path: root/kernel/freezer.c
diff options
authorMatt Helsley <>2008-10-18 20:27:21 -0700
committerLinus Torvalds <>2008-10-20 08:52:34 -0700
commitdc52ddc0e6f45b04780b26fc0813509f8e798c42 (patch)
tree384826e9fab4e434bc5c85ce744470ae472e52c3 /kernel/freezer.c
parent8174f1503f4bf7e9a14b3fbbfdb30c6be6e29f77 (diff)
container freezer: implement freezer cgroup subsystem
This patch implements a new freezer subsystem in the control groups framework. It provides a way to stop and resume execution of all tasks in a cgroup by writing in the cgroup filesystem. The freezer subsystem in the container filesystem defines a file named freezer.state. Writing "FROZEN" to the state file will freeze all tasks in the cgroup. Subsequently writing "RUNNING" will unfreeze the tasks in the cgroup. Reading will return the current state. * Examples of usage : # mkdir /containers/freezer # mount -t cgroup -ofreezer freezer /containers # mkdir /containers/0 # echo $some_pid > /containers/0/tasks to get status of the freezer subsystem : # cat /containers/0/freezer.state RUNNING to freeze all tasks in the container : # echo FROZEN > /containers/0/freezer.state # cat /containers/0/freezer.state FREEZING # cat /containers/0/freezer.state FROZEN to unfreeze all tasks in the container : # echo RUNNING > /containers/0/freezer.state # cat /containers/0/freezer.state RUNNING This is the basic mechanism which should do the right thing for user space task in a simple scenario. It's important to note that freezing can be incomplete. In that case we return EBUSY. This means that some tasks in the cgroup are busy doing something that prevents us from completely freezing the cgroup at this time. After EBUSY, the cgroup will remain partially frozen -- reflected by freezer.state reporting "FREEZING" when read. The state will remain "FREEZING" until one of these things happens: 1) Userspace cancels the freezing operation by writing "RUNNING" to the freezer.state file 2) Userspace retries the freezing operation by writing "FROZEN" to the freezer.state file (writing "FREEZING" is not legal and returns EIO) 3) The tasks that blocked the cgroup from entering the "FROZEN" state disappear from the cgroup's set of tasks. [ coding-style fixes] [ export thaw_process] Signed-off-by: Cedric Le Goater <> Signed-off-by: Matt Helsley <> Acked-by: Serge E. Hallyn <> Tested-by: Matt Helsley <> Signed-off-by: Andrew Morton <> Signed-off-by: Linus Torvalds <>
Diffstat (limited to 'kernel/freezer.c')
1 files changed, 32 insertions, 0 deletions
diff --git a/kernel/freezer.c b/kernel/freezer.c
index cb0931f89306..ba6248b323ef 100644
--- a/kernel/freezer.c
+++ b/kernel/freezer.c
@@ -120,3 +120,35 @@ void cancel_freezing(struct task_struct *p)
spin_unlock_irqrestore(&p->sighand->siglock, flags);
+ * Wake up a frozen process
+ *
+ * task_lock() is needed to prevent the race with refrigerator() which may
+ * occur if the freezing of tasks fails. Namely, without the lock, if the
+ * freezing of tasks failed, thaw_tasks() might have run before a task in
+ * refrigerator() could call frozen_process(), in which case the task would be
+ * frozen and no one would thaw it.
+ */
+int __thaw_process(struct task_struct *p)
+ if (frozen(p)) {
+ p->flags &= ~PF_FROZEN;
+ return 1;
+ }
+ clear_freeze_flag(p);
+ return 0;
+int thaw_process(struct task_struct *p)
+ task_lock(p);
+ if (__thaw_process(p) == 1) {
+ task_unlock(p);
+ wake_up_process(p);
+ return 1;
+ }
+ task_unlock(p);
+ return 0;