lockdep && recursive-read

[Oleg Nesterov <oleg@redhat.com>]

On 08/29, Oleg Nesterov wrote:
>
> Plus process_one_work() does lock_map_acquire_read(), I don't really
> understand this too.

and in fact I don't understand lock_map_acquire_read() itself. I mean, read == 2
and this code in check_prevs_add()

		/*
		 * Only non-recursive-read entries get new dependencies
		 * added:
		 */
		if (hlock->read != 2 && hlock->check) {
			if (!check_prev_add(curr, hlock, next,
						distance, &stack_saved))


Well, I forgot everything I ever knew about lockdep, unlikely I understand what
the code above actually does. But I verified that this code

		static DEFINE_SPINLOCK(exlk);
		static DEFINE_RWLOCK(rwlk);

		spin_lock(&exlk);
		write_lock(&rwlk);
		write_unlock(&rwlk);
		spin_unlock(&exlk);

		read_lock(&rwlk);
		spin_lock(&exlk);
		spin_unlock(&exlk);
		read_unlock(&rwlk);

runs without any warning from lockdep. Doesn't look right or I am totally
confused...

Oleg.