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+/*
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+ * cgroup_freezer.c - control group freezer subsystem
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+ *
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+ * Copyright IBM Corporation, 2007
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+ *
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+ * Author : Cedric Le Goater <clg@fr.ibm.com>
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+ *
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+ * This program is free software; you can redistribute it and/or modify it
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+ * under the terms of version 2.1 of the GNU Lesser General Public License
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+ * as published by the Free Software Foundation.
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+ *
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+ * This program is distributed in the hope that it would be useful, but
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+ * WITHOUT ANY WARRANTY; without even the implied warranty of
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+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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+ */
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+
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+#include <linux/module.h>
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+#include <linux/cgroup.h>
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+#include <linux/fs.h>
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+#include <linux/uaccess.h>
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+#include <linux/freezer.h>
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+#include <linux/seq_file.h>
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+
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+enum freezer_state {
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+ STATE_RUNNING = 0,
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+ STATE_FREEZING,
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+ STATE_FROZEN,
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+};
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+
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+struct freezer {
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+ struct cgroup_subsys_state css;
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+ enum freezer_state state;
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+ spinlock_t lock; /* protects _writes_ to state */
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+};
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+
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+static inline struct freezer *cgroup_freezer(
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+ struct cgroup *cgroup)
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+{
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+ return container_of(
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+ cgroup_subsys_state(cgroup, freezer_subsys_id),
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+ struct freezer, css);
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+}
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+
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+static inline struct freezer *task_freezer(struct task_struct *task)
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+{
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+ return container_of(task_subsys_state(task, freezer_subsys_id),
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+ struct freezer, css);
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+}
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+
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+int cgroup_frozen(struct task_struct *task)
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+{
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+ struct freezer *freezer;
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+ enum freezer_state state;
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+
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+ task_lock(task);
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+ freezer = task_freezer(task);
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+ state = freezer->state;
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+ task_unlock(task);
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+
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+ return state == STATE_FROZEN;
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+}
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+
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+/*
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+ * cgroups_write_string() limits the size of freezer state strings to
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+ * CGROUP_LOCAL_BUFFER_SIZE
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+ */
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+static const char *freezer_state_strs[] = {
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+ "RUNNING",
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+ "FREEZING",
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+ "FROZEN",
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+};
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+
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+/*
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+ * State diagram
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+ * Transitions are caused by userspace writes to the freezer.state file.
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+ * The values in parenthesis are state labels. The rest are edge labels.
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+ *
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+ * (RUNNING) --FROZEN--> (FREEZING) --FROZEN--> (FROZEN)
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+ * ^ ^ | |
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+ * | \_______RUNNING_______/ |
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+ * \_____________________________RUNNING___________/
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+ */
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+
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+struct cgroup_subsys freezer_subsys;
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+
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+/* Locks taken and their ordering
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+ * ------------------------------
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+ * css_set_lock
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+ * cgroup_mutex (AKA cgroup_lock)
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+ * task->alloc_lock (AKA task_lock)
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+ * freezer->lock
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+ * task->sighand->siglock
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+ *
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+ * cgroup code forces css_set_lock to be taken before task->alloc_lock
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+ *
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+ * freezer_create(), freezer_destroy():
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+ * cgroup_mutex [ by cgroup core ]
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+ *
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+ * can_attach():
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+ * cgroup_mutex
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+ *
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+ * cgroup_frozen():
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+ * task->alloc_lock (to get task's cgroup)
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+ *
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+ * freezer_fork() (preserving fork() performance means can't take cgroup_mutex):
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+ * task->alloc_lock (to get task's cgroup)
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+ * freezer->lock
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+ * sighand->siglock (if the cgroup is freezing)
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+ *
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+ * freezer_read():
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+ * cgroup_mutex
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+ * freezer->lock
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+ * read_lock css_set_lock (cgroup iterator start)
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+ *
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+ * freezer_write() (freeze):
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+ * cgroup_mutex
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+ * freezer->lock
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+ * read_lock css_set_lock (cgroup iterator start)
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+ * sighand->siglock
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+ *
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+ * freezer_write() (unfreeze):
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+ * cgroup_mutex
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+ * freezer->lock
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+ * read_lock css_set_lock (cgroup iterator start)
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+ * task->alloc_lock (to prevent races with freeze_task())
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+ * sighand->siglock
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+ */
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+static struct cgroup_subsys_state *freezer_create(struct cgroup_subsys *ss,
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+ struct cgroup *cgroup)
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+{
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+ struct freezer *freezer;
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+
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+ freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL);
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+ if (!freezer)
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+ return ERR_PTR(-ENOMEM);
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+
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+ spin_lock_init(&freezer->lock);
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+ freezer->state = STATE_RUNNING;
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+ return &freezer->css;
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+}
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+
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+static void freezer_destroy(struct cgroup_subsys *ss,
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+ struct cgroup *cgroup)
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+{
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+ kfree(cgroup_freezer(cgroup));
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+}
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+
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+
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+static int freezer_can_attach(struct cgroup_subsys *ss,
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+ struct cgroup *new_cgroup,
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+ struct task_struct *task)
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+{
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+ struct freezer *freezer;
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+ int retval = 0;
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+
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+ /*
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+ * The call to cgroup_lock() in the freezer.state write method prevents
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+ * a write to that file racing against an attach, and hence the
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+ * can_attach() result will remain valid until the attach completes.
