[PATCH] cgroup_freezer: Freezing and task move race fix
in [Kernel]
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From: Tomasz Buchert on 10 Aug 2010 16:00 Writing 'FROZEN' to freezer.state file does not forbid the task to be moved away from its cgroup (for a very short time). Nevertheless the moved task can become frozen OUTSIDE its cgroup which puts discussed task in a permanent 'D' state. This patch forbids migration of either FROZEN or FREEZING tasks. This behavior was observed and easily reproduced on a single core laptop. 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 | 10 ++++++++-- 1 files changed, 8 insertions(+), 2 deletions(-) diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c index ce71ed5..e49aa8c 100644 --- a/kernel/cgroup_freezer.c +++ b/kernel/cgroup_freezer.c @@ -161,6 +161,12 @@ static bool is_task_frozen_enough(struct task_struct *task) (task_is_stopped_or_traced(task) && freezing(task)); } +/* Task is in a state that forbids any cgroup migration. */ +static bool is_task_pinned_down(struct task_struct *task) +{ + return freezing(task) || frozen(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 @@ -179,7 +185,7 @@ static int freezer_can_attach(struct cgroup_subsys *ss, * frozen, so it's sufficient to check the latter condition. */ - if (is_task_frozen_enough(task)) + if (is_task_pinned_down(task)) return -EBUSY; freezer = cgroup_freezer(new_cgroup); @@ -191,7 +197,7 @@ static int freezer_can_attach(struct cgroup_subsys *ss, rcu_read_lock(); list_for_each_entry_rcu(c, &task->thread_group, thread_group) { - if (is_task_frozen_enough(c)) { + if (is_task_pinned_down(c)) { rcu_read_unlock(); return -EBUSY; } -- 1.6.3.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |