container freezer: prevent frozen tasks or cgroups from changing
Don't let frozen tasks or cgroups change. This means frozen tasks can't
leave their current cgroup for another cgroup. It also means that tasks
cannot be added to or removed from a cgroup in the FROZEN state. We
enforce these rules by checking for frozen tasks and cgroups in the
can_attach() function.
Signed-off-by: Matt Helsley <matthltc@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index b08722d..df88402 100644
--- a/kernel/cgroup_freezer.c
+++ b/kernel/cgroup_freezer.c
@@ -145,22 +145,40 @@
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;
- int retval = 0;
+ int retval;
- /*
- * 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.
- */
+ /* Anything frozen can't move or be moved to/from */
+
+ if (is_task_frozen_enough(task))
+ return -EBUSY;
+
freezer = cgroup_freezer(new_cgroup);
if (freezer->state == STATE_FROZEN)
+ return -EBUSY;
+
+ retval = 0;
+ task_lock(task);
+ freezer = task_freezer(task);
+ if (freezer->state == STATE_FROZEN)
retval = -EBUSY;
+ task_unlock(task);
return retval;
}
@@ -193,12 +211,7 @@
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)))
+ if (is_task_frozen_enough(task))
nfrozen++;
}
@@ -249,11 +262,7 @@
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.
- */
+ if (is_task_frozen_enough(task))
continue;
if (!freezing(task) && !freezer_should_skip(task))
num_cant_freeze_now++;