linux-kernel - Re: [RFC][PATCH]: x86: clarify/fix no-op barriers for text_poke

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Date:   Mon, 31 Jul 2017 17:26:17 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     jkosina@...e.cz, masami.hiramatsu.pt@...achi.com,
        hpa@...ux.intel.com, linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [RFC][PATCH]: x86: clarify/fix no-op barriers for text_poke_bp()

On Mon, Jul 31, 2017 at 11:16:48AM -0400, Steven Rostedt wrote:
> On Mon, 31 Jul 2017 17:04:11 +0200
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > Well, this is x86, its a NO-OP. The only reason to write barriers like
> 
> Is it really a nop?

smp_wmb() is ever since we killed OOSTORE, and smp_rmb() is effectively
(I don't think anybody uses PPRO_FENCE).

The normal x86 TSO memory model doesn't need read or write barriers --
only weird and wonderful (broken) x86 bits do.