linux-kernel - [PATCH v7 5/7] arm64: ipi_nmi: Add support for NMI backtrace

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Date:   Mon,  2 Nov 2020 17:14:45 +0530
From:   Sumit Garg <sumit.garg@...aro.org>
To:     maz@...nel.org, catalin.marinas@....com, will@...nel.org,
        daniel.thompson@...aro.org
Cc:     linux-arm-kernel@...ts.infradead.org, tglx@...utronix.de,
        jason@...edaemon.net, linux@...linux.org.uk,
        tsbogend@...ha.franken.de, mpe@...erman.id.au, davem@...emloft.net,
        mingo@...hat.com, bp@...en8.de, x86@...nel.org,
        mark.rutland@....com, julien.thierry.kdev@...il.com,
        dianders@...omium.org, jason.wessel@...driver.com,
        msys.mizuma@...il.com, ito-yuichi@...itsu.com,
        kgdb-bugreport@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
        Sumit Garg <sumit.garg@...aro.org>
Subject: [PATCH v7 5/7] 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 <sumit.garg@...aro.org>
---
 arch/arm64/include/asm/irq.h |  6 ++++++
 arch/arm64/kernel/ipi_nmi.c  | 18 ++++++++++++++++--
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/irq.h b/arch/arm64/include/asm/irq.h
index b2b0c64..ef018a8 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 bool 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 a945dcf..597dcf7 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(int cpu)
-- 
2.7.4