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

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Message-ID: <1415936460.5912.1.camel@perches.com>
Date:	Thu, 13 Nov 2014 19:41:00 -0800
From:	Joe Perches <joe@...ches.com>
To:	Pranith Kumar <bobby.prani@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Petr Mladek <pmladek@...e.cz>, Jan Kara <jack@...e.cz>,
	"Luis R. Rodriguez" <mcgrof@...e.com>,
	Alex Elder <elder@...aro.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	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 Thu, 2014-11-13 at 22:21 -0500, Pranith Kumar wrote:
> Remove volatile type qualifier and use ACCESS_ONCE() in its place for each
> access. Using volatile is not recommended as documented in
> Documentation/volatile-considered-harmful.txt.
> 
> Here logbuf_cpu is a local variable and it is not clear how it is being accessed
> concurrently. We should remove volatile accesses entirely here, but for now make
> a safer change of using ACCESS_ONCE().

Not recommended does not mean "don't ever use".

Forcing the volatile at each use site instead
of the declaration isn't necessarily better.

I think the code is more readable as-is but I'm
not going to object if Andrew picks this up...


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