linux-kernel - Re: [PATCH v6 5/6] MCS Lock: Restructure the MCS lock defines and locking code into its own file

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Message-ID: <20130927141845.GB15690@laptop.programming.kicks-ass.net>
Date:	Fri, 27 Sep 2013 16:18:45 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Joe Perches <joe@...ches.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Jason Low <jason.low2@...com>,
	Davidlohr Bueso <davidlohr@...com>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Alex Shi <alex.shi@...aro.org>,
	Andi Kleen <andi@...stfloor.org>,
	Michel Lespinasse <walken@...gle.com>,
	Davidlohr Bueso <davidlohr.bueso@...com>,
	Matthew R Wilcox <matthew.r.wilcox@...el.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Rik van Riel <riel@...hat.com>,
	Peter Hurley <peter@...leysoftware.com>,
	linux-kernel@...r.kernel.org, linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH v6 5/6] MCS Lock: Restructure the MCS lock defines and
 locking code into its own file

On Fri, Sep 27, 2013 at 07:05:00AM -0700, Joe Perches wrote:
> On Fri, 2013-09-27 at 15:48 +0200, Peter Zijlstra wrote:
> > On Fri, Sep 27, 2013 at 06:44:55AM -0700, Joe Perches wrote:
> > > It's a CHK test, so it's only tested with --strict
> > > 
> > > $ scripts/checkpatch.pl -f --strict kernel/mutex.c 2>&1 | grep memory
> > > CHECK: memory barrier without comment
> > > CHECK: memory barrier without comment
> > > 
> > > It could be changed to WARN so it's always on.
> > 
> > Yes please, we can't be too careful with memory barriers.
> 
> I'll send the patch separately.
> 
> It seems a pretty noisy test.
> There are 13 hits just in arch/x86/kernel/

Urgh. that wants fixing. We really need to stop getting more and that's
where checkpatch is good at.

At very very bare minimum the comment should mention where the pairing
barrier is; but ideally it should describe the actual ordering.
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