Hi Ming

On 09/18/2018 06:19 PM, Ming Lei wrote:

+		unsigned long __percpu *percpu_count;
+
+		WARN_ON_ONCE(__ref_is_percpu(ref, &percpu_count));
+
+		/* get one extra ref for avoiding race with .release */
+		rcu_read_lock_sched();
+		atomic_long_add(1, &ref->count);
+		rcu_read_unlock_sched();
+	}

The rcu_read_lock_sched here is redundant. We have been in the critical section
of a spin_lock_irqsave.

The atomic_long_add(1, &ref->count) may have two result.
1. ref->count > 1
   it will not drop to zero any more.
2. ref->count == 1
   it has dropped to zero and .release may be running.

Thanks
Jianchao