[PATCH 0/5] freezer for cgroup v2

[PATCH 0/5] freezer for cgroup v2

[Roman Gushchin]

This patchset implements freezer for cgroup v2.

It provides similar functionality as v1 freezer, but the interface
conforms to the cgroup v2 interface design principles, and it
provides a better user experience: tasks can be killed, ptrace works,
there is no separate controller, which has to be enabled, etc.

Patches (1) and (2) are some preparational work, patch (3) contains
the implementation, patch (4) is a small cgroup kselftest fix,
patch (5) covers freezer adds 6 new kselftests to cover the freezer
functionality.

Roman Gushchin (5):
  cgroup: rename freezer.c into legacy_freezer.c
  cgroup: implement __cgroup_task_count() helper
  cgroup: cgroup v2 freezer
  kselftests: cgroup: don't fail on cg_kill_all() error in cg_destroy()
  kselftests: cgroup: add freezer controller self-tests

 include/linux/cgroup-defs.h                   |  33 +
 include/linux/cgroup.h                        |  42 ++
 include/linux/sched.h                         |   5 +-
 include/linux/sched/jobctl.h                  |   5 +-
 kernel/cgroup/Makefile                        |   4 +-
 kernel/cgroup/cgroup-internal.h               |   1 +
 kernel/cgroup/cgroup-v1.c                     |  16 -
 kernel/cgroup/cgroup.c                        | 132 +++-
 kernel/cgroup/freezer.c                       | 590 +++++----------
 kernel/cgroup/legacy_freezer.c                | 481 ++++++++++++
 kernel/ptrace.c                               |   6 +
 kernel/signal.c                               |  51 +-
 tools/testing/selftests/cgroup/.gitignore     |   1 +
 tools/testing/selftests/cgroup/Makefile       |   2 +
 tools/testing/selftests/cgroup/cgroup_util.c  |  85 ++-
 tools/testing/selftests/cgroup/cgroup_util.h  |   7 +
 tools/testing/selftests/cgroup/test_freezer.c | 685 ++++++++++++++++++
 17 files changed, 1695 insertions(+), 451 deletions(-)
 create mode 100644 kernel/cgroup/legacy_freezer.c
 create mode 100644 tools/testing/selftests/cgroup/test_freezer.c

-- 
2.17.2

[PATCH 1/5] cgroup: rename freezer.c into legacy_freezer.c

[Roman Gushchin]

Freezer.c will contain an implementation of cgroup v2 freezer,
so let's rename the v1 freezer to avoid naming conflicts.

Signed-off-by: Roman Gushchin <guro@fb.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: kernel-team@fb.com
---
 kernel/cgroup/Makefile                        | 2 +-
 kernel/cgroup/{freezer.c => legacy_freezer.c} | 0
 2 files changed, 1 insertion(+), 1 deletion(-)
 rename kernel/cgroup/{freezer.c => legacy_freezer.c} (100%)

diff --git a/kernel/cgroup/Makefile b/kernel/cgroup/Makefile
index bfcdae896122..8d5689ca94b9 100644
--- a/kernel/cgroup/Makefile
+++ b/kernel/cgroup/Makefile
@@ -1,7 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0
 obj-y := cgroup.o rstat.o namespace.o cgroup-v1.o
 
-obj-$(CONFIG_CGROUP_FREEZER) += freezer.o
+obj-$(CONFIG_CGROUP_FREEZER) += legacy_freezer.o
 obj-$(CONFIG_CGROUP_PIDS) += pids.o
 obj-$(CONFIG_CGROUP_RDMA) += rdma.o
 obj-$(CONFIG_CPUSETS) += cpuset.o
diff --git a/kernel/cgroup/freezer.c b/kernel/cgroup/legacy_freezer.c
similarity index 100%
rename from kernel/cgroup/freezer.c
rename to kernel/cgroup/legacy_freezer.c
-- 
2.17.2

[PATCH 2/5] cgroup: implement __cgroup_task_count() helper

[Roman Gushchin]

The helper is identical to the existing cgroup_task_count()
except it doesn't take the css_set_lock by itself, assuming
that the caller does.

Also, move cgroup_task_count() implementation into
kernel/cgroup/cgroup.c, as there is nothing specific to cgroup v1.

Signed-off-by: Roman Gushchin <guro@fb.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: kernel-team@fb.com
---
 kernel/cgroup/cgroup-internal.h |  1 +
 kernel/cgroup/cgroup-v1.c       | 16 ----------------
 kernel/cgroup/cgroup.c          | 33 +++++++++++++++++++++++++++++++++
 3 files changed, 34 insertions(+), 16 deletions(-)

diff --git a/kernel/cgroup/cgroup-internal.h b/kernel/cgroup/cgroup-internal.h
index 75568fcf2180..fe01a9fa4a8d 100644
--- a/kernel/cgroup/cgroup-internal.h
+++ b/kernel/cgroup/cgroup-internal.h
@@ -224,6 +224,7 @@ int cgroup_rmdir(struct kernfs_node *kn);
 int cgroup_show_path(struct seq_file *sf, struct kernfs_node *kf_node,
 		     struct kernfs_root *kf_root);
 
+int __cgroup_task_count(const struct cgroup *cgrp);
 int cgroup_task_count(const struct cgroup *cgrp);
 
 /*
diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
index 51063e7a93c2..6134fef07d57 100644
--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c
@@ -336,22 +336,6 @@ static struct cgroup_pidlist *cgroup_pidlist_find_create(struct cgroup *cgrp,
 	return l;
 }
 
-/**
- * cgroup_task_count - count the number of tasks in a cgroup.
- * @cgrp: the cgroup in question
- */
-int cgroup_task_count(const struct cgroup *cgrp)
-{
-	int count = 0;
-	struct cgrp_cset_link *link;
-
-	spin_lock_irq(&css_set_lock);
-	list_for_each_entry(link, &cgrp->cset_links, cset_link)
-		count += link->cset->nr_tasks;
-	spin_unlock_irq(&css_set_lock);
-	return count;
-}
-
 /*
  * Load a cgroup's pidarray with either procs' tgids or tasks' pids
  */
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 4a3dae2a8283..ef3442555b32 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -561,6 +561,39 @@ static void cgroup_get_live(struct cgroup *cgrp)
 	css_get(&cgrp->self);
 }
 
+/**
+ * __cgroup_task_count - count the number of tasks in a cgroup. The caller
+ * is responsible for taking the css_set_lock.
+ * @cgrp: the cgroup in question
+ */
+int __cgroup_task_count(const struct cgroup *cgrp)
+{
+	int count = 0;
+	struct cgrp_cset_link *link;
+
+	lockdep_assert_held(&css_set_lock);
+
+	list_for_each_entry(link, &cgrp->cset_links, cset_link)
+		count += link->cset->nr_tasks;
+
+	return count;
+}
+
+/**
+ * cgroup_task_count - count the number of tasks in a cgroup.
+ * @cgrp: the cgroup in question
+ */
+int cgroup_task_count(const struct cgroup *cgrp)
+{
+	int count;
+
+	spin_lock_irq(&css_set_lock);
+	count = __cgroup_task_count(cgrp);
+	spin_unlock_irq(&css_set_lock);
+
+	return count;
+}
+
 struct cgroup_subsys_state *of_css(struct kernfs_open_file *of)
 {
 	struct cgroup *cgrp = of->kn->parent->priv;
-- 
2.17.2

[PATCH 3/5] cgroup: cgroup v2 freezer

[Roman Gushchin]

Cgroup v1 implements the freezer controller, which provides an ability
to stop the workload in a cgroup and temporarily free up some
resources (cpu, io, network bandwidth and, potentially, memory)
for some other tasks. Cgroup v2 lacks this functionality.

This patch implements freezer for cgroup v2. However the functionality
is similar, the interface is different to cgroup v1: it follows
cgroup v2 interface principles.

