletions

diff --git a/kernel/cgroup/freezer.c b/kernel/cgroup/freezer.c
index 08236798d173..8cf010680678 100644
--- a/kernel/cgroup/freezer.c
+++ b/kernel/cgroup/freezer.c
@@ -1,481 +1,314 @@
-/*
- * 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>
+//SPDX-License-Identifier: GPL-2.0
 #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>
-
-/*
- * 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 */
+#include <linux/sched.h>
+#include <linux/sched/task.h>
+#include <linux/sched/signal.h>
 
-	/* mask for all FREEZING flags */
-	CGROUP_FREEZING		= CGROUP_FREEZING_SELF | CGROUP_FREEZING_PARENT,
-};
+#include "cgroup-internal.h"
 
-struct freezer {
-	struct cgroup_subsys_state	css;
-	unsigned int			state;
-};
+#include <trace/events/cgroup.h>
 
-static DEFINE_MUTEX(freezer_mutex);
-
-static inline struct freezer *css_freezer(struct cgroup_subsys_state *css)
+/*
+ * Propagate the cgroup frozen state upwards by the cgroup tree.
+ */
+static void cgroup_propagate_frozen(struct cgroup *cgrp, bool frozen)
 {
-	return css ? container_of(css, struct freezer, css) : NULL;
-}
+	int desc = 1;
 
-static inline struct freezer *task_freezer(struct task_struct *task)
-{
-	return css_freezer(task_css(task, freezer_cgrp_id));
+	/*
+	 * If the new state is frozen, some freezing ancestor cgroups may change
+	 * their state too, depending on if all their descendants are frozen.
+	 *
+	 * Otherwise, all ancestor cgroups are forced into the non-frozen state.
+	 */
+	while ((cgrp = cgroup_parent(cgrp))) {
+		if (frozen) {
+			cgrp->freezer.nr_frozen_descendants += desc;
+			if (!test_bit(CGRP_FROZEN, &cgrp->flags) &&
+			    test_bit(CGRP_FREEZE, &cgrp->flags) &&
+			    cgrp->freezer.nr_frozen_descendants ==
+			    cgrp->nr_descendants) {
+				set_bit(CGRP_FROZEN, &cgrp->flags);
+				cgroup_file_notify(&cgrp->events_file);
+				TRACE_CGROUP_PATH(notify_frozen, cgrp, 1);
+				desc++;
+			}
+		} else {
+			cgrp->freezer.nr_frozen_descendants -= desc;
+			if (test_bit(CGRP_FROZEN, &cgrp->flags)) {
+				clear_bit(CGRP_FROZEN, &cgrp->flags);
+				cgroup_file_notify(&cgrp->events_file);
+				TRACE_CGROUP_PATH(notify_frozen, cgrp, 0);
+				desc++;
+			}
+		}
+	}
 }
 
-static struct freezer *parent_freezer(struct freezer *freezer)
+/*
+ * Revisit the cgroup frozen state.
+ * Checks if the cgroup is really frozen and perform all state transitions.
+ */
+void cgroup_update_frozen(struct cgroup *cgrp)
 {
-	return css_freezer(freezer->css.parent);
-}
+	bool frozen;
 
-bool cgroup_freezing(struct task_struct *task)
-{
-	bool ret;
+	lockdep_assert_held(&css_set_lock);
 
-	rcu_read_lock();
-	ret = task_freezer(task)->state & CGROUP_FREEZING;
-	rcu_read_unlock();
+	/*
+	 * If the cgroup has to be frozen (CGRP_FREEZE bit set),
+	 * and all tasks are frozen and/or stopped, let's consider
+	 * the cgroup frozen. Otherwise it's not frozen.
+	 */
+	frozen = test_bit(CGRP_FREEZE, &cgrp->flags) &&
+		cgrp->freezer.nr_frozen_tasks == __cgroup_task_count(cgrp);
 
-	return ret;
-}
+	if (frozen) {
+		/* Already there? */
+		if (test_bit(CGRP_FROZEN, &cgrp->flags))
+			return;
 
