Re: [PATCH tip/core/urgent 4/7] rcu: protect __rcu_read_unlock()against scheduler-using irq handlers

From: Peter Zijlstra
Date: Wed Jul 20 2011 - 08:55:36 EST


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?
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