Key differences are:
1) There is no separate controller: the functionality is always
available and is represented by cgroup.freeze and cgroup.events
cgroup control files.
2) The desired state is defined by the cgroup.freeze control file.
Any hierarchical configuration is allowed.
3) The interface is asynchronous. The actual state is available
using cgroup.events control file ("frozen" field). There are no
dedicated transitional states.
4) It's allowed to make any changes with the cgroup hierarchy
(create new cgroups, remove old cgroups, move tasks between cgroups)
no matter if some cgroups are frozen.
5) Tasks in a frozen cgroup can be killed.

Signed-off-by: Roman Gushchin <guro@fb.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: kernel-team@fb.com
---
 include/linux/cgroup-defs.h  |  33 +++++
 include/linux/cgroup.h       |  42 ++++++
 include/linux/sched.h        |   5 +-
 include/linux/sched/jobctl.h |   5 +-
 kernel/cgroup/Makefile       |   2 +-
 kernel/cgroup/cgroup.c       |  99 +++++++++++++-
 kernel/cgroup/freezer.c      | 247 +++++++++++++++++++++++++++++++++++
 kernel/ptrace.c              |   6 +
 kernel/signal.c              |  51 ++++++--
 9 files changed, 472 insertions(+), 18 deletions(-)
 create mode 100644 kernel/cgroup/freezer.c

diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 22254c1fe1c5..600165d0f5a2 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -63,6 +63,12 @@ enum {
 	 * specified at mount time and thus is implemented here.
 	 */
 	CGRP_CPUSET_CLONE_CHILDREN,
+
+	/* Control group has to be frozen. */
+	CGRP_FREEZE,
+
+	/* Cgroup is frozen. */
+	CGRP_FROZEN,
 };
 
 /* cgroup_root->flags */
@@ -314,6 +320,27 @@ struct cgroup_rstat_cpu {
 	struct cgroup *updated_next;		/* NULL iff not on the list */
 };
 
+struct cgroup_freezer_state {
+	/* Should the cgroup actually be frozen?
+	 * (protected by cgroup_mutex)
+	 */
+	int e_freeze;
+
+	/* Fields below are protected by css_set_lock */
+
+	/* Number of frozen descendant cgroups */
+	int nr_frozen_descendants;
+
+	/* Number of tasks to freeze */
+	int nr_tasks_to_freeze;
+
+	/* Number of frozen tasks */
+	int nr_frozen_tasks;
+
+	/* Used for delayed notifications */
+	struct work_struct notify_work;
+};
+
 struct cgroup {
 	/* self css with NULL ->ss, points back to this cgroup */
 	struct cgroup_subsys_state self;
@@ -442,6 +469,12 @@ struct cgroup {
 	/* If there is block congestion on this cgroup. */
 	atomic_t congestion_count;
 
+	/* Should the cgroup and its descendants be frozen. */
+	bool freeze;
+
+	/* Used to store internal freezer state */
+	struct cgroup_freezer_state freezer;
+
 	/* ids of the ancestors at each level including self */
 	int ancestor_ids[];
 };
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 32c553556bbd..8f7e82b05bf8 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -871,4 +871,46 @@ static inline void put_cgroup_ns(struct cgroup_namespace *ns)
 		free_cgroup_ns(ns);
 }
 
+#ifdef CONFIG_CGROUPS
+
+static inline bool cgroup_frozen(struct task_struct *task)
+{
+	bool ret;
+
+	rcu_read_lock();
+	ret = test_bit(CGRP_FREEZE, &task_dfl_cgroup(task)->flags);
+	rcu_read_unlock();
+
+	return ret;
+}
+
+static inline bool cgroup_task_in_freezer(struct task_struct *task)
+{
+	return task->frozen;
+}
+
+void cgroup_freezer_enter(void);
+void cgroup_freezer_leave(void);
+void cgroup_freeze(struct cgroup *cgrp, bool freeze);
+void cgroup_notify_frozen_fn(struct work_struct *work);
+void cgroup_notify_frozen(struct cgroup *cgrp, bool frozen);
+void cgroup_queue_notify_frozen(struct cgroup *cgrp);
+void cgroup_freezer_migrate_task(struct task_struct *task, struct cgroup *src,
+				 struct cgroup *dst);
+
+#else /* !CONFIG_CGROUPS */
+
+static inline bool cgroup_task_in_freezer(struct task_struct *task)
+{
+	return false;
+}
+static inline void cgroup_freezer_enter(void) { }
+static inline void cgroup_freezer_leave(void) { }
+static inline bool cgroup_frozen(struct task_struct *task)
+{
+	return false;
+}
+
+#endif /* !CONFIG_CGROUPS */
+
 #endif /* _LINUX_CGROUP_H */
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 977cb57d7bc9..8ef5d3174e50 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -83,7 +83,8 @@ struct task_group;
 #define TASK_WAKING			0x0200
 #define TASK_NOLOAD			0x0400
 #define TASK_NEW			0x0800
-#define TASK_STATE_MAX			0x1000
+#define TASK_FROZEN			0x1000
+#define TASK_STATE_MAX			0x2000
 
 /* Convenience macros for the sake of set_current_state: */
 #define TASK_KILLABLE			(TASK_WAKEKILL | TASK_UNINTERRUPTIBLE)
@@ -733,6 +734,8 @@ struct task_struct {
 #ifdef CONFIG_CGROUPS
 	/* disallow userland-initiated cgroup migration */
 	unsigned			no_cgroup_migration:1;
+	/* task is in the cgroup freezer loop */
+	unsigned			frozen:1;
 #endif
 #ifdef CONFIG_BLK_CGROUP
 	/* to be used once the psi infrastructure lands upstream. */
diff --git a/include/linux/sched/jobctl.h b/include/linux/sched/jobctl.h
index 98228bd48aee..6c49455dcfe6 100644
--- a/include/linux/sched/jobctl.h
+++ b/include/linux/sched/jobctl.h
@@ -18,6 +18,7 @@ struct task_struct;
 #define JOBCTL_TRAP_NOTIFY_BIT	20	/* trap for NOTIFY */
 #define JOBCTL_TRAPPING_BIT	21	/* switching to TRACED */
 #define JOBCTL_LISTENING_BIT	22	/* ptracer is listening for events */
+#define JOBCTL_TRAP_FREEZE_BIT	23	/* trap for cgroup freezer */
 
 #define JOBCTL_STOP_DEQUEUED	(1UL << JOBCTL_STOP_DEQUEUED_BIT)
 #define JOBCTL_STOP_PENDING	(1UL << JOBCTL_STOP_PENDING_BIT)
@@ -26,8 +27,10 @@ struct task_struct;
 #define JOBCTL_TRAP_NOTIFY	(1UL << JOBCTL_TRAP_NOTIFY_BIT)
 #define JOBCTL_TRAPPING		(1UL << JOBCTL_TRAPPING_BIT)
 #define JOBCTL_LISTENING	(1UL << JOBCTL_LISTENING_BIT)
+#define JOBCTL_TRAP_FREEZE	(1UL << JOBCTL_TRAP_FREEZE_BIT)
 
