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Subject: [PATCH] remove volatile from nmi.c
From: Steven Rostedt <rostedt@goodmis.org>
To: Andrew Morton <akpm@osdl.org>
Cc: Ingo Molnar <mingo@elte.hu>, Linus Torvalds <torvalds@osdl.org>,
       LKML <linux-kernel@vger.kernel.org>
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Date: Fri, 14 Jul 2006 09:04:48 -0400
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OK, I'm using this as something of an exercise to completely understand
memory barriers.  So if something is incorrect, please let me know.

This patch removes the volatile keyword from arch/i386/kernel/nmi.c.

The first removal is trivial, since the barrier in the while loop makes
it unnecessary. (as proved in "[patch] spinlocks: remove 'volatile'"
thread)
http://marc.theaimsgroup.com/?l=linux-kernel&m=115217423929806&w=2


The second is what I think is correct.  So please review.

Thanks,

-- Steve

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

Index: linux-2.6.18-rc1/arch/i386/kernel/nmi.c
===================================================================
--- linux-2.6.18-rc1.orig/arch/i386/kernel/nmi.c	2006-07-14 08:35:00.000000000 -0400
+++ linux-2.6.18-rc1/arch/i386/kernel/nmi.c	2006-07-14 08:38:07.000000000 -0400
@@ -106,7 +106,7 @@ int nmi_active;
  */
 static __init void nmi_cpu_busy(void *data)
 {
-	volatile int *endflag = data;
+	int *endflag = data;
 	local_irq_enable_in_hardirq();
 	/* Intentionally don't use cpu_relax here. This is
 	   to make sure that the performance counter really ticks,
@@ -121,7 +121,7 @@ static __init void nmi_cpu_busy(void *da
 
 static int __init check_nmi_watchdog(void)
 {
-	volatile int endflag = 0;
+	int endflag = 0;
 	unsigned int *prev_nmi_count;
 	int cpu;
 
@@ -150,7 +150,7 @@ static int __init check_nmi_watchdog(voi
 			continue;
 #endif
 		if (nmi_count(cpu) - prev_nmi_count[cpu] <= 5) {
-			endflag = 1;
+			set_wmb(endflag, 1);
 			printk("CPU#%d: NMI appears to be stuck (%d->%d)!\n",
 				cpu,
 				prev_nmi_count[cpu],
@@ -161,7 +161,7 @@ static int __init check_nmi_watchdog(voi
 			return -1;
 		}
 	}
-	endflag = 1;
+	set_wmb(endflag, 1);
 	printk("OK.\n");
 
 	/* now that we know it works we can reduce NMI frequency to