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From:   Sumit Garg <sumit.garg@linaro.org>
To:     maz@kernel.org, catalin.marinas@arm.com, will@kernel.org
Cc:     linux-arm-kernel@lists.infradead.org, tglx@linutronix.de,
        jason@lakedaemon.net, mark.rutland@arm.com,
        julien.thierry.kdev@gmail.com, dianders@chromium.org,
        daniel.thompson@linaro.org, jason.wessel@windriver.com,
        msys.mizuma@gmail.com, ito-yuichi@fujitsu.com,
        kgdb-bugreport@lists.sourceforge.net, linux-kernel@vger.kernel.org,
        Sumit Garg <sumit.garg@linaro.org>
Subject: [PATCH v5 5/5] arm64: ipi_nmi: Add support for NMI backtrace
Date:   Wed, 14 Oct 2020 16:42:11 +0530
Message-Id: <1602673931-28782-6-git-send-email-sumit.garg@linaro.org>
In-Reply-To: <1602673931-28782-1-git-send-email-sumit.garg@linaro.org>
References: <1602673931-28782-1-git-send-email-sumit.garg@linaro.org>
Precedence: bulk

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@linaro.org>
---
 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;
 }
 
-- 
2.7.4