cgroups: add cpu_relax() calls in css_tryget() and cgroup_clear_css_refs()

[safe/jmp/linux-2.6] / kernel / cgroup_freezer.c

diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index e9c856a..fb249e2 100644 (file)
--- a/kernel/cgroup_freezer.c
+++ b/kernel/cgroup_freezer.c
@@ -184,9 +184,20 @@ static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task)
 {
        struct freezer *freezer;
 
-       task_lock(task);
+       /*
+        * 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);
-       task_unlock(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);
@@ -275,25 +286,18 @@ static int try_to_freeze_cgroup(struct cgroup *cgroup, struct freezer *freezer)
        return num_cant_freeze_now ? -EBUSY : 0;
 }
 
-static int unfreeze_cgroup(struct cgroup *cgroup, struct freezer *freezer)
+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))) {
-               int do_wake;
-
-               task_lock(task);
-               do_wake = __thaw_process(task);
-               task_unlock(task);
-               if (do_wake)
-                       wake_up_process(task);
+               thaw_process(task);
        }
        cgroup_iter_end(cgroup, &it);
-       freezer->state = CGROUP_THAWED;
 
-       return 0;
+       freezer->state = CGROUP_THAWED;
 }
 
 static int freezer_change_state(struct cgroup *cgroup,
@@ -303,27 +307,22 @@ static int freezer_change_state(struct cgroup *cgroup,
        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 (freezer->state) {
+
+       switch (goal_state) {
        case CGROUP_THAWED:
-               retval = try_to_freeze_cgroup(cgroup, freezer);
+               unfreeze_cgroup(cgroup, freezer);
                break;
-       case CGROUP_FREEZING:
-               if (goal_state == CGROUP_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 == THAWED, so unfreeze */
        case CGROUP_FROZEN:
-               retval = unfreeze_cgroup(cgroup, freezer);
+               retval = try_to_freeze_cgroup(cgroup, freezer);
                break;
        default:
-               break;
+               BUG();
        }
 out:
        spin_unlock_irq(&freezer->lock);
@@ -343,7 +342,7 @@ static int freezer_write(struct cgroup *cgroup,
        else if (strcmp(buffer, freezer_state_strs[CGROUP_FROZEN]) == 0)
                goal_state = CGROUP_FROZEN;
        else
-               return -EIO;
+               return -EINVAL;
 
        if (!cgroup_lock_live_group(cgroup))
                return -ENODEV;
@@ -362,6 +361,8 @@ static struct cftype files[] = {
 
 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));
 }