linux-kernel - Re: [PATCH 3/3] early_printk: Add simple serialization to early

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Message-ID: <20171004152423.pifhlr72y2uzq63r@hirez.programming.kicks-ass.net>
Date:   Wed, 4 Oct 2017 17:24:23 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>, pmladek@...e.com,
        sergey.senozhatsky@...il.com, linux-kernel@...r.kernel.org,
        mingo@...nel.org, tglx@...utronix.de
Subject: Re: [PATCH 3/3] early_printk: Add simple serialization to
 early_vprintk()

On Wed, Oct 04, 2017 at 07:17:45AM -0700, Paul E. McKenney wrote:
> If you use READ_ONCE(), then all architectures I know of enforce
> full ordering for accesses to a single variable.  (If you don't use
> READ_ONCE(), then in theory Itanium can reorder reads.)  Me, I would
> argue for WRITE_ONCE() as well to prevent store tearing.

Note that the stores are either cmpxchg() or smp_store_release() both of
which imply a WRITE_ONCE().