-#define JOBCTL_TRAP_MASK	(JOBCTL_TRAP_STOP | JOBCTL_TRAP_NOTIFY)
+#define JOBCTL_TRAP_MASK	(JOBCTL_TRAP_STOP | JOBCTL_TRAP_NOTIFY | \
+				 JOBCTL_TRAP_FREEZE)
 #define JOBCTL_PENDING_MASK	(JOBCTL_STOP_PENDING | JOBCTL_TRAP_MASK)
 
 extern bool task_set_jobctl_pending(struct task_struct *task, unsigned long mask);
diff --git a/kernel/cgroup/Makefile b/kernel/cgroup/Makefile
index 8d5689ca94b9..5d7a76bfbbb7 100644
--- a/kernel/cgroup/Makefile
+++ b/kernel/cgroup/Makefile
@@ -1,5 +1,5 @@
 # SPDX-License-Identifier: GPL-2.0
-obj-y := cgroup.o rstat.o namespace.o cgroup-v1.o
+obj-y := cgroup.o rstat.o namespace.o cgroup-v1.o freezer.o
 
 obj-$(CONFIG_CGROUP_FREEZER) += legacy_freezer.o
 obj-$(CONFIG_CGROUP_PIDS) += pids.o
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index ef3442555b32..4cffaae075af 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -2358,6 +2358,10 @@ static int cgroup_migrate_execute(struct cgroup_mgctx *mgctx)
 			css_set_move_task(task, from_cset, to_cset, true);
 			put_css_set_locked(from_cset);
 			from_cset->nr_tasks--;
+
+			cgroup_freezer_migrate_task(task,
+						    from_cset->dfl_cgrp,
+						    to_cset->dfl_cgrp);
 		}
 	}
 	spin_unlock_irq(&css_set_lock);
@@ -3401,8 +3405,11 @@ static ssize_t cgroup_max_depth_write(struct kernfs_open_file *of,
 
 static int cgroup_events_show(struct seq_file *seq, void *v)
 {
-	seq_printf(seq, "populated %d\n",
-		   cgroup_is_populated(seq_css(seq)->cgroup));
+	struct cgroup *cgrp = seq_css(seq)->cgroup;
+
+	seq_printf(seq, "populated %d\n", cgroup_is_populated(cgrp));
+	seq_printf(seq, "frozen %d\n", test_bit(CGRP_FROZEN, &cgrp->flags));
+
 	return 0;
 }
 
@@ -3449,6 +3456,40 @@ static int cpu_stat_show(struct seq_file *seq, void *v)
 	return ret;
 }
 
+static int cgroup_freeze_show(struct seq_file *seq, void *v)
+{
+	struct cgroup *cgrp = seq_css(seq)->cgroup;
+
+	seq_printf(seq, "%d\n", cgrp->freeze);
+
+	return 0;
+}
+
+static ssize_t cgroup_freeze_write(struct kernfs_open_file *of,
+				   char *buf, size_t nbytes, loff_t off)
+{
+	struct cgroup *cgrp;
+	ssize_t ret;
+	int freeze;
+
+	ret = kstrtoint(strstrip(buf), 0, &freeze);
+	if (ret)
+		return ret;
+
+	if (freeze < 0 || freeze > 1)
+		return -ERANGE;
+
+	cgrp = cgroup_kn_lock_live(of->kn, false);
+	if (!cgrp)
+		return -ENOENT;
+
+	cgroup_freeze(cgrp, freeze);
+
+	cgroup_kn_unlock(of->kn);
+
+	return nbytes;
+}
+
 static int cgroup_file_open(struct kernfs_open_file *of)
 {
 	struct cftype *cft = of->kn->priv;
@@ -4574,6 +4615,12 @@ static struct cftype cgroup_base_files[] = {
 		.name = "cgroup.stat",
 		.seq_show = cgroup_stat_show,
 	},
+	{
+		.name = "cgroup.freeze",
+		.flags = CFTYPE_NOT_ON_ROOT,
+		.seq_show = cgroup_freeze_show,
+		.write = cgroup_freeze_write,
+	},
 	{
 		.name = "cpu.stat",
 		.flags = CFTYPE_NOT_ON_ROOT,
@@ -4899,11 +4946,20 @@ static struct cgroup *cgroup_create(struct cgroup *parent)
 	if (ret)
 		goto out_idr_free;
 
+	INIT_WORK(&cgrp->freezer.notify_work, cgroup_notify_frozen_fn);
+	cgrp->freezer.e_freeze = parent->freezer.e_freeze;
+	if (cgrp->freezer.e_freeze)
+		set_bit(CGRP_FROZEN, &cgrp->flags);
+
 	for (tcgrp = cgrp; tcgrp; tcgrp = cgroup_parent(tcgrp)) {
 		cgrp->ancestor_ids[tcgrp->level] = tcgrp->id;
 
-		if (tcgrp != cgrp)
+		if (tcgrp != cgrp) {
 			tcgrp->nr_descendants++;
+
+			if (cgrp->freezer.e_freeze)
+				tcgrp->freezer.nr_frozen_descendants++;
+		}
 	}
 
 	if (notify_on_release(parent))
@@ -5190,6 +5246,8 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
 	for (tcgrp = cgroup_parent(cgrp); tcgrp; tcgrp = cgroup_parent(tcgrp)) {
 		tcgrp->nr_descendants--;
 		tcgrp->nr_dying_descendants++;
+		if (cgrp->freezer.e_freeze)
+			tcgrp->freezer.nr_frozen_descendants--;
 	}
 
 	cgroup1_check_for_release(parent);
@@ -5642,6 +5700,23 @@ void cgroup_post_fork(struct task_struct *child)
 			cset->nr_tasks++;
 			css_set_move_task(child, NULL, cset, false);
 		}
+
+		if (unlikely(cgroup_frozen(child) &&
+			     (child->flags & ~PF_KTHREAD))) {
+			struct cgroup *cgrp;
+			unsigned long flags;
+
+			if (lock_task_sighand(child, &flags)) {
+				cgrp = cset->dfl_cgrp;
+				cgrp->freezer.nr_tasks_to_freeze++;
+				WARN_ON_ONCE(cgrp->freezer.nr_tasks_to_freeze <
+					     cgrp->freezer.nr_frozen_tasks);
+				child->jobctl |= JOBCTL_TRAP_FREEZE;
+				signal_wake_up(child, false);
+				unlock_task_sighand(child, &flags);
+			}
+		}
+
 		spin_unlock_irq(&css_set_lock);
 	}
 
