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: <1380290700.17366.95.camel@joe-AO722>
Date:	Fri, 27 Sep 2013 07:05:00 -0700
From:	Joe Perches <joe@...ches.com>
To:	Peter Zijlstra <peterz@...radead.org>
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, 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/

$ ./scripts/checkpatch.pl -f arch/x86/kernel/*.c | grep -A3 "memory barrier"
WARNING: memory barrier without comment
#685: FILE: x86/kernel/alternative.c:685:
+	smp_wmb();

--
WARNING: memory barrier without comment
#401: FILE: x86/kernel/kvm.c:401:
+		rmb();

WARNING: memory barrier without comment
#403: FILE: x86/kernel/kvm.c:403:
+		rmb();

--
WARNING: memory barrier without comment
#702: FILE: x86/kernel/kvm.c:702:
+	smp_wmb();

WARNING: memory barrier without comment
#704: FILE: x86/kernel/kvm.c:704:
+	smp_wmb();

--
WARNING: memory barrier without comment
#62: FILE: x86/kernel/ldt.c:62:
+	wmb();

WARNING: memory barrier without comment
#64: FILE: x86/kernel/ldt.c:64:
+	wmb();

--
WARNING: memory barrier without comment
#204: FILE: x86/kernel/smpboot.c:204:
+	wmb();

WARNING: memory barrier without comment
#265: FILE: x86/kernel/smpboot.c:265:
+	wmb();

--
WARNING: memory barrier without comment
#557: FILE: x86/kernel/smpboot.c:557:
+	mb();

--
WARNING: memory barrier without comment
#1065: FILE: x86/kernel/smpboot.c:1065:
+	mb();

--
WARNING: memory barrier without comment
#1321: FILE: x86/kernel/smpboot.c:1321:
+	mb();

WARNING: memory barrier without comment
#1399: FILE: x86/kernel/smpboot.c:1399:
+		mb();



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