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+ */
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+ freezer = cgroup_freezer(new_cgroup);
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+ if (freezer->state == STATE_FROZEN)
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+ retval = -EBUSY;
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+ return retval;
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+}
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+
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+static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task)
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+{
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+ struct freezer *freezer;
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+
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+ task_lock(task);
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+ freezer = task_freezer(task);
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+ task_unlock(task);
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+
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+ BUG_ON(freezer->state == STATE_FROZEN);
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+ spin_lock_irq(&freezer->lock);
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+ /* Locking avoids race with FREEZING -> RUNNING transitions. */
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+ if (freezer->state == STATE_FREEZING)
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+ freeze_task(task, true);
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+ spin_unlock_irq(&freezer->lock);
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+}
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+
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+/*
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+ * caller must hold freezer->lock
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+ */
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+static void check_if_frozen(struct cgroup *cgroup,
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+ struct freezer *freezer)
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+{
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+ struct cgroup_iter it;
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+ struct task_struct *task;
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+ unsigned int nfrozen = 0, ntotal = 0;
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+
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+ cgroup_iter_start(cgroup, &it);
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+ while ((task = cgroup_iter_next(cgroup, &it))) {
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+ ntotal++;
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+ /*
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+ * Task is frozen or will freeze immediately when next it gets
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+ * woken
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+ */
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+ if (frozen(task) ||
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+ (task_is_stopped_or_traced(task) && freezing(task)))
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+ nfrozen++;
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+ }
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+
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+ /*
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+ * Transition to FROZEN when no new tasks can be added ensures
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+ * that we never exist in the FROZEN state while there are unfrozen
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+ * tasks.
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+ */
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+ if (nfrozen == ntotal)
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+ freezer->state = STATE_FROZEN;
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+ cgroup_iter_end(cgroup, &it);
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+}
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+
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+static int freezer_read(struct cgroup *cgroup, struct cftype *cft,
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+ struct seq_file *m)
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+{
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+ struct freezer *freezer;
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+ enum freezer_state state;
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+
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+ if (!cgroup_lock_live_group(cgroup))
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+ return -ENODEV;
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+
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+ freezer = cgroup_freezer(cgroup);
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+ spin_lock_irq(&freezer->lock);
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+ state = freezer->state;
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+ if (state == STATE_FREEZING) {
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+ /* We change from FREEZING to FROZEN lazily if the cgroup was
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+ * only partially frozen when we exitted write. */
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+ check_if_frozen(cgroup, freezer);
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+ state = freezer->state;
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+ }
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+ spin_unlock_irq(&freezer->lock);
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+ cgroup_unlock();
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+
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+ seq_puts(m, freezer_state_strs[state]);
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+ seq_putc(m, '\n');
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+ return 0;
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+}
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+
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+static int try_to_freeze_cgroup(struct cgroup *cgroup, struct freezer *freezer)
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+{
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+ struct cgroup_iter it;
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+ struct task_struct *task;
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+ unsigned int num_cant_freeze_now = 0;
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+
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+ freezer->state = STATE_FREEZING;
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+ cgroup_iter_start(cgroup, &it);
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+ while ((task = cgroup_iter_next(cgroup, &it))) {
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+ if (!freeze_task(task, true))
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+ continue;
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+ if (task_is_stopped_or_traced(task) && freezing(task))
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+ /*
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+ * The freeze flag is set so these tasks will
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+ * immediately go into the fridge upon waking.
