1 files changed, 488 insertions, 0 deletions
diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
new file mode 100644
index 00000000..75dda1ea
--- /dev/null
+++ b/kernel/cgroup_freezer.c
@@ -0,0 +1,488 @@
+/*
+ * 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 *cgroup_freezer(struct cgroup *cgroup)
+{
+	return container_of(cgroup_subsys_state(cgroup, freezer_subsys_id),
+			    struct freezer, css);
+}
+
+static inline struct freezer *task_freezer(struct task_struct *task)
+{
+	return container_of(task_subsys_state(task, freezer_subsys_id),
+			    struct freezer, css);
+}
+
+static struct freezer *parent_freezer(struct freezer *freezer)
+{
+	struct cgroup *pcg = freezer->css.cgroup->parent;
+
+	if (pcg)
+		return cgroup_freezer(pcg);
+	return NULL;
+}
+
+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 *cgroup)
+{
+	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 cgroup
+ * @cgroup: cgroup being created
+ *
+ * We're committing to creation of @cgroup.  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 *cgroup)
+{
+	struct freezer *freezer = cgroup_freezer(cgroup);
+	struct freezer *parent = parent_freezer(freezer);
+
+	/*
+	 * The following double locking and freezing state inheritance
+	 * guarantee that @cgroup can never escape ancestors' freezing
+	 * states.  See cgroup_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 @cgroup
+ * @cgroup: cgroup being destroyed
+ *
+ * @cgroup is going away.  Mark it dead and decrement system_freezing_count
+ * if it was holding one.
+ */
+static void freezer_css_offline(struct cgroup *cgroup)
+{
+	struct freezer *freezer = cgroup_freezer(cgroup);
+
+	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 *cgroup)
+{
+	kfree(cgroup_freezer(cgroup));
+}
+
+/*
+ * 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 *new_cgrp, struct cgroup_taskset *tset)
+{
+	struct freezer *freezer = cgroup_freezer(new_cgrp);
+	struct task_struct *task;
+	bool clear_frozen = false;
+
+	spin_lock_irq(&freezer->lock);
+
+	/*
+	 * Make the new tasks conform to the current state of @new_cgrp.
+	 * 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_cgrp 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_cgrp, 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 (!freezer->css.cgroup->parent)
+		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
+ * @cgroup: cgroup 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 @cgroup, so we can't verify task states against
+ * @freezer state here.  See freezer_attach() for details.
+ */
+static void update_if_frozen(struct cgroup *cgroup)
+{
+	struct freezer *freezer = cgroup_freezer(cgroup);
+	struct cgroup *pos;
+	struct cgroup_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? */
+	cgroup_for_each_child(pos, cgroup) {
+		struct freezer *child = cgroup_freezer(pos);
+
+		if ((child->state & CGROUP_FREEZER_ONLINE) &&
+		    !(child->state & CGROUP_FROZEN))
+			goto out_unlock;
+	}
+
+	/* are all tasks frozen? */
+	cgroup_iter_start(cgroup, &it);
+
+	while ((task = cgroup_iter_next(cgroup, &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:
+	cgroup_iter_end(cgroup, &it);
+out_unlock:
+	spin_unlock_irq(&freezer->lock);
+}
+
+static int freezer_read(struct cgroup *cgroup, struct cftype *cft,
+			struct seq_file *m)
+{
+	struct cgroup *pos;
+
+	rcu_read_lock();
+
+	/* update states bottom-up */
+	cgroup_for_each_descendant_post(pos, cgroup)
+		update_if_frozen(pos);
+	update_if_frozen(cgroup);
+
+	rcu_read_unlock();
+
+	seq_puts(m, freezer_state_strs(cgroup_freezer(cgroup)->state));
+	seq_putc(m, '\n');
+	return 0;
+}
+
+static void freeze_cgroup(struct freezer *freezer)
+{
+	struct cgroup *cgroup = freezer->css.cgroup;
+	struct cgroup_iter it;
+	struct task_struct *task;
+
+	cgroup_iter_start(cgroup, &it);
+	while ((task = cgroup_iter_next(cgroup, &it)))
+		freeze_task(task);
+	cgroup_iter_end(cgroup, &it);
+}
+
+static void unfreeze_cgroup(struct freezer *freezer)
+{
+	struct cgroup *cgroup = freezer->css.cgroup;
+	struct cgroup_iter it;
+	struct task_struct *task;
+
+	cgroup_iter_start(cgroup, &it);
+	while ((task = cgroup_iter_next(cgroup, &it)))
+		__thaw_task(task);
+	cgroup_iter_end(cgroup, &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 *pos;
+
+	/* update @freezer */
+	spin_lock_irq(&freezer->lock);
+	freezer_apply_state(freezer, freeze, CGROUP_FREEZING_SELF);
+	spin_unlock_irq(&freezer->lock);
+
+	/*
+	 * 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();
+	cgroup_for_each_descendant_pre(pos, freezer->css.cgroup) {
+		struct freezer *pos_f = cgroup_freezer(pos);
+		struct freezer *parent = parent_freezer(pos_f);
+
+		/*
+		 * 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().
+		 */
+		spin_lock_irq(&pos_f->lock);
+		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 *cgroup, 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(cgroup_freezer(cgroup), freeze);
+	return 0;
+}
+
+static u64 freezer_self_freezing_read(struct cgroup *cgroup, struct cftype *cft)
+{
+	struct freezer *freezer = cgroup_freezer(cgroup);
+
+	return (bool)(freezer->state & CGROUP_FREEZING_SELF);
+}
+
+static u64 freezer_parent_freezing_read(struct cgroup *cgroup, struct cftype *cft)
+{
+	struct freezer *freezer = cgroup_freezer(cgroup);
+
+	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,
+};