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From: Tomasz Buchert on 12 Aug 2010 05:50
It is possible to move a task from its cgroup
even if this group is 'FREEZING'. This results in
a nasty bug - the moved task will become frozen OUTSIDE
its original cgroup and will remain in a permanent 'D' state.

This patch allows to migrate the task only between THAWED cgroups.

This behavior was observed and easily reproduced on
a single core laptop. Notice that reproducibility depends
highly on the machine used. Program and instructions how
to reproduce the bug can be fetched from:
http://pentium.hopto.org/~thinred/repos/linux-misc/freezer_bug.c

Signed-off-by: Tomasz Buchert <tomasz.buchert(a)inria.fr>
---
kernel/cgroup_freezer.c | 15 ++++++++-------
1 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index 321e2a0..c287627 100644
--- a/kernel/cgroup_freezer.c
+++ b/kernel/cgroup_freezer.c
@@ -173,24 +173,25 @@ static int freezer_can_attach(struct cgroup_subsys *ss,

/*
* 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))
+ freezer = cgroup_freezer(new_cgroup);
+ if (freezer->state != CGROUP_THAWED)
return -EBUSY;

- freezer = cgroup_freezer(new_cgroup);
- if (freezer->state == CGROUP_FROZEN)
+ rcu_read_lock();
+ if (__cgroup_freezing_or_frozen(task)) {
+ rcu_read_unlock();
return -EBUSY;
+ }
+ rcu_read_unlock();

if (threadgroup) {
struct task_struct *c;

rcu_read_lock();
list_for_each_entry_rcu(c, &task->thread_group, thread_group) {
- if (is_task_frozen_enough(c)) {
+ if (__cgroup_freezing_or_frozen(c)) {
rcu_read_unlock();
return -EBUSY;
}
--
1.6.3.3

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Prev: [PATCH] alpha: convert perf_event to use local_t
Next: [PATCH] forcedeth: reconfigure multicast packet filter only when needed