@@ -5690,6 +5765,24 @@ void cgroup_exit(struct task_struct *tsk)
 		spin_lock_irq(&css_set_lock);
 		css_set_move_task(tsk, cset, NULL, false);
 		cset->nr_tasks--;
+
+		if (unlikely(cgroup_frozen(tsk) &&
+			     (tsk->flags & ~PF_KTHREAD))) {
+			struct cgroup *frozen_cgrp = cset->dfl_cgrp;
+
+			frozen_cgrp->freezer.nr_tasks_to_freeze--;
+
+			WARN_ON(tsk->frozen);
+			WARN_ON_ONCE(frozen_cgrp->freezer.nr_tasks_to_freeze <
+				     0);
+			WARN_ON_ONCE(frozen_cgrp->freezer.nr_tasks_to_freeze <
+				     frozen_cgrp->freezer.nr_frozen_tasks);
+
+			if (frozen_cgrp->freezer.nr_frozen_tasks ==
+			    frozen_cgrp->freezer.nr_tasks_to_freeze)
+				cgroup_queue_notify_frozen(frozen_cgrp);
+		}
+
 		spin_unlock_irq(&css_set_lock);
 	} else {
 		get_css_set(cset);
diff --git a/kernel/cgroup/freezer.c b/kernel/cgroup/freezer.c
new file mode 100644
index 000000000000..b81e215e2cce
--- /dev/null
+++ b/kernel/cgroup/freezer.c
@@ -0,0 +1,247 @@
+//SPDX-License-Identifier: GPL-2.0
+#include <linux/cgroup.h>
+#include <linux/sched.h>
+#include <linux/sched/task.h>
+#include <linux/sched/signal.h>
+
+#include "cgroup-internal.h"
+
+void cgroup_notify_frozen(struct cgroup *cgrp, bool frozen)
+{
+	int delta = 1;
+
+	lockdep_assert_held(&cgroup_mutex);
+
+	/*
+	 * Did we race with fork() or exit()? Np, everything is still frozen.
+	 */
+	if (frozen == test_bit(CGRP_FROZEN, &cgrp->flags))
+		return;
+
+	if (frozen)
+		set_bit(CGRP_FROZEN, &cgrp->flags);
+	else
+		clear_bit(CGRP_FROZEN, &cgrp->flags);
+	cgroup_file_notify(&cgrp->events_file);
+
+	while ((cgrp = cgroup_parent(cgrp))) {
+		if (frozen) {
+			cgrp->freezer.nr_frozen_descendants += delta;
+			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);
+				delta++;
+			}
+		} else {
+			cgrp->freezer.nr_frozen_descendants -= delta;
+			if (test_bit(CGRP_FROZEN, &cgrp->flags)) {
+				clear_bit(CGRP_FROZEN, &cgrp->flags);
+				cgroup_file_notify(&cgrp->events_file);
+				delta++;
+			}
+		}
+	}
+}
+
+void cgroup_notify_frozen_fn(struct work_struct *work)
+{
+	struct cgroup *cgrp = container_of(work, struct cgroup,
+					   freezer.notify_work);
+
+	mutex_lock(&cgroup_mutex);
+	cgroup_notify_frozen(cgrp, true);
+	mutex_unlock(&cgroup_mutex);
+
+	css_put(&cgrp->self);
+}
+
+void cgroup_queue_notify_frozen(struct cgroup *cgrp)
+{
+	if (work_pending(&cgrp->freezer.notify_work))
+		return;
+
+	css_get(&cgrp->self);
+	schedule_work(&cgrp->freezer.notify_work);
+}
+
+void cgroup_freezer_enter(void)
+{
+	long state = current->state;
+	struct cgroup *cgrp;
+
+	if (!current->frozen) {
+		spin_lock_irq(&css_set_lock);
+		current->frozen = true;
+		cgrp = task_dfl_cgroup(current);
+		cgrp->freezer.nr_frozen_tasks++;
+
+		WARN_ON_ONCE(cgrp->freezer.nr_tasks_to_freeze <
+			     cgrp->freezer.nr_frozen_tasks);
+
+		if (cgrp->freezer.nr_tasks_to_freeze ==
+		    cgrp->freezer.nr_frozen_tasks)
+			cgroup_queue_notify_frozen(cgrp);
+		spin_unlock_irq(&css_set_lock);
+	}
+
+	/* refrigerator */
+	set_current_state(TASK_WAKEKILL | TASK_INTERRUPTIBLE | TASK_FROZEN);
+	clear_thread_flag(TIF_SIGPENDING);
+	schedule();
+	recalc_sigpending();
+
+	set_current_state(state);
+}
+
+void cgroup_freezer_leave(void)
+{
+	struct cgroup *cgrp;
+
+	spin_lock_irq(&css_set_lock);
+	cgrp = task_dfl_cgroup(current);
+	cgrp->freezer.nr_frozen_tasks--;
+	WARN_ON_ONCE(cgrp->freezer.nr_frozen_tasks < 0);
+	current->frozen = false;
+	spin_unlock_irq(&css_set_lock);
+}
+
+static void cgroup_do_freeze(struct cgroup *cgrp, bool freeze)
+{
+	struct css_task_iter it;
+	struct task_struct *task;
+	unsigned long flags;
+
+	lockdep_assert_held(&cgroup_mutex);
+
+	spin_lock_irq(&css_set_lock);
+	if (freeze) {
+		cgrp->freezer.nr_tasks_to_freeze = __cgroup_task_count(cgrp);
+		set_bit(CGRP_FREEZE, &cgrp->flags);
+	} else {
+		clear_bit(CGRP_FREEZE, &cgrp->flags);
+		cgroup_notify_frozen(cgrp, false);
+	}
+	spin_unlock_irq(&css_set_lock);
+
+	css_task_iter_start(&cgrp->self, 0, &it);
+	while ((task = css_task_iter_next(&it))) {
+		if (task->flags & PF_KTHREAD)
+			continue;
+
+		if (!lock_task_sighand(task, &flags))
+			continue;
+
+		if (freeze) {
+			task->jobctl |= JOBCTL_TRAP_FREEZE;
+			signal_wake_up(task, false);
+		} else {
+			task->jobctl &= ~JOBCTL_TRAP_FREEZE;
+			wake_up_process(task);
+		}
+
+		unlock_task_sighand(task, &flags);
+	}
+	css_task_iter_end(&it);
+
+	if (freeze && cgrp->nr_descendants ==
+	    cgrp->freezer.nr_frozen_descendants) {
+		spin_lock_irq(&css_set_lock);
+		WARN_ON_ONCE(cgrp->freezer.nr_tasks_to_freeze <
+			     cgrp->freezer.nr_frozen_tasks);
+		if (cgrp->freezer.nr_tasks_to_freeze ==
+		    cgrp->freezer.nr_frozen_tasks)
+			cgroup_notify_frozen(cgrp, true);
+		spin_unlock_irq(&css_set_lock);
+	}
+}
+
+void cgroup_freezer_migrate_task(struct task_struct *task,
+				 struct cgroup *src, struct cgroup *dst)
+{
+	unsigned long flags;
+
+	lockdep_assert_held(&css_set_lock);
+
+	if (task->flags & PF_KTHREAD)
+		return;
+
+	if (test_bit(CGRP_FREEZE, &src->flags) || task->frozen)
+		src->freezer.nr_tasks_to_freeze--;
+	if (test_bit(CGRP_FREEZE, &dst->flags) || task->frozen)
+		dst->freezer.nr_tasks_to_freeze++;
+
+	if (task->frozen) {
+		src->freezer.nr_frozen_tasks--;
+		dst->freezer.nr_frozen_tasks++;
+	}
+
+	if (test_bit(CGRP_FREEZE, &src->flags) ==
+	    test_bit(CGRP_FREEZE, &dst->flags))
+		return;
+
+	if (lock_task_sighand(task, &flags)) {
+		if (test_bit(CGRP_FREEZE, &dst->flags))
+			task->jobctl |= JOBCTL_TRAP_FREEZE;
+		else
+			task->jobctl &= ~JOBCTL_TRAP_FREEZE;
+		signal_wake_up(task, false);
+		unlock_task_sighand(task, &flags);
+	}
+}
+
+void cgroup_freeze(struct cgroup *cgrp, bool freeze)
+{
+	struct cgroup_subsys_state *css;
+	struct cgroup *dsct;
+	bool applied = false;
+
+	lockdep_assert_held(&cgroup_mutex);
+
+	/*
+	 * Nothing changed? Just exit.
+	 */
+	if (cgrp->freeze == freeze)
+		return;
+
+	cgrp->freeze = freeze;
+
+	/*
+	 * Propagate changes downwards the cgroup tree.
+	 */
+	css_for_each_descendant_pre(css, &cgrp->self) {
+		dsct = css->cgroup;
+
+		if (cgroup_is_dead(dsct))
+			continue;
+
+		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;
+
+			WARN_ON_ONCE(dsct->freezer.e_freeze < 0);
+		}
+
+		/*
+		 * Do change actual state: freeze or unfreeze.
+		 */
+		cgroup_do_freeze(dsct, freeze);
+		applied = true;
+	}
+
+	if (!applied)
+		cgroup_file_notify(&cgrp->events_file);
+}
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 21fec73d45d4..5e484e2480e5 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -400,6 +400,12 @@ static int ptrace_attach(struct task_struct *task, long request,
 
 	spin_lock(&task->sighand->siglock);
 
+	/*
+	 * Kick the process to get it out of the refrigerator.
+	 */
+	if (cgroup_frozen(task))
+		wake_up_process(task);
+
 	/*
 	 * If the task is already STOPPED, set JOBCTL_TRAP_STOP and
 	 * TRAPPING, and kick it so that it transits to TRACED.  TRAPPING
diff --git a/kernel/signal.c b/kernel/signal.c
index 5843c541fda9..41fee9a38201 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -326,6 +326,11 @@ void task_clear_jobctl_pending(struct task_struct *task, unsigned long mask)
 	if (mask & JOBCTL_STOP_PENDING)
 		mask |= JOBCTL_STOP_CONSUME | JOBCTL_STOP_DEQUEUED;
 
