On Tue, 2011-07-19 at 17:18 -0700, Paul E. McKenney wrote:
> @@ -391,10 +400,15 @@ void __rcu_read_unlock(void)
>         struct task_struct *t = current;
> 
>         barrier();  /* needed if we ever invoke rcu_read_unlock in rcutree.c */
> -       if (--t->rcu_read_lock_nesting == 0) {
> -               barrier();  /* decr before ->rcu_read_unlock_special load */
> +       if (t->rcu_read_lock_nesting != 1)
> +               --t->rcu_read_lock_nesting;
> +       else {
> +               t->rcu_read_lock_nesting = INT_MIN;
> +               barrier();  /* assign before ->rcu_read_unlock_special load */
>                 if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
>                         rcu_read_unlock_special(t);
> +               barrier();  /* ->rcu_read_unlock_special load before assign */
> +               t->rcu_read_lock_nesting = 0;
>         }
>  #ifdef CONFIG_PROVE_LOCKING
>         WARN_ON_ONCE(ACCESS_ONCE(t->rcu_read_lock_nesting) < 0); 

But won't the above change make that WARN_ON_ONCE() invalid?