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Commit 3b1b3f6e authored by Li Zefan's avatar Li Zefan Committed by Linus Torvalds
Browse files

freezer_cg: disable writing freezer.state of root cgroup 



With this change, control file 'freezer.state' doesn't exist in root
cgroup, making root cgroup unfreezable.

I think it's reasonable to disallow freeze tasks in the root cgroup.  And
then we can avoid fork overhead when freezer subsystem is compiled but not
used.

Also make writing invalid value to freezer.state returns EINVAL rather
than EIO.  This is more consistent with other cgroup subsystem.

Signed-off-by: default avatarLi Zefan <lizf@cn.fujitsu.com>
Acked-by: default avatarPaul Menage <menage@google.com>
Cc: Cedric Le Goater <clg@fr.ibm.com>
Cc: Paul Menage <menage@google.com>
Cc: Matt Helsley <matthltc@us.ibm.com>
Cc: "Serge E. Hallyn" <serue@us.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 68744676

Documentation/cgroups/freezer-subsystem.txt

+12 −9
Original line number Diff line number Diff line
@@ -54,9 +54,12 @@ freezer.state. Writing "FROZEN" to the state file will freeze all tasks in the 
cgroup. Subsequently writing "THAWED" will unfreeze the tasks in the cgroup.

Reading will return the current state.



Note freezer.state doesn't exist in root cgroup, which means root cgroup

is non-freezable.



* Examples of usage :



   # mkdir /containers/freezer

   # mkdir /containers

   # mount -t cgroup -ofreezer freezer  /containers

   # mkdir /containers/0

   # echo $some_pid > /containers/0/tasks
@@ -94,6 +97,6 @@ things happens: 
		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)

		and returns EINVAL)

	3) The tasks that blocked the cgroup from entering the "FROZEN"

		state disappear from the cgroup's set of tasks.

kernel/cgroup_freezer.c

+10 −1
Original line number Diff line number Diff line
@@ -192,6 +192,13 @@ static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task) 
	 */

	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);
@@ -335,7 +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;
@@ -354,6 +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));

}