+	/*
+	 * JOBCTL_TRAP_FREEZE is set and cleared from cgroup side,
+	 * don't touch it here.
+	 */
+	mask &= ~JOBCTL_TRAP_FREEZE;
 	task->jobctl &= ~mask;
 
 	if (!(task->jobctl & JOBCTL_PENDING_MASK))
@@ -2252,7 +2257,7 @@ static bool do_signal_stop(int signr)
 }
 
 /**
- * do_jobctl_trap - take care of ptrace jobctl traps
+ * do_jobctl_trap - take care of ptrace and cgroup freezer jobctl traps
  *
  * When PT_SEIZED, it's used for both group stop and explicit
  * SEIZE/INTERRUPT traps.  Both generate PTRACE_EVENT_STOP trap with
@@ -2268,20 +2273,35 @@ static bool do_signal_stop(int signr)
  */
 static void do_jobctl_trap(void)
 {
+	struct sighand_struct *sighand = current->sighand;
 	struct signal_struct *signal = current->signal;
 	int signr = current->jobctl & JOBCTL_STOP_SIGMASK;
 
-	if (current->ptrace & PT_SEIZED) {
-		if (!signal->group_stop_count &&
-		    !(signal->flags & SIGNAL_STOP_STOPPED))
-			signr = SIGTRAP;
-		WARN_ON_ONCE(!signr);
-		ptrace_do_notify(signr, signr | (PTRACE_EVENT_STOP << 8),
-				 CLD_STOPPED);
-	} else {
-		WARN_ON_ONCE(!signr);
-		ptrace_stop(signr, CLD_STOPPED, 0, NULL);
-		current->exit_code = 0;
+	if (current->jobctl & (JOBCTL_TRAP_STOP | JOBCTL_TRAP_NOTIFY)) {
+		if (current->ptrace & PT_SEIZED) {
+			if (!signal->group_stop_count &&
+			    !(signal->flags & SIGNAL_STOP_STOPPED))
+				signr = SIGTRAP;
+			WARN_ON_ONCE(!signr);
+			ptrace_do_notify(signr,
+					 signr | (PTRACE_EVENT_STOP << 8),
+					 CLD_STOPPED);
+		} else {
+			WARN_ON_ONCE(!signr);
+			ptrace_stop(signr, CLD_STOPPED, 0, NULL);
+			current->exit_code = 0;
+		}
+	} else if (current->jobctl & JOBCTL_TRAP_FREEZE) {
+		/*
+		 * Enter the freezer, unless the task is about to exit.
+		 */
+		if (fatal_signal_pending(current)) {
+			current->jobctl &= ~JOBCTL_TRAP_FREEZE;
+		} else {
+			spin_unlock_irq(&sighand->siglock);
+			cgroup_freezer_enter();
+			spin_lock_irq(&sighand->siglock);
+		}
 	}
 }
 
@@ -2403,6 +2423,13 @@ bool get_signal(struct ksignal *ksig)
 			goto relock;
 		}
 
+		/*
+		 * If the task is leaving the freezer look, let's notify
+		 * the cgroup and reset the frozen mark.
+		 */
+		if (unlikely(cgroup_task_in_freezer(current)))
+			cgroup_freezer_leave();
+
 		signr = dequeue_signal(current, &current->blocked, &ksig->info);
 
 		if (!signr)
-- 
2.17.2

[PATCH 4/5] kselftests: cgroup: don't fail on cg_kill_all() error in cg_destroy()

[Roman Gushchin]

If the cgroup destruction races with an exit() of a belonging
process(es), cg_kill_all() may fail. It's not a good reason to make
cg_destroy() fail and leave the cgroup in place, potentially causing
next test runs to fail.

Signed-off-by: Roman Gushchin <guro@fb.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: kernel-team@fb.com
---
 tools/testing/selftests/cgroup/cgroup_util.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/tools/testing/selftests/cgroup/cgroup_util.c b/tools/testing/selftests/cgroup/cgroup_util.c
index 14c9fe284806..eba06f94433b 100644
--- a/tools/testing/selftests/cgroup/cgroup_util.c
+++ b/tools/testing/selftests/cgroup/cgroup_util.c
@@ -227,9 +227,7 @@ int cg_destroy(const char *cgroup)
 retry:
 	ret = rmdir(cgroup);
 	if (ret && errno == EBUSY) {
-		ret = cg_killall(cgroup);
-		if (ret)
-			return ret;
+		cg_killall(cgroup);
 		usleep(100);
 		goto retry;
 	}
-- 
2.17.2

[PATCH 5/5] kselftests: cgroup: add freezer controller self-tests

[Roman Gushchin]

This patch implements six tests for the freezer controller for
cgroup v2:
1) a simple test, which aims to freeze and unfreeze a cgroup with 100
processes
2) a more complicated tree test, which creates a hierarchy of cgroups,
puts some processes in some cgroups, and tries to freeze and unfreeze
different parts of the subtree
3) a forkbomb test: the test aims to freeze a forkbomb running in a
cgroup, kill all tasks in the cgroup and remove the cgroup without
the unfreezing.
4) rmdir test: the test creates two nested cgroups, freezes the parent
one, checks that the child can be successfully removed, and a new
child can be created
5) migration tests: the test checks migration of a task between
frozen cgroups: from a frozen to a running, from a running to a
frozen, and from a frozen to a frozen.
6) ptrace test: the test checks that it's possible to attach to
a process in a frozen cgroup, get some information and detach, and
the cgroup will remain frozen.

Expected output:

  $ ./test_freezer
  ok 1 test_cgfreezer_simple
  ok 2 test_cgfreezer_tree
  ok 3 test_cgfreezer_forkbomb
  ok 4 test_cgrreezer_rmdir
  ok 5 test_cgfreezer_migrate
  ok 6 test_cgfreezer_ptrace

Signed-off-by: Roman Gushchin <guro@fb.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: kernel-team@fb.com
---
 tools/testing/selftests/cgroup/.gitignore     |   1 +
 tools/testing/selftests/cgroup/Makefile       |   2 +
 tools/testing/selftests/cgroup/cgroup_util.c  |  81 ++-
 tools/testing/selftests/cgroup/cgroup_util.h  |   7 +
 tools/testing/selftests/cgroup/test_freezer.c | 685 ++++++++++++++++++
 5 files changed, 775 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/cgroup/test_freezer.c

diff --git a/tools/testing/selftests/cgroup/.gitignore b/tools/testing/selftests/cgroup/.gitignore
index adacda50a4b2..7f9835624793 100644
--- a/tools/testing/selftests/cgroup/.gitignore
+++ b/tools/testing/selftests/cgroup/.gitignore
@@ -1,2 +1,3 @@
 test_memcontrol
 test_core
+test_freezer
diff --git a/tools/testing/selftests/cgroup/Makefile b/tools/testing/selftests/cgroup/Makefile
index 23fbaa4a9630..8d369b6a2069 100644
--- a/tools/testing/selftests/cgroup/Makefile
+++ b/tools/testing/selftests/cgroup/Makefile
@@ -5,8 +5,10 @@ all:
 
 TEST_GEN_PROGS = test_memcontrol
 TEST_GEN_PROGS += test_core
+TEST_GEN_PROGS += test_freezer
 
 include ../lib.mk
 
 $(OUTPUT)/test_memcontrol: cgroup_util.c
 $(OUTPUT)/test_core: cgroup_util.c
+$(OUTPUT)/test_freezer: cgroup_util.c
diff --git a/tools/testing/selftests/cgroup/cgroup_util.c b/tools/testing/selftests/cgroup/cgroup_util.c
index eba06f94433b..e9cdad673901 100644
--- a/tools/testing/selftests/cgroup/cgroup_util.c
+++ b/tools/testing/selftests/cgroup/cgroup_util.c
@@ -74,6 +74,16 @@ char *cg_name_indexed(const char *root, const char *name, int index)
 	return ret;
 }
 
