linux-kernel - Re: [PATCH v3] net: davicom: dm9000: Avoid spinlock recursion during dm9000

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Date:   Mon, 16 Apr 2018 11:05:01 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     liu.xiang6@....com.cn
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        liuxiang_1999@....com
Subject: Re: [PATCH v3] net: davicom: dm9000: Avoid spinlock recursion
 during dm9000_timeout routine

From: Liu Xiang <liu.xiang6@....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.