lockdep && recursive-read

[Oleg Nesterov]

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.