From: "jianchao.wang" <jianchao.w.wang@oracle.com>
To: Ming Lei <ming.lei@redhat.com>, linux-kernel@vger.kernel.org
Cc: 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()
Date: Wed, 19 Sep 2018 13:19:10 +0800 [thread overview]
Message-ID: <242969d0-1370-b342-025d-a11b7f59d28f@oracle.com> (raw)
In-Reply-To: <20180918101946.13329-3-ming.lei@redhat.com>
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
next prev parent reply other threads:[~2018-09-19 10:55 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20180918101946.13329-1-ming.lei@redhat.com>
2018-09-18 10:19 ` [PATCH 1/4] percpu-refcount: move zeroing of percpu part into percpu_ref_switch_to_atomic_rcu Ming Lei
2018-09-18 10:19 ` [PATCH 2/4] lib/percpu-refcount: introduce percpu_ref_resurge() Ming Lei
2018-09-18 12:50 ` Tejun Heo
2018-09-19 3:09 ` Ming Lei
2018-09-19 5:19 ` jianchao.wang [this message]
2018-09-19 7:55 ` Ming Lei
2018-09-19 8:01 ` Ming Lei
2018-09-18 10:19 ` [PATCH 3/4] blk-mq: introduce blk_mq_unfreeze_queue_no_drain_io Ming Lei
2018-09-18 10:19 ` [PATCH 4/4] nvme: don't drain IO in nvme_reset_work() Ming Lei
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