+char *cg_control(const char *cgroup, const char *control)
+{
+	size_t len = strlen(cgroup) + strlen(control) + 2;
+	char *ret = malloc(len);
+
+	snprintf(ret, len, "%s/%s", cgroup, control);
+
+	return ret;
+}
+
 int cg_read(const char *cgroup, const char *control, char *buf, size_t len)
 {
 	char path[PATH_MAX];
@@ -196,7 +206,59 @@ int cg_create(const char *cgroup)
 	return mkdir(cgroup, 0644);
 }
 
-static int cg_killall(const char *cgroup)
+int cg_for_all_procs(const char *cgroup, int (*fn)(int pid, void *arg),
+		     void *arg)
+{
+	char buf[PAGE_SIZE];
+	char *ptr = buf;
+	int ret;
+
+	if (cg_read(cgroup, "cgroup.procs", buf, sizeof(buf)))
+		return -1;
+
+	while (ptr < buf + sizeof(buf)) {
+		int pid = strtol(ptr, &ptr, 10);
+
+		if (pid == 0)
+			break;
+		if (*ptr)
+			ptr++;
+		else
+			break;
+		ret = fn(pid, arg);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
+int cg_wait_for_proc_count(const char *cgroup, int count)
+{
+	char buf[10 * PAGE_SIZE] = {0};
+	int attempts;
+	char *ptr;
+
+	for (attempts = 10; attempts >= 0; attempts--) {
+		int nr = 0;
+
+		if (cg_read(cgroup, "cgroup.procs", buf, sizeof(buf)))
+			break;
+
+		for (ptr = buf; *ptr; ptr++)
+			if (*ptr == '\n')
+				nr++;
+
+		if (nr >= count)
+			return 0;
+
+		usleep(100000);
+	}
+
+	return -1;
+}
+
+int cg_killall(const char *cgroup)
 {
 	char buf[PAGE_SIZE];
 	char *ptr = buf;
@@ -238,6 +300,14 @@ int cg_destroy(const char *cgroup)
 	return ret;
 }
 