-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;
+		set_bit(CGRP_FROZEN, &cgrp->flags);
+	} else {
+		/* Already there? */
+		if (!test_bit(CGRP_FROZEN, &cgrp->flags))
+			return;
 
-	freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL);
-	if (!freezer)
-		return ERR_PTR(-ENOMEM);
+		clear_bit(CGRP_FROZEN, &cgrp->flags);
+	}
+	cgroup_file_notify(&cgrp->events_file);
+	TRACE_CGROUP_PATH(notify_frozen, cgrp, frozen);
 
-	return &freezer->css;
+	/* Update the state of ancestor cgroups. */
+	cgroup_propagate_frozen(cgrp, frozen);
 }
 
-/**
- * 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.
+/*
+ * Increment cgroup's nr_frozen_tasks.
  */
-static int freezer_css_online(struct cgroup_subsys_state *css)
+static void cgroup_inc_frozen_cnt(struct cgroup *cgrp)
 {
-	struct freezer *freezer = css_freezer(css);
-	struct freezer *parent = parent_freezer(freezer);
-
-	mutex_lock(&freezer_mutex);
-
-	freezer->state |= CGROUP_FREEZER_ONLINE;
-
-	if (parent && (parent->state & CGROUP_FREEZING)) {
-		freezer->state |= CGROUP_FREEZING_PARENT | CGROUP_FROZEN;
-		atomic_inc(&system_freezing_cnt);
-	}
-
-	mutex_unlock(&freezer_mutex);
-	return 0;
+	cgrp->freezer.nr_frozen_tasks++;
 }
 
-/**
- * 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.
+/*
+ * Decrement cgroup's nr_frozen_tasks.
  */
-static void freezer_css_offline(struct cgroup_subsys_state *css)
+static void cgroup_dec_frozen_cnt(struct cgroup *cgrp)
 {
-	struct freezer *freezer = css_freezer(css);
-
-	mutex_lock(&freezer_mutex);
-
-	if (freezer->state & CGROUP_FREEZING)
-		atomic_dec(&system_freezing_cnt);
-
-	freezer->state = 0;
-
-	mutex_unlock(&freezer_mutex);
+	cgrp->freezer.nr_frozen_tasks--;
+	WARN_ON_ONCE(cgrp->freezer.nr_frozen_tasks < 0);
 }
 
-static void freezer_css_free(struct cgroup_subsys_state *css)
+/*
+ * Enter frozen/stopped state, if not yet there. Update cgroup's counters,
+ * and revisit the state of the cgroup, if necessary.
+ */
+void cgroup_enter_frozen(void)
 {
-	kfree(css_freezer(css));
+	struct cgroup *cgrp;
+
+	if (current->frozen)
+		return;
+
+	spin_lock_irq(&css_set_lock);
+	current->frozen = true;
+	cgrp = task_dfl_cgroup(current);
+	cgroup_inc_frozen_cnt(cgrp);
+	cgroup_update_frozen(cgrp);
+	spin_unlock_irq(&css_set_lock);
 }
 
 /*
- * 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.
+ * Conditionally leave frozen/stopped state. Update cgroup's counters,
+ * and revisit the state of the cgroup, if necessary.
  *
- * 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.
+ * If always_leave is not set, and the cgroup is freezing,
+ * we're racing with the cgroup freezing. In this case, we don't
+ * drop the frozen counter to avoid a transient switch to
+ * the unfrozen state.
  */
-static void freezer_attach(struct cgroup_taskset *tset)
+void cgroup_leave_frozen(bool always_leave)
 {
-	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);
-			}
-		}
+	struct cgroup *cgrp;
+
+	spin_lock_irq(&css_set_lock);
+	cgrp = task_dfl_cgroup(current);
+	if (always_leave || !test_bit(CGRP_FREEZE, &cgrp->flags)) {
+		cgroup_dec_frozen_cnt(cgrp);
+		cgroup_update_frozen(cgrp);
+		WARN_ON_ONCE(!current->frozen);
+		current->frozen = false;
+	} else if (!(current->jobctl & JOBCTL_TRAP_FREEZE)) {
+		spin_lock(&current->sighand->siglock);
+		current->jobctl |= JOBCTL_TRAP_FREEZE;
+		set_thread_flag(TIF_SIGPENDING);
+		spin_unlock(&current->sighand->siglock);
 	}
-
-	mutex_unlock(&freezer_mutex);
+	spin_unlock_irq(&css_set_lock);
 }
 
