powerpc: Add irq accounting for watchdog interrupts

This adds an irq counter for the watchdog soft-NMI. This interrupt
only fires when interrupts are soft-disabled, so it will not
increment much even when the watchdog is running. However it's
useful for debugging and sanity checking.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/hardirq.h

@@ -13,6 +13,9 @@ typedef struct {
 	unsigned int spurious_irqs;
 	unsigned int hmi_exceptions;
 	unsigned int sreset_irqs;
+#ifdef CONFIG_PPC_WATCHDOG
+	unsigned int soft_nmi_irqs;
+#endif
 #ifdef CONFIG_PPC_DOORBELL
 	unsigned int doorbell_irqs;
 #endif

arch/powerpc/kernel/irq.c

@@ -475,6 +475,13 @@ int arch_show_interrupts(struct seq_file *p, int prec)
 		seq_printf(p, "%10u ", per_cpu(irq_stat, j).sreset_irqs);
 	seq_printf(p, "  System Reset interrupts\n");
 
+#ifdef CONFIG_PPC_WATCHDOG
+	seq_printf(p, "%*s: ", prec, "WDG");
+	for_each_online_cpu(j)
+		seq_printf(p, "%10u ", per_cpu(irq_stat, j).soft_nmi_irqs);
+	seq_printf(p, "  Watchdog soft-NMI interrupts\n");
+#endif
+
 #ifdef CONFIG_PPC_DOORBELL
 	if (cpu_has_feature(CPU_FTR_DBELL)) {
 		seq_printf(p, "%*s: ", prec, "DBL");
@@ -500,6 +507,9 @@ u64 arch_irq_stat_cpu(unsigned int cpu)
 	sum += per_cpu(irq_stat, cpu).timer_irqs_others;
 	sum += per_cpu(irq_stat, cpu).hmi_exceptions;
 	sum += per_cpu(irq_stat, cpu).sreset_irqs;
+#ifdef CONFIG_PPC_WATCHDOG
+	sum += per_cpu(irq_stat, cpu).soft_nmi_irqs;
+#endif
 #ifdef CONFIG_PPC_DOORBELL
 	sum += per_cpu(irq_stat, cpu).doorbell_irqs;
 #endif

arch/powerpc/kernel/watchdog.c

@@ -204,6 +204,9 @@ void soft_nmi_interrupt(struct pt_regs *regs)
 		return;
 
 	nmi_enter();
+
+	__this_cpu_inc(irq_stat.soft_nmi_irqs);
+
 	tb = get_tb();
 	if (tb - per_cpu(wd_timer_tb, cpu) >= wd_panic_timeout_tb) {
 		per_cpu(wd_timer_tb, cpu) = tb;