linux-kernel - [PATCH 2/3] x86/mce: Remove explicit smp

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Date:	Wed,  6 Apr 2016 10:05:15 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	X86 ML <x86@...nel.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
	linux-edac <linux-edac@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tony Luck <tony.luck@...el.com>
Subject: [PATCH 2/3] x86/mce: Remove explicit smp_rmb() when starting CPUs sync

From: Davidlohr Bueso <dave@...olabs.net>

mce_start() has an explicit smp_wmb() to serialize writes to global_nwo
and mce_callin. However, atomic_inc_return() implies barriers on both
sides of the call, as such simply rely on this full SMP barrier.

Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: linux-edac <linux-edac@...r.kernel.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Tony Luck <tony.luck@...el.com>
Cc: x86-ml <x86@...nel.org>
Link: http://lkml.kernel.org/r/1458602396-840-1-git-send-email-dave@stgolabs.net
Signed-off-by: Borislav Petkov <bp@...e.de>
---
 arch/x86/kernel/cpu/mcheck/mce.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index f0c921b03e42..6b7039c166b8 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -830,9 +830,9 @@ static int mce_start(int *no_way_out)
 
 	atomic_add(*no_way_out, &global_nwo);
 	/*
-	 * global_nwo should be updated before mce_callin
+	 * Rely on the implied barrier below, such that global_nwo
+	 * is updated before mce_callin.
 	 */
-	smp_wmb();
 	order = atomic_inc_return(&mce_callin);
 
 	/*
-- 
2.7.3