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 <[email protected]>
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
-
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