+int cg_enter(const char *cgroup, int pid)
+{
+	char pidbuf[64];
+
+	snprintf(pidbuf, sizeof(pidbuf), "%d", pid);
+	return cg_write(cgroup, "cgroup.procs", pidbuf);
+}
+
 int cg_enter_current(const char *cgroup)
 {
 	char pidbuf[64];
@@ -367,3 +437,12 @@ int set_oom_adj_score(int pid, int score)
 	close(fd);
 	return 0;
 }
+
+char proc_read_text(int pid, const char *item, char *buf, size_t size)
+{
+	char path[PATH_MAX];
+
+	snprintf(path, sizeof(path), "/proc/%d/%s", pid, item);
+
+	return read_text(path, buf, size);
+}
diff --git a/tools/testing/selftests/cgroup/cgroup_util.h b/tools/testing/selftests/cgroup/cgroup_util.h
index 9ac8b7958f83..8ee63c00a668 100644
--- a/tools/testing/selftests/cgroup/cgroup_util.h
+++ b/tools/testing/selftests/cgroup/cgroup_util.h
@@ -18,6 +18,7 @@ static inline int values_close(long a, long b, int err)
 extern int cg_find_unified_root(char *root, size_t len);
 extern char *cg_name(const char *root, const char *name);
 extern char *cg_name_indexed(const char *root, const char *name, int index);
+extern char *cg_control(const char *cgroup, const char *control);
 extern int cg_create(const char *cgroup);
 extern int cg_destroy(const char *cgroup);
 extern int cg_read(const char *cgroup, const char *control,
@@ -32,6 +33,7 @@ extern int cg_write(const char *cgroup, const char *control, char *buf);
 extern int cg_run(const char *cgroup,
 		  int (*fn)(const char *cgroup, void *arg),
 		  void *arg);
+extern int cg_enter(const char *cgroup, int pid);
 extern int cg_enter_current(const char *cgroup);
 extern int cg_run_nowait(const char *cgroup,
 			 int (*fn)(const char *cgroup, void *arg),
@@ -41,3 +43,8 @@ extern int alloc_pagecache(int fd, size_t size);
 extern int alloc_anon(const char *cgroup, void *arg);
 extern int is_swap_enabled(void);
 extern int set_oom_adj_score(int pid, int score);
+extern int cg_for_all_procs(const char *cgroup, int (*fn)(int pid, void *arg),
+			    void *arg);
+extern int cg_wait_for_proc_count(const char *cgroup, int count);
+extern int cg_killall(const char *cgroup);
+extern char proc_read_text(int pid, const char *item, char *buf, size_t size);
diff --git a/tools/testing/selftests/cgroup/test_freezer.c b/tools/testing/selftests/cgroup/test_freezer.c
new file mode 100644
index 000000000000..dc9830986f08
--- /dev/null
+++ b/tools/testing/selftests/cgroup/test_freezer.c
@@ -0,0 +1,685 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#include <stdbool.h>
+#include <linux/limits.h>
+#include <sys/ptrace.h>
+#include <sys/types.h>
+#include <sys/mman.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <errno.h>
+#include <poll.h>
+#include <stdlib.h>
+#include <sys/inotify.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+
+#include "../kselftest.h"
+#include "cgroup_util.h"
+
+#define DEBUG
+#ifdef DEBUG
+#define debug(args...) fprintf(stderr, args)
+#else
+#define debug(args...)
+#endif
+
+/*
+ * Freeze the given cgroup and wait for the inotify signal.
+ * If there is no signal in 10 seconds, treat this as an error.
+ */
+static int cg_freeze_wait(const char *cgroup, bool freeze)
+{
+	int fd, wd;
+	struct pollfd fds;
+	int ret = -1;
+
+	fd = inotify_init1(IN_NONBLOCK);
+	if (fd == -1)
+		return fd;
+
+	wd = inotify_add_watch(fd, cg_control(cgroup, "cgroup.events"),
+			       IN_MODIFY);
+	if (wd == -1) {
+		close(fd);
+		return wd;
+	}
+	fds.fd = fd;
+	fds.events = POLLIN;
+
+	ret = cg_write(cgroup, "cgroup.freeze", freeze ? "1" : "0");
+	if (ret) {
+		close(fd);
+		return ret;
+	}
+
+	while (true) {
+		wd = poll(&fds, 1, 10000);
+
+		if (wd == -1 && errno == EINTR)
+			continue;
+
+		if (wd == 1 && fds.revents & POLLIN)
+			ret = 0;
+
+		break;
+	}
+
+	close(fd);
+
+	return ret;
+}
+
+/*
+ * Check if the process is frozen and parked in a proper place.
+ */
+static int proc_check_frozen(int pid, void *arg)
+{
+	char buf[PAGE_SIZE];
+	int len;
+
+	len = proc_read_text(pid, "stat", buf, sizeof(buf));
+	if (len == -1) {
+		debug("Can't get %d stat\n", pid);
+		return -1;
+	}
+
+	if (strstr(buf, "(test_freezer) S ") == NULL) {
+		debug("Process %d in the unexpected state: %s\n", pid, buf);
+		return -1;
+	}
+
+	len = proc_read_text(pid, "stack", buf, sizeof(buf));
+	if (len == -1) {
+		debug("Can't get stack of the process %d\n", pid);
+		return -1;
+	}
+
+	if (strstr(buf, "[<0>] cgroup_freezer") != buf) {
+		debug("Process %d has unexpected stacktrace: %s\n", pid, buf);
+		return -1;
+	}
+
+	return 0;
+}
+
+/*
+ * Check if the cgroup is frozen and all belonging processes are
+ * parked in a proper place.
+ */
+static int cg_check_frozen(const char *cgroup, bool frozen)
+{
+	if (frozen) {
+		/*
+		 * Check the cgroup.events::frozen value.
+		 */
+		if (cg_read_strstr(cgroup, "cgroup.events", "frozen 1") != 0) {
+			debug("Cgroup %s isn't unexpectedly frozen\n", cgroup);
+			return -1;
+		}
+
+		/*
+		 * Check that all processes are parked in the proper place.
+		 */
+		if (cg_for_all_procs(cgroup, proc_check_frozen, NULL)) {
+			debug("Some processes of cgroup %s are not frozen\n",
+			      cgroup);
+			return -1;
+		}
+	} else {
+		/*
+		 * Check the cgroup.events::frozen value.
+		 */
+		if (cg_read_strstr(cgroup, "cgroup.events", "frozen 0") != 0) {
+			debug("Cgroup %s is unexpectedly frozen\n", cgroup);
+			return -1;
+		}
+	}
+
+	return 0;
+}
+
+/*
+ * A simple process running in a sleep loop until being
+ * re-parented.
+ */
+static int child_fn(const char *cgroup, void *arg)
+{
+	int ppid = getppid();
+
+	while (getppid() == ppid)
+		usleep(1000);
+
+	return getppid() == ppid;
+}
+
+/*
+ * A simple test for the cgroup freezer: populated the cgroup with 100
+ * running processes and freeze it. Then unfreeze it. Then it kills all
+ * processes and destroys the cgroup.
+ */
+static int test_cgfreezer_simple(const char *root)
+{
+	int ret = KSFT_FAIL;
+	char *cgroup = NULL;
+	int i;
+
+	cgroup = cg_name(root, "cg_test");
+	if (!cgroup)
+		goto cleanup;
+
+	if (cg_create(cgroup))
+		goto cleanup;
+
+	for (i = 0; i < 100; i++)
+		cg_run_nowait(cgroup, child_fn, NULL);
+
+	if (cg_wait_for_proc_count(cgroup, 100))
+		goto cleanup;
+
+	if (cg_check_frozen(cgroup, false))
+		goto cleanup;
+
+	if (cg_freeze_wait(cgroup, true))
+		goto cleanup;
+
+	if (cg_check_frozen(cgroup, true))
+		goto cleanup;
+
+	if (cg_freeze_wait(cgroup, false))
+		goto cleanup;
+
+	if (cg_check_frozen(cgroup, false))
+		goto cleanup;
+
+	ret = KSFT_PASS;
+
+cleanup:
+	if (cgroup)
+		cg_destroy(cgroup);
+	free(cgroup);
+	return ret;
+}
+
+/*
+ * The test creates the following hierarchy:
+ *       A
+ *    / / \ \
+ *   B  E  I K
+ *  /\  |
+ * C  D F
+ *      |
+ *      G
+ *      |
+ *      H
+ *
+ * with a process in C, H and 3 processes in K.
+ * Then it tries to freeze and unfreeze the whole tree.
+ */
+static int test_cgfreezer_tree(const char *root)
+{
+	char *cgroup[10] = {0};
+	int ret = KSFT_FAIL;
+	int i;
+
+	cgroup[0] = cg_name(root, "cg_test_A");
+	if (!cgroup[0])
+		goto cleanup;
+
+	cgroup[1] = cg_name(cgroup[0], "cg_test_B");
+	if (!cgroup[1])
+		goto cleanup;
+
+	cgroup[2] = cg_name(cgroup[1], "cg_test_C");
+	if (!cgroup[2])
+		goto cleanup;
+
+	cgroup[3] = cg_name(cgroup[1], "cg_test_D");
+	if (!cgroup[3])
+		goto cleanup;
+
+	cgroup[4] = cg_name(cgroup[0], "cg_test_E");
+	if (!cgroup[4])
+		goto cleanup;
+
+	cgroup[5] = cg_name(cgroup[4], "cg_test_F");
+	if (!cgroup[5])
+		goto cleanup;
+
+	cgroup[6] = cg_name(cgroup[5], "cg_test_G");
+	if (!cgroup[6])
+		goto cleanup;
+
+	cgroup[7] = cg_name(cgroup[6], "cg_test_H");
+	if (!cgroup[7])
+		goto cleanup;
+
+	cgroup[8] = cg_name(cgroup[0], "cg_test_I");
+	if (!cgroup[8])
+		goto cleanup;
+
+	cgroup[9] = cg_name(cgroup[0], "cg_test_K");
+	if (!cgroup[9])
+		goto cleanup;
+
+	for (i = 0; i < 10; i++)
+		if (cg_create(cgroup[i]))
+			goto cleanup;
+
+	cg_run_nowait(cgroup[2], child_fn, NULL);
+	cg_run_nowait(cgroup[7], child_fn, NULL);
