--- /dev/null
+/*
+ * 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/module.h>
+#include <linux/cgroup.h>
+#include <linux/fs.h>
+#include <linux/uaccess.h>
+#include <linux/freezer.h>
+#include <linux/seq_file.h>
+
+enum freezer_state {
+ STATE_RUNNING = 0,
+ STATE_FREEZING,
+ STATE_FROZEN,
+};
+
+struct freezer {
+ struct cgroup_subsys_state css;
+ enum freezer_state state;
+ spinlock_t lock; /* protects _writes_ to state */
+};
+
+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);
+}
+
+int cgroup_frozen(struct task_struct *task)
+{
+ struct freezer *freezer;
+ enum freezer_state state;
+
+ task_lock(task);
+ freezer = task_freezer(task);
+ state = freezer->state;
+ task_unlock(task);
+
+ return state == STATE_FROZEN;
+}
+
+/*
+ * cgroups_write_string() limits the size of freezer state strings to
+ * CGROUP_LOCAL_BUFFER_SIZE
+ */
+static const char *freezer_state_strs[] = {
+ "RUNNING",
+ "FREEZING",
+ "FROZEN",
+};
+
+/*
+ * State diagram
+ * Transitions are caused by userspace writes to the freezer.state file.
+ * The values in parenthesis are state labels. The rest are edge labels.
+ *
+ * (RUNNING) --FROZEN--> (FREEZING) --FROZEN--> (FROZEN)
+ * ^ ^ | |
+ * | \_______RUNNING_______/ |
+ * \_____________________________RUNNING___________/
+ */
+
+struct cgroup_subsys freezer_subsys;
+
+/* Locks taken and their ordering
+ * ------------------------------
+ * css_set_lock
+ * cgroup_mutex (AKA cgroup_lock)
+ * task->alloc_lock (AKA task_lock)
+ * freezer->lock
+ * task->sighand->siglock
+ *
+ * cgroup code forces css_set_lock to be taken before task->alloc_lock
+ *
+ * freezer_create(), freezer_destroy():
+ * cgroup_mutex [ by cgroup core ]
+ *
+ * can_attach():
+ * cgroup_mutex
+ *
+ * cgroup_frozen():
+ * task->alloc_lock (to get task's cgroup)
+ *
+ * freezer_fork() (preserving fork() performance means can't take cgroup_mutex):
+ * task->alloc_lock (to get task's cgroup)
+ * freezer->lock
+ * sighand->siglock (if the cgroup is freezing)
+ *
+ * freezer_read():
+ * cgroup_mutex
+ * freezer->lock
+ * read_lock css_set_lock (cgroup iterator start)
+ *
+ * freezer_write() (freeze):
+ * cgroup_mutex
+ * freezer->lock
+ * read_lock css_set_lock (cgroup iterator start)
+ * sighand->siglock
+ *
+ * freezer_write() (unfreeze):
+ * cgroup_mutex
+ * freezer->lock
+ * read_lock css_set_lock (cgroup iterator start)
+ * task->alloc_lock (to prevent races with freeze_task())
+ * sighand->siglock
+ */
+static struct cgroup_subsys_state *freezer_create(struct cgroup_subsys *ss,
+ struct cgroup *cgroup)
+{
+ struct freezer *freezer;
+
+ freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL);
+ if (!freezer)
+ return ERR_PTR(-ENOMEM);
+
+ spin_lock_init(&freezer->lock);
+ freezer->state = STATE_RUNNING;
+ return &freezer->css;
+}
+
+static void freezer_destroy(struct cgroup_subsys *ss,
+ struct cgroup *cgroup)
+{
+ kfree(cgroup_freezer(cgroup));
+}
+
+
+static int freezer_can_attach(struct cgroup_subsys *ss,
+ struct cgroup *new_cgroup,
+ struct task_struct *task)
+{
+ struct freezer *freezer;
+ int retval = 0;
+
+ /*
+ * The call to cgroup_lock() in the freezer.state write method prevents
+ * a write to that file racing against an attach, and hence the
+ * can_attach() result will remain valid until the attach completes.
+ */
+ freezer = cgroup_freezer(new_cgroup);
+ if (freezer->state == STATE_FROZEN)
+ retval = -EBUSY;
+ return retval;
+}
+
+static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task)
+{
+ struct freezer *freezer;
+
+ task_lock(task);
+ freezer = task_freezer(task);
+ task_unlock(task);
+
+ BUG_ON(freezer->state == STATE_FROZEN);
+ spin_lock_irq(&freezer->lock);
+ /* Locking avoids race with FREEZING -> RUNNING transitions. */
+ if (freezer->state == STATE_FREEZING)
+ freeze_task(task, true);
+ spin_unlock_irq(&freezer->lock);
+}
+
+/*
+ * caller must hold freezer->lock
+ */
+static void check_if_frozen(struct cgroup *cgroup,
+ struct freezer *freezer)
+{
+ struct cgroup_iter it;
+ struct task_struct *task;
+ unsigned int nfrozen = 0, ntotal = 0;
+
+ cgroup_iter_start(cgroup, &it);
+ while ((task = cgroup_iter_next(cgroup, &it))) {
+ ntotal++;
+ /*
+ * Task is frozen or will freeze immediately when next it gets
+ * woken
+ */
+ if (frozen(task) ||
+ (task_is_stopped_or_traced(task) && freezing(task)))
+ nfrozen++;
+ }
+
+ /*
+ * Transition to FROZEN when no new tasks can be added ensures
+ * that we never exist in the FROZEN state while there are unfrozen
+ * tasks.