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+ */
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+ continue;
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+ if (!freezing(task) && !freezer_should_skip(task))
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+ num_cant_freeze_now++;
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+ }
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+ cgroup_iter_end(cgroup, &it);
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+
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+ return num_cant_freeze_now ? -EBUSY : 0;
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+}
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+
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+static int unfreeze_cgroup(struct cgroup *cgroup, struct freezer *freezer)
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+{
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+ struct cgroup_iter it;
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+ struct task_struct *task;
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+
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+ cgroup_iter_start(cgroup, &it);
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+ while ((task = cgroup_iter_next(cgroup, &it))) {
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+ int do_wake;
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+
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+ task_lock(task);
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+ do_wake = __thaw_process(task);
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+ task_unlock(task);
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+ if (do_wake)
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+ wake_up_process(task);
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+ }
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+ cgroup_iter_end(cgroup, &it);
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+ freezer->state = STATE_RUNNING;
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+
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+ return 0;
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+}
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+
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+static int freezer_change_state(struct cgroup *cgroup,
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+ enum freezer_state goal_state)
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+{
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+ struct freezer *freezer;
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+ int retval = 0;
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+
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+ freezer = cgroup_freezer(cgroup);
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+ spin_lock_irq(&freezer->lock);
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+ check_if_frozen(cgroup, freezer); /* may update freezer->state */
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+ if (goal_state == freezer->state)
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+ goto out;
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+ switch (freezer->state) {
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+ case STATE_RUNNING:
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+ retval = try_to_freeze_cgroup(cgroup, freezer);
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+ break;
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+ case STATE_FREEZING:
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+ if (goal_state == STATE_FROZEN) {
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+ /* Userspace is retrying after
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+ * "/bin/echo FROZEN > freezer.state" returned -EBUSY */
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+ retval = try_to_freeze_cgroup(cgroup, freezer);
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+ break;
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+ }
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+ /* state == FREEZING and goal_state == RUNNING, so unfreeze */
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+ case STATE_FROZEN:
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+ retval = unfreeze_cgroup(cgroup, freezer);
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+ break;
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+ default:
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+ break;
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+ }
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+out:
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+ spin_unlock_irq(&freezer->lock);
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+
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+ return retval;
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+}
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+
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+static int freezer_write(struct cgroup *cgroup,
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+ struct cftype *cft,
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+ const char *buffer)
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+{
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+ int retval;
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+ enum freezer_state goal_state;
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+
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+ if (strcmp(buffer, freezer_state_strs[STATE_RUNNING]) == 0)
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+ goal_state = STATE_RUNNING;
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+ else if (strcmp(buffer, freezer_state_strs[STATE_FROZEN]) == 0)
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+ goal_state = STATE_FROZEN;
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+ else
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+ return -EIO;
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+
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+ if (!cgroup_lock_live_group(cgroup))
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+ return -ENODEV;
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+ retval = freezer_change_state(cgroup, goal_state);
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+ cgroup_unlock();
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+ return retval;
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+}
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+
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+static struct cftype files[] = {
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+ {
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+ .name = "state",
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+ .read_seq_string = freezer_read,
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+ .write_string = freezer_write,
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+ },
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+};
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+
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+static int freezer_populate(struct cgroup_subsys *ss, struct cgroup *cgroup)
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+{
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+ return cgroup_add_files(cgroup, ss, files, ARRAY_SIZE(files));
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+}
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+
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+struct cgroup_subsys freezer_subsys = {
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+ .name = "freezer",
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+ .create = freezer_create,
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+ .destroy = freezer_destroy,
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+ .populate = freezer_populate,
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+ .subsys_id = freezer_subsys_id,
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+ .can_attach = freezer_can_attach,
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+ .attach = NULL,
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+ .fork = freezer_fork,
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+ .exit = NULL,
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+};
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Matt Helsley