2020-11-02 11:50:10

by Sumit Garg

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 <[email protected]>
---
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

2020-11-02 16:22:59

by Masayoshi Mizuma

Subject: Re: [PATCH v7 5/7] arm64: ipi_nmi: Add support for NMI backtrace

On Mon, Nov 02, 2020 at 05:14:45PM +0530, Sumit Garg wrote:
> 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 <[email protected]>
> ---
> 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)
> --

It works well with sysrq l trigger.
Please feel free to add:

Tested-by: Masayoshi Mizuma <[email protected]>

Thanks!
Masa