[PATCH] i386 nmi_watchdog: Merge check_nmi_watchdog fixes from x86_64

The per cpu nmi watchdog timer is based on an event counter.  idle cpus
don't generate events so the NMI watchdog doesn't fire and the test to see
if the watchdog is working fails.

- Add nmi_cpu_busy so idle cpus don't mess up the test.
- kmalloc prev_nmi_count to keep kernel stack usage bounded.
- Improve the error message on failure so there is enough
  information to debug problems.
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/i386/kernel/nmi.c

@@ -100,16 +100,44 @@ int nmi_active;
 	(P4_CCCR_OVF_PMI0|P4_CCCR_THRESHOLD(15)|P4_CCCR_COMPLEMENT|	\
 	 P4_CCCR_COMPARE|P4_CCCR_REQUIRED|P4_CCCR_ESCR_SELECT(4)|P4_CCCR_ENABLE)
 
+#ifdef CONFIG_SMP
+/* The performance counters used by NMI_LOCAL_APIC don't trigger when
+ * the CPU is idle. To make sure the NMI watchdog really ticks on all
+ * CPUs during the test make them busy.
+ */
+static __init void nmi_cpu_busy(void *data)
+{
+	volatile int *endflag = data;
+	local_irq_enable();
+	/* Intentionally don't use cpu_relax here. This is
+	   to make sure that the performance counter really ticks,
+	   even if there is a simulator or similar that catches the
+	   pause instruction. On a real HT machine this is fine because
+	   all other CPUs are busy with "useless" delay loops and don't
+	   care if they get somewhat less cycles. */
+	while (*endflag == 0)
+		barrier();
+}
+#endif
+
 static int __init check_nmi_watchdog(void)
 {
-	unsigned int prev_nmi_count[NR_CPUS];
+	volatile int endflag = 0;
+	unsigned int *prev_nmi_count;
 	int cpu;
 
 	if (nmi_watchdog == NMI_NONE)
 		return 0;
 
+	prev_nmi_count = kmalloc(NR_CPUS * sizeof(int), GFP_KERNEL);
+	if (!prev_nmi_count)
+		return -1;
+
 	printk(KERN_INFO "Testing NMI watchdog ... ");
 
+	if (nmi_watchdog == NMI_LOCAL_APIC)
+		smp_call_function(nmi_cpu_busy, (void *)&endflag, 0, 0);
+
 	for (cpu = 0; cpu < NR_CPUS; cpu++)
 		prev_nmi_count[cpu] = per_cpu(irq_stat, cpu).__nmi_count;
 	local_irq_enable();
@@ -123,12 +151,18 @@ static int __init check_nmi_watchdog(void)
 			continue;
 #endif
 		if (nmi_count(cpu) - prev_nmi_count[cpu] <= 5) {
-			printk("CPU#%d: NMI appears to be stuck!\n", cpu);
+			endflag = 1;
+			printk("CPU#%d: NMI appears to be stuck (%d->%d)!\n",
+				cpu,
+				prev_nmi_count[cpu],
+				nmi_count(cpu));
 			nmi_active = 0;
 			lapic_nmi_owner &= ~LAPIC_NMI_WATCHDOG;
+			kfree(prev_nmi_count);
 			return -1;
 		}
 	}
+	endflag = 1;
 	printk("OK.\n");
 
 	/* now that we know it works we can reduce NMI frequency to
@@ -136,6 +170,7 @@ static int __init check_nmi_watchdog(void)
 	if (nmi_watchdog == NMI_LOCAL_APIC)
 		nmi_hz = 1;
 
+	kfree(prev_nmi_count);
 	return 0;
 }
 /* This needs to happen later in boot so counters are working */