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 <[email protected]> --- 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 _______________________________________________ Containers mailing list [email protected] https://lists.linux-foundation.org/mailman/listinfo/containers _______________________________________________ Devel mailing list [email protected] https://openvz.org/mailman/listinfo/devel
