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

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Message-Id: <20180418.133539.1514284482902646647.davem@davemloft.net>
Date:   Wed, 18 Apr 2018 13:35:39 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     liuxiang_1999@....com
Cc:     liu.xiang6@....com.cn, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] net: davicom: dm9000: Avoid spinlock recursion
 during dm9000_timeout routine

From: liuxiang  <liuxiang_1999@....com>
Date: Wed, 18 Apr 2018 21:48:22 +0800 (CST)

> Because the timeout task gets the main spinlock and disable the
> current cpu's irq, there is no other task on the same cpu can run,
> and tasks on the other cpus can not enter the dm9000_timeout()
> again. So in the whole dm9000_timeout() routine, db->timeout_cpu can
> not be changed by other tasks. Although smp_processor_id() may
> change after preempt_enable(), these tasks always get the false
> result when call dm9000_current_in_timeout.  Only the timeout task
> get the true result. And if there is no timeout, all the tasks that
> want to do asynchronous phy operation get the false result. So I
> think this can avoid racy.

This is a very shaky foundation upon which to base the correctness
of your driver's synchronization in my opinion.