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

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Message-ID: <20170731150411.wff4c5qyanv7xtfy@hirez.programming.kicks-ass.net>
Date:   Mon, 31 Jul 2017 17:04:11 +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 10:23:23AM -0400, Steven Rostedt wrote:
> > -	smp_wmb();
> 
> Heh, I think this was a "lets not leak bp_patching_in_progress" out of
> this function. But I don't see any harm if it happens.
> 
> As this function was a *very* slow path, that smp_wmb() was a "it's not
> really needed, but it wont hurt anything to slap it in there just in
> case".

Well, this is x86, its a NO-OP. The only reason to write barriers like
that is for documentation purposes and in that regard is confuses. IOW
has negative value.