[PATCH 2/3] arm64: Add support for on-demand backtrace of other CPUs

[Wei Li]

To support backtracing of other CPUs in the system on lockups, add the
implementation of arch_trigger_cpumask_backtrace() for arm64.

In this patch, we add an arm64 NMI-like IPI based backtracer, referring
to the implementation on arm by Russell King and Chris Metcalf.

Signed-off-by: Wei Li <liwei391@xxxxxxxxxx>
---
 arch/arm64/include/asm/hardirq.h |  2 +-
 arch/arm64/include/asm/irq.h     |  6 ++++++
 arch/arm64/kernel/smp.c          | 22 +++++++++++++++++++++-
 3 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/hardirq.h b/arch/arm64/include/asm/hardirq.h
index 89691c86640a..a5d94aa59c7c 100644
--- a/arch/arm64/include/asm/hardirq.h
+++ b/arch/arm64/include/asm/hardirq.h
@@ -24,7 +24,7 @@
 #include <asm/kvm_arm.h>
 #include <asm/sysreg.h>
 
-#define NR_IPI	7
+#define NR_IPI	8
 
 typedef struct {
 	unsigned int __softirq_pending;
diff --git a/arch/arm64/include/asm/irq.h b/arch/arm64/include/asm/irq.h
index b2b0c6405eb0..28471df488c0 100644
--- a/arch/arm64/include/asm/irq.h
+++ b/arch/arm64/include/asm/irq.h
@@ -13,5 +13,11 @@ static inline int nr_legacy_irqs(void)
 	return 0;
 }
 
+#ifdef CONFIG_SMP
+extern void arch_trigger_cpumask_backtrace(const cpumask_t *mask,
+					   bool exclude_self);
+#define arch_trigger_cpumask_backtrace arch_trigger_cpumask_backtrace
+#endif
+
 #endif /* !__ASSEMBLER__ */
 #endif
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index bd8fdf6fcd8e..7e862f9124f3 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -35,6 +35,7 @@
 #include <linux/smp.h>
 #include <linux/seq_file.h>
 #include <linux/irq.h>
+#include <linux/nmi.h>
 #include <linux/irqchip/arm-gic-v3.h>
 #include <linux/percpu.h>
 #include <linux/clockchips.h>
@@ -83,7 +84,8 @@ enum ipi_msg_type {
 	IPI_CPU_CRASH_STOP,
 	IPI_TIMER,
 	IPI_IRQ_WORK,
-	IPI_WAKEUP
+	IPI_WAKEUP,
+	IPI_CPU_BACKTRACE
 };
 
 #ifdef CONFIG_HOTPLUG_CPU
@@ -787,6 +789,7 @@ static const char *ipi_types[NR_IPI] __tracepoint_string = {
 	S(IPI_TIMER, "Timer broadcast interrupts"),
 	S(IPI_IRQ_WORK, "IRQ work interrupts"),
 	S(IPI_WAKEUP, "CPU wake-up interrupts"),
+	S(IPI_CPU_BACKTRACE, "Backtrace interrupts"),
 };
 
 static void smp_cross_call(const struct cpumask *target, unsigned int ipinr)
@@ -946,6 +949,12 @@ void handle_IPI(int ipinr, struct pt_regs *regs)
 		break;
 #endif
 
+	case IPI_CPU_BACKTRACE:
+		nmi_enter();
+		nmi_cpu_backtrace(regs);
+		nmi_exit();
+		break;
+
 	default:
 		pr_crit("CPU%u: Unknown IPI message 0x%x\n", cpu, ipinr);
 		break;
@@ -1070,4 +1079,15 @@ bool cpus_are_stuck_in_kernel(void)
 
 void ipi_gic_nmi_setup(void __iomem *base)
 {
+	gic_sgi_set_prio(base, IPI_CPU_BACKTRACE, GICD_INT_NMI_PRI);
+}
+
+static void raise_nmi(cpumask_t *mask)
+{
+	smp_cross_call(mask, IPI_CPU_BACKTRACE);
+}
+
+void arch_trigger_cpumask_backtrace(const cpumask_t *mask, bool exclude_self)
+{
+	nmi_trigger_cpumask_backtrace(mask, exclude_self, raise_nmi);
 }
-- 
2.17.1