Re: 2.6.24-rc6: possible recursive locking detected

Oleg Nesterov
2008-01-07T17:47:26Z

On 01/07, Oleg Nesterov wrote:
>
> Consider this "just for illustration" patch,
>
> --- t/kernel/lockdep.c 2007-11-09 12:57:31.000000000 +0300
> +++ t/kernel/lockdep.c 2008-01-07 19:43:50.000000000 +0300
> @@ -1266,10 +1266,13 @@ check_deadlock(struct task_struct *curr,
> struct held_lock *prev;
> int i;
>
> - for (i = 0; i < curr->lockdep_depth; i++) {
> + for (i = curr->lockdep_depth; --i >= 0; ) {
> prev = curr->held_locks + i;
> if (prev->class != next->class)
> continue;
> +
> + if (prev->trylock == -1)
> + return 2;
> /*
> * Allow read-after-read recursion of the same
> * lock class (i.e. read_lock(lock)+read_lock(lock)):
> -------------------------------------------------------------------------
>
> Now,
>
> // trylock == -1
> #define spin_mark_nested(l) \
> lock_acquire(&(l)->dep_map, 0, -1, 0, 2, _THIS_IP_)
> #define spin_unmark_nested(l) \
> lock_release(&(l)->dep_map, 1, _THIS_IP_)
>
> and ep_poll_safewake() can do:
>
> /* Do really wake up now */
> spin_mark_nested(&wq->lock);
> wake_up(wq);
> spin_unmark_nested(&wq->lock);

I tested the patch above with the following code,

wait_queue_head_t w1, w2, w3;

init_waitqueue_head(&w1);
init_waitqueue_head(&w2);
init_waitqueue_head(&w3);

local_irq_disable();
spin_lock(&w1.lock);

spin_mark_nested(&w2.lock);
spin_lock(&w2.lock);

spin_mark_nested(&w3.lock);
wake_up(&w3);
spin_unmark_nested(&w3.lock);

spin_unlock(&w2.lock);
spin_unmark_nested(&w2.lock);

spin_unlock(&w1.lock);
local_irq_enable();

seems to work. What do you think?

Oleg.