+	cg_run_nowait(cgroup[9], child_fn, NULL);
+	cg_run_nowait(cgroup[9], child_fn, NULL);
+	cg_run_nowait(cgroup[9], child_fn, NULL);
+
+	/*
+	 * Wait until all child processes will enter
+	 * corresponding cgroups.
+	 */
+
+	if (cg_wait_for_proc_count(cgroup[2], 1) ||
+	    cg_wait_for_proc_count(cgroup[7], 1) ||
+	    cg_wait_for_proc_count(cgroup[9], 3))
+		goto cleanup;
+
+	/*
+	 * Freeze B.
+	 */
+	if (cg_freeze_wait(cgroup[1], true))
+		goto cleanup;
+
+	if (cg_check_frozen(cgroup[1], true))
+		goto cleanup;
+
+	/*
+	 * Freeze F.
+	 */
+	if (cg_freeze_wait(cgroup[5], true))
+		goto cleanup;
+
+	if (cg_check_frozen(cgroup[5], true))
+		goto cleanup;
+
+	/*
+	 * Freeze G.
+	 */
+	if (cg_freeze_wait(cgroup[6], true))
+		goto cleanup;
+
+	if (cg_check_frozen(cgroup[6], true))
+		goto cleanup;
+
+	/*
+	 * Check that A and E are not frozen.
+	 */
+	if (cg_check_frozen(cgroup[0], false))
+		goto cleanup;
+
+	if (cg_check_frozen(cgroup[4], false))
+		goto cleanup;
+
+	/*
+	 * Freeze A. Check that A, B and E are frozen.
+	 */
+	if (cg_freeze_wait(cgroup[0], true))
+		goto cleanup;
+
+	if (cg_check_frozen(cgroup[0], true))
+		goto cleanup;
+
+	if (cg_check_frozen(cgroup[1], true))
+		goto cleanup;
+
+	if (cg_check_frozen(cgroup[4], true))
+		goto cleanup;
+
+	/*
+	 * Unfreeze B, F and G
+	 */
+	if (cg_freeze_wait(cgroup[1], false))
+		goto cleanup;
+
+	if (cg_freeze_wait(cgroup[5], false))
+		goto cleanup;
+
+	if (cg_freeze_wait(cgroup[6], false))
+		goto cleanup;
+
+	/*
+	 * Check that C and H are still frozen.
+	 */
+	if (cg_check_frozen(cgroup[2], true))
+		goto cleanup;
+
+	if (cg_check_frozen(cgroup[7], true))
+		goto cleanup;
+
+	/*
+	 * Unfreezing A failed. Check that A, C and K are not frozen.
+	 */
+	if (cg_freeze_wait(cgroup[0], false))
+		goto cleanup;
+
+	if (cg_check_frozen(cgroup[0], false))
+		goto cleanup;
+
+	if (cg_check_frozen(cgroup[2], false))
+		goto cleanup;
+
+	if (cg_check_frozen(cgroup[9], false))
+		goto cleanup;
+
+	ret = KSFT_PASS;
+
+cleanup:
+	for (i = 9; i >= 0 && cgroup[i]; i--) {
+		cg_destroy(cgroup[i]);
+		free(cgroup[i]);
+	}
+
+	return ret;
+}
+
+/*
+ * A fork bomb emulator.
+ */
+static int forkbomb_fn(const char *cgroup, void *arg)
+{
+	int ppid;
+
+	fork();
+	fork();
+
+	ppid = getppid();
+
+	while (getppid() == ppid)
+		usleep(1000);
+
+	return getppid() == ppid;
+}
+
+/*
+ * The test runs a fork bomb in a cgroup and tries to freeze it.
+ * Then it kills all processes and checks that cgroup isn't populated
+ * anymore.
+ */
+static int test_cgfreezer_forkbomb(const char *root)
+{
+	int ret = KSFT_FAIL;
+	char *cgroup = NULL;
+
+	cgroup = cg_name(root, "cg_forkbomb_test");
+	if (!cgroup)
+		goto cleanup;
+
+	if (cg_create(cgroup))
+		goto cleanup;
+
+	cg_run_nowait(cgroup, forkbomb_fn, NULL);
+
+	usleep(100000);
+
+	if (cg_freeze_wait(cgroup, true))
+		goto cleanup;
+
+	if (cg_check_frozen(cgroup, true))
+		goto cleanup;
+
+	if (cg_killall(cgroup))
+		goto cleanup;
+
+	if (cg_wait_for_proc_count(cgroup, 0))
+		goto cleanup;
+
+	ret = KSFT_PASS;
+
+cleanup:
+	if (cgroup)
+		cg_destroy(cgroup);
+	free(cgroup);
+	return ret;
+}
+
+/*
+ * The test creates two nested cgroups, freezes the parent
+ * and removes the child. Then it checks that the parent cgroup
+ * remains frozen and it's possible to create a new child
+ * without unfreezing. The new child is frozen too.
+ */
+static int test_cgfreezer_rmdir(const char *root)
+{
+	int ret = KSFT_FAIL;
+	char *parent, *child = NULL;
+
+	parent = cg_name(root, "cg_test_A");
+	if (!parent)
+		goto cleanup;
+
+	child = cg_name(parent, "cg_test_B");
+	if (!child)
+		goto cleanup;
+
+	if (cg_create(parent))
+		goto cleanup;
+
+	if (cg_create(child))
+		goto cleanup;
+
+	if (cg_freeze_wait(parent, true))
+		goto cleanup;
+
+	if (cg_check_frozen(parent, true))
+		goto cleanup;
+
+	if (cg_destroy(child))
+		goto cleanup;
+
+	if (cg_check_frozen(parent, true))
+		goto cleanup;
+
+	if (cg_create(child))
+		goto cleanup;
+
+	if (cg_check_frozen(child, true))
+		goto cleanup;
+
+	ret = KSFT_PASS;
+
+cleanup:
+	if (child)
+		cg_destroy(child);
+	free(child);
+	if (parent)
+		cg_destroy(parent);
+	free(parent);
+	return ret;
+}
+
+/*
+ * The test creates two cgroups: A and B. The it runs a process in A,
+ * and performs several migrations:
+ * 1) A (running) -> B (frozen)
+ * 2) B (frozen) -> A (running)
+ * 3) A (frozen) -> B (frozen)
+ *
+ * One each step it checks that the actual state of cgroups matches
+ * the expected state.
+ */
+static int test_cgfreezer_migrate(const char *root)
+{
+	int ret = KSFT_FAIL;
+	char *cgroup[2] = {0};
+	int pid;
+
+	cgroup[0] = cg_name(root, "cg_test_A");
+	if (!cgroup[0])
+		goto cleanup;
+
+	cgroup[1] = cg_name(root, "cg_test_B");
+	if (!cgroup[1])
+		goto cleanup;
+
+	if (cg_create(cgroup[0]))
+		goto cleanup;
+
+	if (cg_create(cgroup[1]))
+		goto cleanup;
+
+	pid = cg_run_nowait(cgroup[0], child_fn, NULL);
+	if (pid < 0)
+		goto cleanup;
+
+	if (cg_wait_for_proc_count(cgroup[0], 1))
+		goto cleanup;
+
+	/*
+	 * Migrate from A (running) to B (frozen)
+	 */
+	if (cg_freeze_wait(cgroup[1], true))
+		goto cleanup;
+
+	if (cg_check_frozen(cgroup[1], true))
+		goto cleanup;
+
+	if (cg_enter(cgroup[1], pid))
+		goto cleanup;
+
+	if (cg_check_frozen(cgroup[0], false))
+		goto cleanup;
+
+	if (cg_check_frozen(cgroup[1], true))
+		goto cleanup;
+
+	/*
+	 * Migrate from B (frozen) to A (running)
+	 */
+	if (cg_enter(cgroup[0], pid))
+		goto cleanup;
+
+	if (cg_check_frozen(cgroup[0], false))
+		goto cleanup;
+
+	if (cg_check_frozen(cgroup[1], true))
+		goto cleanup;
+
+	/*
+	 * Migrate from A (frozen) to B (frozen)
+	 */
+	if (cg_freeze_wait(cgroup[0], true))
+		goto cleanup;
+
+	if (cg_check_frozen(cgroup[0], true))
+		goto cleanup;
+
+	if (cg_enter(cgroup[1], pid))
+		goto cleanup;
+
+	if (cg_check_frozen(cgroup[0], true))
+		goto cleanup;
+
+	if (cg_check_frozen(cgroup[1], true))
+		goto cleanup;
+
+	ret = KSFT_PASS;
+
+cleanup:
+	if (cgroup[0])
+		cg_destroy(cgroup[0]);
+	free(cgroup[0]);
+	if (cgroup[1])
+		cg_destroy(cgroup[1]);
+	free(cgroup[1]);
+	return ret;
+}
+
+/*
+ * The test checks that ptrace works with a tracing process in a frozen cgroup.
+ */
+static int test_cgfreezer_ptrace(const char *root)
+{
+	int ret = KSFT_FAIL;
+	char *cgroup = NULL;
+	siginfo_t siginfo;
+	int pid;
+
+	cgroup = cg_name(root, "cg_test");
+	if (!cgroup)
+		goto cleanup;
+
+	if (cg_create(cgroup))
+		goto cleanup;
+
+	pid = cg_run_nowait(cgroup, child_fn, NULL);
+	if (pid < 0)
+		goto cleanup;
+
+	if (cg_wait_for_proc_count(cgroup, 1))
+		goto cleanup;
+
+	if (cg_freeze_wait(cgroup, true))
+		goto cleanup;
+
+	if (cg_check_frozen(cgroup, true))
+		goto cleanup;
+
+	if (ptrace(PTRACE_SEIZE, pid, NULL, NULL))
+		goto cleanup;
+
+	if (ptrace(PTRACE_INTERRUPT, pid, NULL, NULL))
+		goto cleanup;
+
+	waitpid(pid, NULL, 0);
+
+	if (ptrace(PTRACE_GETSIGINFO, pid, NULL, &siginfo))
+		goto cleanup;
+
+	if (ptrace(PTRACE_DETACH, pid, NULL, NULL))
+		goto cleanup;
+
+	ret = KSFT_PASS;
+
+cleanup:
+	if (cgroup)
+		cg_destroy(cgroup);
+	free(cgroup);
+	return ret;
+}
+
+#define T(x) { x, #x }
+struct cgfreezer_test {
+	int (*fn)(const char *root);
+	const char *name;
+} tests[] = {
+	T(test_cgfreezer_simple),
+	T(test_cgfreezer_tree),
+	T(test_cgfreezer_forkbomb),
+	T(test_cgfreezer_rmdir),
+	T(test_cgfreezer_migrate),
+	T(test_cgfreezer_ptrace),
+};
+#undef T
+
+int main(int argc, char *argv[])
+{
+	char root[PATH_MAX];
+	int i, ret = EXIT_SUCCESS;
+
+	if (cg_find_unified_root(root, sizeof(root)))
+		ksft_exit_skip("cgroup v2 isn't mounted\n");
+	for (i = 0; i < ARRAY_SIZE(tests); i++) {
+		switch (tests[i].fn(root)) {
+		case KSFT_PASS:
+			ksft_test_result_pass("%s\n", tests[i].name);
+			break;
+		case KSFT_SKIP:
+			ksft_test_result_skip("%s\n", tests[i].name);
+			break;
+		default:
+			ret = EXIT_FAILURE;
+			ksft_test_result_fail("%s\n", tests[i].name);
+			break;
+		}
+	}
+
+	return ret;
+}
-- 
2.17.2