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Date: Thu, 2 Nov 2017 13:10:59 -0400
From: Steven Rostedt <rostedt@goodmis.org>
To: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: akpm@linux-foundation.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Cong Wang <xiyou.wangcong@gmail.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Johannes Weiner <hannes@cmpxchg.org>, Mel Gorman <mgorman@suse.de>,
        Michal Hocko <mhocko@kernel.org>, Petr Mladek <pmladek@suse.com>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        "yuwang.yuwang" <yuwang.yuwang@alibaba-inc.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Jan Kara <jack@suse.cz>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Subject: Re: [PATCH v2] printk: Add console owner and waiter logic to load
 balance console writes
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On Thu, 2 Nov 2017 13:06:05 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> +		raw_spin_lock(&console_owner_lock);
> +		waiter = console_waiter;
> +		console_owner = NULL;
> +		raw_spin_unlock(&console_owner_lock);
> +
> +		/*
> +		 * If there is a waiter waiting for us, then pass the
> +		 * rest of the work load over to that waiter.
> +		 */
> +		if (waiter)
> +			break;
> +

Hmm, do I need a READ_ONCE() here?

Can gcc do the load of console_waiter outside the spin lock where 
if (waiter) is done?

Although it doesn't really matter, but it just makes the code more
fragile if it can. Should this be:

		raw_spin_lock(&console_owner_lock);
		waiter = READ_ONCE(console_waiter);
		console_owner = NULL;
		raw_spin_unlock(&console_owner_lock);

		/*
		 * If there is a waiter waiting for us, then pass the
		 * rest of the work load over to that waiter.
		 */
		if (waiter)
			break;

 ?

-- Steve