-/**
- * 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.
+/*
+ * Freeze or unfreeze the task by setting or clearing the JOBCTL_TRAP_FREEZE
+ * jobctl bit.
  */
-static void freezer_fork(struct task_struct *task)
+static void cgroup_freeze_task(struct task_struct *task, bool freeze)
 {
-	struct freezer *freezer;
+	unsigned long flags;
 
-	/*
-	 * 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))
+	/* If the task is about to die, don't bother with freezing it. */
+	if (!lock_task_sighand(task, &flags))
 		return;
 
-	mutex_lock(&freezer_mutex);
-	rcu_read_lock();
-
-	freezer = task_freezer(task);
-	if (freezer->state & CGROUP_FREEZING)
-		freeze_task(task);
+	if (freeze) {
+		task->jobctl |= JOBCTL_TRAP_FREEZE;
+		signal_wake_up(task, false);
+	} else {
+		task->jobctl &= ~JOBCTL_TRAP_FREEZE;
+		wake_up_process(task);
+	}
 
-	rcu_read_unlock();
-	mutex_unlock(&freezer_mutex);
+	unlock_task_sighand(task, &flags);
 }
 
-/**
- * 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.
+/*
+ * Freeze or unfreeze all tasks in the given cgroup.
  */
-static void update_if_frozen(struct cgroup_subsys_state *css)
+static void cgroup_do_freeze(struct cgroup *cgrp, bool freeze)
 {
-	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;
+	lockdep_assert_held(&cgroup_mutex);
 
-	/* 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();
+	spin_lock_irq(&css_set_lock);
+	if (freeze)
+		set_bit(CGRP_FREEZE, &cgrp->flags);
+	else
+		clear_bit(CGRP_FREEZE, &cgrp->flags);
+	spin_unlock_irq(&css_set_lock);
 
-	/* are all tasks frozen? */
-	css_task_iter_start(css, 0, &it);
+	if (freeze)
+		TRACE_CGROUP_PATH(freeze, cgrp);
+	else
+		TRACE_CGROUP_PATH(unfreeze, cgrp);
 
+	css_task_iter_start(&cgrp->self, 0, &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);
-}
-
-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))
+		/*
+		 * Ignore kernel threads here. Freezing cgroups containing
+		 * kthreads isn't supported.
+		 */
+		if (task->flags & PF_KTHREAD)
 			continue;
-		rcu_read_unlock();
-
-		update_if_frozen(pos);
-
-		rcu_read_lock();
-		css_put(pos);
+		cgroup_freeze_task(task, freeze);
 	}
-
-	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);
+	/*
+	 * Cgroup state should be revisited here to cover empty leaf cgroups
+	 * and cgroups which descendants are already in the desired state.
+	 */
+	spin_lock_irq(&css_set_lock);
+	if (cgrp->nr_descendants == cgrp->freezer.nr_frozen_descendants)
+		cgroup_update_frozen(cgrp);
+	spin_unlock_irq(&css_set_lock);
 }
 
-/**
- * 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.
+/*
+ * Adjust the task state (freeze or unfreeze) and revisit the state of
+ * source and destination cgroups.
  */
-static void freezer_apply_state(struct freezer *freezer, bool freeze,
-				unsigned int state)
+void cgroup_freezer_migrate_task(struct task_struct *task,
+				 struct cgroup *src, struct cgroup *dst)
 {
-	/* also synchronizes against task migration, see freezer_attach() */
-	lockdep_assert_held(&freezer_mutex);
+	lockdep_assert_held(&css_set_lock);
 
