diff options
| -rw-r--r-- | kernel/cgroup_freezer.c | 28 |
1 files changed, 25 insertions, 3 deletions
diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c index 7201a637c405..2ea98b216bff 100644 --- a/kernel/cgroup_freezer.c +++ b/kernel/cgroup_freezer.c @@ -214,6 +214,16 @@ static void freezer_attach(struct cgroup_subsys_state *new_css, } } +/** + * freezer_fork - cgroup post fork callback + * @task: a task which has just been forked + * + * @task has just been created and should conform to the current state of + * the cgroup_freezer it belongs to. This function may race against + * freezer_attach(). Losing to freezer_attach() means that we don't have + * to do anything as freezer_attach() will put @task into the appropriate + * state. + */ static void freezer_fork(struct task_struct *task) { struct freezer *freezer; @@ -222,14 +232,26 @@ static void freezer_fork(struct task_struct *task) freezer = task_freezer(task); /* - * The root cgroup is non-freezable, so we can skip the - * following check. + * The root cgroup is non-freezable, so we can skip locking the + * freezer. This is safe regardless of race with task migration. + * If we didn't race or won, skipping is obviously the right thing + * to do. If we lost and root is the new cgroup, noop is still the + * right thing to do. */ if (!parent_freezer(freezer)) goto out; + /* + * Grab @freezer->lock and freeze @task after verifying @task still + * belongs to @freezer and it's freezing. The former is for the + * case where we have raced against task migration and lost and + * @task is already in a different cgroup which may not be frozen. + * This isn't strictly necessary as freeze_task() is allowed to be + * called spuriously but let's do it anyway for, if nothing else, + * documentation. + */ spin_lock_irq(&freezer->lock); - if (freezer->state & CGROUP_FREEZING) + if (freezer == task_freezer(task) && (freezer->state & CGROUP_FREEZING)) freeze_task(task); spin_unlock_irq(&freezer->lock); out: |