Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH] block/elevator: reduce the critical section
To:     Hui Su <sh_def@163.com>, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20201019164246.GA79115@rlk>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <e63eb362-a1fc-f746-b5cb-b58d76fd3d06@kernel.dk>
Date:   Mon, 19 Oct 2020 10:50:32 -0600
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.10.0
MIME-Version: 1.0
In-Reply-To: <20201019164246.GA79115@rlk>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 10/19/20 10:42 AM, Hui Su wrote:
> 1.reduce the critical section in elevator_get().
> 2.reduce the critical section in elevator_get_by_features().
> 3.remove the found variable.
> 
> the elv_list_lock is used to protect the elv_list,
> and the operations of elevator_type does not need
> to be protected.
> 
> Signed-off-by: Hui Su <sh_def@163.com>
> ---
>  block/elevator.c | 14 ++++++--------
>  1 file changed, 6 insertions(+), 8 deletions(-)
> 
> diff --git a/block/elevator.c b/block/elevator.c
> index 293c5c81397a..727902b31954 100644
> --- a/block/elevator.c
> +++ b/block/elevator.c
> @@ -151,11 +151,11 @@ static struct elevator_type *elevator_get(struct request_queue *q,
>  		spin_lock(&elv_list_lock);
>  		e = elevator_find(name, q->required_elevator_features);
>  	}
> +	spin_unlock(&elv_list_lock);
>  
>  	if (e && !try_module_get(e->elevator_owner))
>  		e = NULL;
>  
> -	spin_unlock(&elv_list_lock);
>  	return e;
>  }

What happens for:

	A					B
	spin_unlock(&elv_list_lock);
						rmmod -> elv_unregister();
	try_module_get();

-- 
Jens Axboe