-	if (!(freezer->state & CGROUP_FREEZER_ONLINE))
+	/*
+	 * Kernel threads are not supposed to be frozen at all.
+	 */
+	if (task->flags & PF_KTHREAD)
 		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);
-		}
+	/*
+	 * Adjust counters of freezing and frozen tasks.
+	 * Note, that if the task is frozen, but the destination cgroup is not
+	 * frozen, we bump both counters to keep them balanced.
+	 */
+	if (task->frozen) {
+		cgroup_inc_frozen_cnt(dst);
+		cgroup_dec_frozen_cnt(src);
 	}
-}
-
-/**
- * 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;
+	cgroup_update_frozen(dst);
+	cgroup_update_frozen(src);
 
 	/*
-	 * Update all its descendants in pre-order traversal.  Each
-	 * descendant will try to inherit its parent's FREEZING state as
-	 * CGROUP_FREEZING_PARENT.
+	 * Force the task to the desired state.
 	 */
-	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);
+	cgroup_freeze_task(task, test_bit(CGRP_FREEZE, &dst->flags));
 }
 
-static ssize_t freezer_write(struct kernfs_open_file *of,
-			     char *buf, size_t nbytes, loff_t off)
+void cgroup_freeze(struct cgroup *cgrp, bool freeze)
 {
-	bool freeze;
+	struct cgroup_subsys_state *css;
+	struct cgroup *dsct;
+	bool applied = false;
 
-	buf = strstrip(buf);
+	lockdep_assert_held(&cgroup_mutex);
 
-	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;
+	/*
+	 * Nothing changed? Just exit.
+	 */
+	if (cgrp->freezer.freeze == freeze)
+		return;
 
-	freezer_change_state(css_freezer(of_css(of)), freeze);
-	return nbytes;
-}
+	cgrp->freezer.freeze = freeze;
 
-static u64 freezer_self_freezing_read(struct cgroup_subsys_state *css,
-				      struct cftype *cft)
-{
-	struct freezer *freezer = css_freezer(css);
+	/*
+	 * Propagate changes downwards the cgroup tree.
+	 */
+	css_for_each_descendant_pre(css, &cgrp->self) {
+		dsct = css->cgroup;
 
-	return (bool)(freezer->state & CGROUP_FREEZING_SELF);
-}
+		if (cgroup_is_dead(dsct))
+			continue;
 
-static u64 freezer_parent_freezing_read(struct cgroup_subsys_state *css,
-					struct cftype *cft)
-{
-	struct freezer *freezer = css_freezer(css);
+		if (freeze) {
+			dsct->freezer.e_freeze++;
+			/*
+			 * Already frozen because of ancestor's settings?
+			 */
+			if (dsct->freezer.e_freeze > 1)
+				continue;
+		} else {
+			dsct->freezer.e_freeze--;
+			/*
+			 * Still frozen because of ancestor's settings?
+			 */
+			if (dsct->freezer.e_freeze > 0)
+				continue;
 
-	return (bool)(freezer->state & CGROUP_FREEZING_PARENT);
-}
+			WARN_ON_ONCE(dsct->freezer.e_freeze < 0);
+		}
+
+		/*
+		 * Do change actual state: freeze or unfreeze.
+		 */
+		cgroup_do_freeze(dsct, freeze);
+		applied = true;
+	}
 
-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,
-};
+	/*
+	 * Even if the actual state hasn't changed, let's notify a user.
+	 * The state can be enforced by an ancestor cgroup: the cgroup
+	 * can already be in the desired state or it can be locked in the
+	 * opposite state, so that the transition will never happen.
+	 * In both cases it's better to notify a user, that there is
+	 * nothing to wait for.
+	 */
+	if (!applied) {
+		TRACE_CGROUP_PATH(notify_frozen, cgrp,
+				  test_bit(CGRP_FROZEN, &cgrp->flags));
+		cgroup_file_notify(&cgrp->events_file);
+	}
+}