+ */
+ if (nfrozen == ntotal)
+ freezer->state = STATE_FROZEN;
+ cgroup_iter_end(cgroup, &it);
+}
+
+static int freezer_read(struct cgroup *cgroup, struct cftype *cft,
+ struct seq_file *m)
+{
+ struct freezer *freezer;
+ enum freezer_state state;
+
+ if (!cgroup_lock_live_group(cgroup))
+ return -ENODEV;
+
+ freezer = cgroup_freezer(cgroup);
+ spin_lock_irq(&freezer->lock);
+ state = freezer->state;
+ if (state == STATE_FREEZING) {
+ /* We change from FREEZING to FROZEN lazily if the cgroup was
+ * only partially frozen when we exitted write. */
+ check_if_frozen(cgroup, freezer);
+ state = freezer->state;
+ }
+ spin_unlock_irq(&freezer->lock);
+ cgroup_unlock();
+
+ seq_puts(m, freezer_state_strs[state]);
+ seq_putc(m, '\n');
+ return 0;
+}
+
+static int try_to_freeze_cgroup(struct cgroup *cgroup, struct freezer *freezer)
+{
+ struct cgroup_iter it;
+ struct task_struct *task;
+ unsigned int num_cant_freeze_now = 0;
+
+ freezer->state = STATE_FREEZING;
+ cgroup_iter_start(cgroup, &it);
+ while ((task = cgroup_iter_next(cgroup, &it))) {
+ if (!freeze_task(task, true))
+ continue;
+ if (task_is_stopped_or_traced(task) && freezing(task))
+ /*
+ * The freeze flag is set so these tasks will
+ * immediately go into the fridge upon waking.
+ */
+ continue;
+ if (!freezing(task) && !freezer_should_skip(task))
+ num_cant_freeze_now++;
+ }
+ cgroup_iter_end(cgroup, &it);
+
+ return num_cant_freeze_now ? -EBUSY : 0;
+}
+
+static int unfreeze_cgroup(struct cgroup *cgroup, struct freezer *freezer)
+{
+ struct cgroup_iter it;
+ struct task_struct *task;
+
+ cgroup_iter_start(cgroup, &it);
+ while ((task = cgroup_iter_next(cgroup, &it))) {
+ int do_wake;
+
+ task_lock(task);
+ do_wake = __thaw_process(task);
+ task_unlock(task);
+ if (do_wake)
+ wake_up_process(task);
+ }
+ cgroup_iter_end(cgroup, &it);
+ freezer->state = STATE_RUNNING;
+
+ return 0;
+}
+
+static int freezer_change_state(struct cgroup *cgroup,
+ enum freezer_state goal_state)
+{
+ struct freezer *freezer;
+ int retval = 0;
+
+ freezer = cgroup_freezer(cgroup);
+ spin_lock_irq(&freezer->lock);
+ check_if_frozen(cgroup, freezer); /* may update freezer->state */
+ if (goal_state == freezer->state)
+ goto out;
+ switch (freezer->state) {
+ case STATE_RUNNING:
+ retval = try_to_freeze_cgroup(cgroup, freezer);
+ break;
+ case STATE_FREEZING:
+ if (goal_state == STATE_FROZEN) {
+ /* Userspace is retrying after
+ * "/bin/echo FROZEN > freezer.state" returned -EBUSY */
+ retval = try_to_freeze_cgroup(cgroup, freezer);
+ break;
+ }
+ /* state == FREEZING and goal_state == RUNNING, so unfreeze */
+ case STATE_FROZEN:
+ retval = unfreeze_cgroup(cgroup, freezer);
+ break;
+ default:
+ break;
+ }
+out:
+ spin_unlock_irq(&freezer->lock);
+
+ return retval;
+}
+
+static int freezer_write(struct cgroup *cgroup,
+ struct cftype *cft,
+ const char *buffer)
+{
+ int retval;
+ enum freezer_state goal_state;
+
+ if (strcmp(buffer, freezer_state_strs[STATE_RUNNING]) == 0)
+ goal_state = STATE_RUNNING;
+ else if (strcmp(buffer, freezer_state_strs[STATE_FROZEN]) == 0)
+ goal_state = STATE_FROZEN;
+ else
+ return -EIO;
+
+ if (!cgroup_lock_live_group(cgroup))
+ return -ENODEV;
+ retval = freezer_change_state(cgroup, goal_state);
+ cgroup_unlock();
+ return retval;
+}
+
+static struct cftype files[] = {
+ {
+ .name = "state",
+ .read_seq_string = freezer_read,
+ .write_string = freezer_write,
+ },
+};
+
+static int freezer_populate(struct cgroup_subsys *ss, struct cgroup *cgroup)
+{
+ return cgroup_add_files(cgroup, ss, files, ARRAY_SIZE(files));
+}
+
+struct cgroup_subsys freezer_subsys = {
+ .name = "freezer",
+ .create = freezer_create,
+ .destroy = freezer_destroy,
+ .populate = freezer_populate,
+ .subsys_id = freezer_subsys_id,
+ .can_attach = freezer_can_attach,
+ .attach = NULL,
+ .fork = freezer_fork,
+ .exit = NULL,
+};
projects / karo-tx-linux.git / commitdiff