Re: [PATCH v5 5/5] arm64: ipi_nmi: Add support for NMI backtrace

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 <redacted>
---
 arch/arm64/include/asm/irq.h |  6 ++++++
 arch/arm64/kernel/ipi_nmi.c  | 12 +++++++++++-
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/irq.h b/arch/arm64/include/asm/irq.h
index b2b0c64..e840bf1 100644
--- a/arch/arm64/include/asm/irq.h
+++ b/arch/arm64/include/asm/irq.h

@@ -6,6 +6,12 @@
 
 #include <asm-generic/irq.h>
 
+#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
+
 struct pt_regs;
 
 static inline int nr_legacy_irqs(void)

diff --git a/arch/arm64/kernel/ipi_nmi.c b/arch/arm64/kernel/ipi_nmi.c
index e0a9e03..e1dc19d 100644
--- a/arch/arm64/kernel/ipi_nmi.c
+++ b/arch/arm64/kernel/ipi_nmi.c

@@ -9,6 +9,7 @@
 #include <linux/interrupt.h>
 #include <linux/irq.h>
 #include <linux/kgdb.h>
+#include <linux/nmi.h>
 #include <linux/smp.h>
 
 #include <asm/nmi.h>

@@ -25,12 +26,21 @@ void arch_send_call_nmi_func_ipi_mask(cpumask_t *mask)
 	__ipi_send_mask(ipi_desc, mask);
 }
 
+void arch_trigger_cpumask_backtrace(const cpumask_t *mask, bool exclude_self)
+{
+	nmi_trigger_cpumask_backtrace(mask, exclude_self,
+				      arch_send_call_nmi_func_ipi_mask);
+}
+
 static irqreturn_t ipi_nmi_handler(int irq, void *data)
 {
 	unsigned int cpu = smp_processor_id();
 
-	ipi_kgdb_nmicallback(cpu, get_irq_regs());
+	if (nmi_cpu_backtrace(get_irq_regs()))
+		goto out;
 
+	ipi_kgdb_nmicallback(cpu, get_irq_regs());
+out:
 	return IRQ_HANDLED;
 }
 

--