[PATCH v8 05/10] arm64: ipi_nmi: Add support for NMI backtrace

[Douglas Anderson]

From: Sumit Garg <sumit.garg at linaro.org>

Enable NMI backtrace support on arm64 using IPI turned as an NMI
leveraging pseudo NMIs support. It is now possible for users to get a
backtrace of a CPU stuck in hard-lockup using magic SYSRQ.

Signed-off-by: Sumit Garg <sumit.garg at linaro.org>
Tested-by: Masayoshi Mizuma <m.mizuma at jp.fujitsu.com>
Tested-by: Chen-Yu Tsai <wens at csie.org>
Signed-off-by: Douglas Anderson <dianders at chromium.org>
---

Changes in v8:
- Removed "#ifdef CONFIG_SMP" since arm64 is always SMP

 arch/arm64/include/asm/irq.h |  4 ++++
 arch/arm64/kernel/ipi_nmi.c  | 18 ++++++++++++++++--
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/irq.h b/arch/arm64/include/asm/irq.h
index fac08e18bcd5..dc35b9d23a81 100644
--- a/arch/arm64/include/asm/irq.h
+++ b/arch/arm64/include/asm/irq.h
@@ -6,6 +6,10 @@
 
 #include <asm-generic/irq.h>
 
+extern bool arch_trigger_cpumask_backtrace(const cpumask_t *mask,
+					   bool exclude_self);
+#define arch_trigger_cpumask_backtrace arch_trigger_cpumask_backtrace
+
 struct pt_regs;
 
 int set_handle_irq(void (*handle_irq)(struct pt_regs *));
diff --git a/arch/arm64/kernel/ipi_nmi.c b/arch/arm64/kernel/ipi_nmi.c
index 712411eed949..c592e92b8cbf 100644
--- a/arch/arm64/kernel/ipi_nmi.c
+++ b/arch/arm64/kernel/ipi_nmi.c
@@ -8,6 +8,7 @@
 
 #include <linux/interrupt.h>
 #include <linux/irq.h>
+#include <linux/nmi.h>
 #include <linux/smp.h>
 
 #include <asm/nmi.h>
@@ -31,11 +32,24 @@ void arm64_send_nmi(cpumask_t *mask)
 	__ipi_send_mask(ipi_nmi_desc, mask);
 }
 
+bool arch_trigger_cpumask_backtrace(const cpumask_t *mask, bool exclude_self)
+{
+	if (!ipi_nmi_desc)
+		return false;
+
+	nmi_trigger_cpumask_backtrace(mask, exclude_self, arm64_send_nmi);
+
+	return true;
+}
+
 static irqreturn_t ipi_nmi_handler(int irq, void *data)
 {
-	/* nop, NMI handlers for special features can be added here. */
+	irqreturn_t ret = IRQ_NONE;
+
+	if (nmi_cpu_backtrace(get_irq_regs()))
+		ret = IRQ_HANDLED;
 
-	return IRQ_NONE;
+	return ret;
 }
 
 void dynamic_ipi_setup(void)
-- 
2.40.0.634.g4ca3ef3211-goog