1 files changed, 379 insertions, 0 deletions

diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
new file mode 100644
index 000000000000..fb249e2bcada
--- /dev/null
+++ b/kernel/cgroup_freezer.c
@@ -0,0 +1,379 @@
+/*
+ * 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 {
+        CGROUP_THAWED = 0,
+        CGROUP_FREEZING,
+        CGROUP_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 == CGROUP_FROZEN;
+}
+
+/*
+ * cgroups_write_string() limits the size of freezer state strings to
+ * CGROUP_LOCAL_BUFFER_SIZE
+ */
+static const char *freezer_state_strs[] = {
+        "THAWED",
+        "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.
+ *
+ * (THAWED) --FROZEN--> (FREEZING) --FROZEN--> (FROZEN)
+ *    ^ ^                    |                     |
+ *    | \_______THAWED_______/                     |
+ *    \__________________________THAWED____________/
+ */
+
+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 = CGROUP_THAWED;
+        return &freezer->css;
+}
+
+static void freezer_destroy(struct cgroup_subsys *ss,
+                            struct cgroup *cgroup)
+{
+        kfree(cgroup_freezer(cgroup));
+}
+
+/* Task is frozen or will freeze immediately when next it gets woken */
+static bool is_task_frozen_enough(struct task_struct *task)
+{
+        return frozen(task) ||
+                (task_is_stopped_or_traced(task) && freezing(task));
+}
+
+/*
+ * 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.
+ */
+static int freezer_can_attach(struct cgroup_subsys *ss,
+                              struct cgroup *new_cgroup,
+                              struct task_struct *task)
+{
+        struct freezer *freezer;
+
+        /*
+         * Anything frozen can't move or be moved to/from.
+         *
+         * Since orig_freezer->state == FROZEN means that @task has been
+         * frozen, so it's sufficient to check the latter condition.
+         */
+
+        if (is_task_frozen_enough(task))
+                return -EBUSY;
+
+        freezer = cgroup_freezer(new_cgroup);
+        if (freezer->state == CGROUP_FROZEN)
+                return -EBUSY;
+
+        return 0;
+}
+
+static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task)
+{
+        struct freezer *freezer;
+
+        /*
+         * No lock is needed, since the task isn't on tasklist yet,
+         * so it can't be moved to another cgroup, which means the
+         * freezer won't be removed and will be valid during this
+         * function call.
+         */
+        freezer = task_freezer(task);
+
+        /*
+         * The root cgroup is non-freezable, so we can skip the
+         * following check.
+         */
+        if (!freezer->css.cgroup->parent)
+                return;
+
+        spin_lock_irq(&freezer->lock);
+        BUG_ON(freezer->state == CGROUP_FROZEN);
+
+        /* Locking avoids race with FREEZING -> THAWED transitions. */
+        if (freezer->state == CGROUP_FREEZING)
+                freeze_task(task, true);
+        spin_unlock_irq(&freezer->lock);
+}
+
+/*
+ * caller must hold freezer->lock
+ */
+static void update_freezer_state(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++;
+                if (is_task_frozen_enough(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 = CGROUP_FROZEN;
+        else if (nfrozen > 0)
+                freezer->state = CGROUP_FREEZING;
+        else
+                freezer->state = CGROUP_THAWED;
+        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 == CGROUP_FREEZING) {
+                /* We change from FREEZING to FROZEN lazily if the cgroup was
+                 * only partially frozen when we exitted write. */
+                update_freezer_state(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 = CGROUP_FREEZING;
+        cgroup_iter_start(cgroup, &it);
+        while ((task = cgroup_iter_next(cgroup, &it))) {
+                if (!freeze_task(task, true))
+                        continue;
+                if (is_task_frozen_enough(task))
+                        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 void 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))) {
+                thaw_process(task);
+        }
+        cgroup_iter_end(cgroup, &it);
+
+        freezer->state = CGROUP_THAWED;
+}
+
+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);
+
+        update_freezer_state(cgroup, freezer);
+        if (goal_state == freezer->state)
+                goto out;
+
+        switch (goal_state) {
+        case CGROUP_THAWED:
+                unfreeze_cgroup(cgroup, freezer);
+                break;
+        case CGROUP_FROZEN:
+                retval = try_to_freeze_cgroup(cgroup, freezer);
+                break;
+        default:
+                BUG();
+        }
+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[CGROUP_THAWED]) == 0)
+                goal_state = CGROUP_THAWED;
+        else if (strcmp(buffer, freezer_state_strs[CGROUP_FROZEN]) == 0)
+                goal_state = CGROUP_FROZEN;
+        else
+                return -EINVAL;
+
+        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)
+{
+        if (!cgroup->parent)
+                return 0;
+        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,
+};