From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Miller <davem@davemloft.net>
Subject: Re: [PATCH v3] net: davicom: dm9000: Avoid spinlock recursion
 during dm9000_timeout routine
Date: Mon, 16 Apr 2018 11:05:01 -0400 (EDT)
Message-ID: <20180416.110501.92472500114183248.davem@davemloft.net>
References: <1523695834-6261-1-git-send-email-liu.xiang6@zte.com.cn>
Mime-Version: 1.0
Content-Type: Text/Plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        liuxiang_1999@126.com
To: liu.xiang6@zte.com.cn
Return-path: <linux-kernel-owner@vger.kernel.org>
In-Reply-To: <1523695834-6261-1-git-send-email-liu.xiang6@zte.com.cn>
Sender: linux-kernel-owner@vger.kernel.org
List-Id: netdev.vger.kernel.org

From: Liu Xiang <liu.xiang6@zte.com.cn>
Date: Sat, 14 Apr 2018 16:50:34 +0800

> +static bool dm9000_current_in_timeout(struct board_info *db)
> +{
> +	bool ret = false;
> +
> +	preempt_disable();
> +	ret = (db->timeout_cpu == smp_processor_id());
> +	preempt_enable();

This doesn't work.

As soon as you do preempt_enable(), smp_processor_id() can change.