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Date: Wed, 19 Sep 2018 15:55:07 +0800
From: Ming Lei <ming.lei@redhat.com>
To: "jianchao.wang" <jianchao.w.wang@oracle.com>
Cc: linux-kernel@vger.kernel.org, Tejun Heo <tj@kernel.org>,
        Kent Overstreet <kent.overstreet@gmail.com>,
        linux-block@vger.kernel.org
Subject: Re: [PATCH 2/4] lib/percpu-refcount: introduce percpu_ref_resurge()
Message-ID: <20180919075506.GA23172@ming.t460p>
References: <20180918101946.13329-1-ming.lei@redhat.com>
 <20180918101946.13329-3-ming.lei@redhat.com>
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On Wed, Sep 19, 2018 at 01:19:10PM +0800, jianchao.wang wrote:
> 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.

Right.

> 
> 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.

IMO, both the two cases are fine and supported, or do you have other
concern about this way?

thanks, 
Ming