linux-kernel - Re: [RFC PATCH] printk: Use ACCESS_ONCE() instead of a volatile type

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Message-ID: <20141114115749.1514ec0a@gandalf.local.home>
Date:	Fri, 14 Nov 2014 11:57:49 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Alex Elder <elder@...aro.org>
Cc:	Pranith Kumar <bobby.prani@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Petr Mladek <pmladek@...e.cz>, Jan Kara <jack@...e.cz>,
	"Luis R. Rodriguez" <mcgrof@...e.com>,
	Joe Perches <joe@...ches.com>,
	open list <linux-kernel@...r.kernel.org>,
	paulmck@...ux.vnet.ibm.com
Subject: Re: [RFC PATCH] printk: Use ACCESS_ONCE() instead of a volatile
 type

On Fri, 14 Nov 2014 10:39:34 -0600
Alex Elder <elder@...aro.org> wrote:
 
> There is only one read of logbuf_cpu:
>         if (unlikely(logbuf_cpu == this_cpu)) {
> This is called only while local interrupts are disabled, so
> if this condition holds it cannot be due to an interrupt--it

Unless an NMI called printk.

> must be due to simple recursion into printk() while inside
> the spinlock-protected critical section.


> QED.  (Well, please correct me where I'm wrong...)
> 

Except for the NMI case, I believe you are correct with the rest of
your analysis.

-- Steve
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