Re: [PATCH] init: Fix race between init and kthreadd -v2

Ingo Molnar
2010-06-28T14:19:39Z

* Peter Zijlstra <peterz@infradead.org> wrote:

> +static __initdata DEFINE_MUTEX(kthreadd_lock);

> + /*
> + * We need to spawn init first so that it obtains pid-1, however
> + * the init task will end up wanting to create kthreads, which
> + * if we schedule it before we create kthreadd, will OOPS.
> + */
> + mutex_lock(&kthreadd_lock);
> kernel_thread(kernel_init, NULL, CLONE_FS | CLONE_SIGHAND);
> numa_default_policy();
> pid = kernel_thread(kthreadd, NULL, CLONE_FS | CLONE_FILES);
> rcu_read_lock();
> kthreadd_task = find_task_by_pid_ns(pid, &init_pid_ns);
> rcu_read_unlock();
> + mutex_unlock(&kthreadd_lock);
> unlock_kernel();
>
> /*
> @@ -847,6 +856,13 @@ static noinline int init_post(void)
>
> static int __init kernel_init(void * unused)
> {
> + /*
> + * We spawned this thread while holding this lock, ensure the
> + * locked section in rest_init() is complete before proceeding.
> + */
> + mutex_lock(&kthreadd_lock);
> + mutex_unlock(&kthreadd_lock);

I think you may be using a mutex as a completion in essence. Why not use
completions instead?

Ingo