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SubjectRe: [PATCH 2/4] lib/percpu-refcount: introduce percpu_ref_resurge()
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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


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